Publications

  • The Future of Attosecond Science

    Dudovich N., Fang L., Gaarde M., Keller U., Landsman A., Richter M., Rohringer N. & Young L. (2024) .
    Conferences are incredible opportunities to strengthen the inclusive outlook of our scientific community. The participation of female scientists, postdocs, and graduate students in the ATTO VIII conference was remarkable, with more than 40% of female invited speakers. The Local Organizing Committee seized this opportunity to promote an atmosphere that welcomes all. An entirely female evening panel, with experience across the attosecond science spectrum, was convened to explore the Future of Attosecond Science in the evening session of Wednesday, July 13. Furthermore, a booklet entitled Perspectives in Attosecond Science was compiled by Dr. Shima Gholam-Mirzaei of the University of Ottawa and ATTO co-chairs Luca Argenti and Michael Chini, in collaboration with members of the Local Organizing Committee and others, which included interviews with female scientists at all career levels and which was included in the conference materials. The text has been minimally edited to improve clarity and readability.

  • Quantum Entangled States of a Classically Radiating Macroscopic Spin

    Somech O. & Shahmoon E. (2024) PRX Quantum.
    Entanglement constitutes a main feature that distinguishes quantum from classical physics and is a key resource of quantum technologies. Here we show, however, that entanglement may also serve as the essential ingredient for the emergence of classical behavior in a composite nonlinear radiating system. We consider the radiation from a macroscopic spin emitter, such as the collective radiation from an atomic ensemble. We introduce a new class of macroscopic spin states, the coherently radiating spin states (CRSS), defined as the asymptotic eigenstates of the SU(2) lowering operator. We find that a spin emitter in a CRSS radiates classical-like coherent light, although the CRSS itself is a quantum entangled state exhibiting spin squeezing. We further show that CRSS are naturally produced in Dicke superradiance and underlie the dissipative Dicke phase transition. Our CRSS theory thus provides new concepts for studying the quantum physics of radiation, with applications in current platforms involving collections of atoms or spins, their consideration in quantum technologies such as metrology and lasing, and the many-body theory of spin systems.

  • Black-hole powered quantum coherent amplifier

    Misra A., Chattopadhyay P., Svidzinsky A., Scully M. O. & Kurizki G. (2024) npj Quantum Information.
    Atoms falling into a black hole (BH) through a cavity are shown to enable coherent amplification of light quanta powered by the BH-gravitational vacuum energy. This process can harness the BH energy towards useful purposes, such as propelling a spaceship trapped by the BH. The process can occur via transient amplification of a signal field by falling atoms that are partly excited by Hawking radiation reflected by an orbiting mirror. In the steady-state regime of thermally equilibrated atoms that weakly couple to the field, this amplifier constitutes a BH-powered quantum heat engine. The envisaged effects substantiate the thermodynamic approach to BH acceleration radiation.

  • Prospects of nuclear-coupled-dark-matter detection via correlation spectroscopy of I<sup>+</sup><sub>2 </sub>and Ca<sup>+</sup>

    Madge E., Perez G. & Meir Z. (2024) arXiv.org.
    The nature of dark matter (DM) and its interaction with the Standard Model (SM) is one of the biggest open questions in physics nowadays. The vast majority of theoretically-motivated Ultralight-DM (ULDM) models predict that ULDM couples dominantly to the SM strong/nuclear sector. This coupling leads to oscillations of nuclear parameters that are detectable by comparing clocks with different sensitivities to these nature's constants. Vibrational transitions of molecular clocks are more sensitive to a change in the nuclear parameters than the electronic transitions of atomic clocks. Here, we propose the iodine molecular ion, I<sup>+</sup><sub>2 </sub>, as a sensitive detector for such a class of ULDM models. The iodine's dense spectrum allows us to match its transition frequency to that of an optical atomic clock (Ca<sup>+</sup>) and perform correlation spectroscopy between the two clock species. With this technique, we project a few-orders-of-magnitude improvement over the most sensitive clock comparisons performed to date. We also briefly consider the robustness of the corresponding "Earth-bound" under modifications of the Z<sub>N</sub>-QCD axion model.

  • Coherent interface between optical and microwave photons on an integrated superconducting atom chip

    Petrosyan D., Fortágh J. & Kurizki G. (2024) EPJ Quantum Technology.
    Sub-wavelength arrays of atoms exhibit remarkable optical properties, analogous to those of phased array antennas, such as collimated directional emission or nearly perfect reflection of light near the collective resonance frequency. We propose to use a single-sheet sub-wavelength array of atoms as a switchable mirror to achieve a coherent interface between propagating optical photons and microwave photons in a superconducting coplanar waveguide resonator. In the proposed setup, the atomic array is located near the surface of the integrated superconducting chip containing the microwave cavity and optical waveguide. A driving laser couples the excited atomic state to Rydberg states with strong microwave transition. Then the presence or absence of a microwave photon in the superconducting cavity makes the atomic array transparent or reflective to the incoming optical pulses of proper frequency and finite bandwidth.

  • Strongly Interacting Bose-Fermi Mixtures: Mediated Interaction, Phase Diagram, and Sound Propagation

    Shen X., Davidson N., Bruun G. M., Sun M. & Wu Z. (2024) Physical review letters.
    Motivated by recent surprising experimental findings, we develop a strong-coupling theory for Bose-Fermi mixtures capable of treating resonant interspecies interactions while satisfying the compressibility sum rule. We show that the mixture can be stable at large interaction strengths close to resonance, in agreement with the experiment, but at odds with the widely used perturbation theory. We also calculate the sound velocity of the Bose gas in the Cs133-Li6 mixture, again finding good agreement with the experimental observations both at weak and strong interactions. A central ingredient of our theory is the generalization of a fermion mediated interaction to strong Bose-Fermi scatterings and to finite frequencies. This further leads to a predicted hybridization of the sound modes of the Bose and Fermi gases, which can be directly observed using Bragg spectroscopy.

  • Real-time adaptive estimation of decoherence timescales for a single qubit

    Arshad M. J., Bekker C., Haylock B., Skrzypczak K., White D., Griffiths B., Gore J., Morley G. W., Salter P., Smith J., Zohar I., Finkler A., Altmann Y., Gauger E. M. & Bonato C. (2024) Physical Review Applied.
    Characterizing the time over which quantum coherence survives is critical for any implementation of quantum bits, memories, and sensors. The usual method for determining a quantum system's decoherence rate involves a suite of experiments probing the entire expected range of this parameter, and extracting the resulting estimation in postprocessing. Here we present an adaptive multiparameter Bayesian approach, based on a simple analytical update rule, to estimate the key decoherence timescales (T1, T2∗ - , and T2) and the corresponding decay exponent of a quantum system in real time, using information gained in preceding experiments. This approach reduces the time required to reach a given uncertainty by a factor up to an order of magnitude, depending on the specific experiment, compared to the standard protocol of curve fitting. A further speedup of a factor approximately 2 can be realized by performing our optimization with respect to sensitivity as opposed to variance.

  • Sensing microscopic noise events by frequent quantum measurements

    Virzì S., Knoll L. T., Avella A., Piacentini F., Gherardini S., Gramegna M., Kurizki G., Kofman A. G., Degiovanni I. P., Genovese M. & Caruso F. (2024) Physical Review Applied.
    We propose and experimentally demonstrate a general method allowing us to unravel microscopic noise events that affect a continuous quantum variable. Such unraveling is achieved by frequent measurements of a discrete variable coupled to the continuous one. The experimental realization involves photons traversing a noisy channel. There, their polarization, whose coupling to the photons' spatial wave packet is subjected to stochastic noise, is frequently measured in the quantum Zeno regime. The measurements not only preserve the polarization state, but also enable the recording of the full noise statistics from the spatially resolved detection of the photons emerging from the channel. This method proves the possibility of employing photons as quantum noise sensors and robust carriers of information.

  • Use of spatiotemporal couplings and an axiparabola to control the velocity of peak intensity

    Liberman A., Lahaye R., Smartsev S., Tata S., Benracassa S., Golovanov A., Levine E., Thaury C. & Malka V. (2024) Optics Letters.
    This paper presents the first experimental realization of a scheme that allows for the tuning of the velocity of peak intensity of a focal spot with relativistic intensity. By combining a tunable pulse-front curvature with the axial intensity deposition characteristics of an axiparabola, an aspheric optical element, this system provides control over the dynamics of laser-wakefield accelerators. We demonstrate the ability to modify the velocity of peak intensity of ultrashort laser pulses to be superluminal or subluminal. The experimental results are supported by theoretical calculations and simulations, strengthening the case for the axiparabola as a pertinent strategy to achieve more efficient acceleration.

  • Laser-Induced Electron Diffraction in Chiral Molecules

    Rajak D., Beauvarlet S., Kneller O., Comby A., Cireasa R., Descamps D., Fabre B., Gorfinkiel J. D., Higuet J., Petit S., Rozen S., Ruf H., Thiré N., Blanchet V., Dudovich N., Pons B. & Mairesse Y. (2024) Physical Review X.
    Strong laser pulses enable probing molecules with their own electrons. The oscillating electric field tears electrons off a molecule, accelerates them, and drives them back toward their parent ion within a few femtoseconds. The electrons are then diffracted by the molecular potential, encoding its structure and dynamics with angstrom and attosecond resolutions. Using elliptically polarized laser pulses, we show that laser-induced electron diffraction is sensitive to the chirality of the target. The field selectively ionizes molecules of a given orientation and drives the electrons along different sets of trajectories, leading them to recollide from different directions. Depending on the handedness of the molecule, the electrons are preferentially diffracted forward or backward along the light propagation axis. This asymmetry, reaching several percent, can be reversed for electrons recolliding from two ends of the molecule. The chiral sensitivity of laser-induced electron diffraction opens a new path to resolve ultrafast chiral dynamics.

  • Real-time visualization of the laser-plasma wakefield dynamics

    Wan Y., Tata S., Seemann O., Levine E. Y., Kroupp E. & Malka V. (2024) Science advances.
    The exploration of new acceleration mechanisms for compactly delivering high-energy particle beams has gained great attention in recent years. One alternative that has attracted particular interest is the plasma-based wakefield accelerator, which is capable of sustaining accelerating fields that are more than three orders of magnitude larger than those of conventional radio-frequency accelerators. In this device, acceleration is generated by plasma waves that propagate at nearly light speed, driven by intense lasers or charged particle beams. Here, we report on the direct visualization of the entire plasma wake dynamics by probing it with a femtosecond relativistic electron bunch. This includes the excitation of the laser wakefield, the increase of its amplitude, the electron injection, and the transition to the beam-driven plasma wakefield. These experimental observations provide first-hand valuable insights into the complex physics of laser beam-plasma interaction and demonstrate a powerful tool that can largely advance the development of plasma accelerators for real-time operation.

  • Observation of interband Berry phase in laser-driven crystals

    Uzan-Narovlansky A. J., Faeyrman L., Brown G. G., Shames S., Narovlansky V., Xiao J., Arusi-Parpar T., Kneller O., Bruner B. D., Smirnova O., Silva R. E., Yan B., Jiménez-Galán Á., Ivanov M. & Dudovich N. (2024) Nature.
    Ever since its discovery<sup> 1</sup>, the notion of the Berry phase has permeated all branches of physics and plays an important part in a variety of quantum phenomena<sup> 2</sup>. However, so far all its realizations have been based on a continuous evolution of the quantum state, following a cyclic path. Here we introduce and demonstrate a conceptually new manifestation of the Berry phase in light-driven crystals, in which the electronic wavefunction accumulates a geometric phase during a discrete evolution between different bands, while preserving the coherence of the process. We experimentally reveal this phase by using a strong laser field to engineer an internal interferometer, induced during less than one cycle of the driving field, which maps the phase onto the emission of higher-order harmonics. Our work provides an opportunity for the study of geometric phases, leading to a variety of observations in light-driven topological phenomena and attosecond solid-state physics.

  • Enhanced persistent orientation of asymmetric-top molecules induced by cross-polarized terahertz pulses

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. (2024) Physical Review Research.
    We investigate the persistent orientation of asymmetric-top molecules induced by time-delayed THz pulses that are either collinearly or cross polarized. Our theoretical and numerical results demonstrate that the orthogonal configuration outperforms the collinear one, and a significant degree of persistent orientation - approximately 10% at 5 K and nearly 3% at room temperature - may be achieved through parameter optimization. The dependence of the persistent orientation factor on temperature and field parameters is studied in detail. The proposed application of two orthogonally polarized THz pulses is both practical and efficient. Its applicability under standard laboratory conditions lays a solid foundation for future experimental realization of THz-induced persistent molecular orientation.

  • Guided Search to Self-Healing in Semiconductors

    Py-Renaudie A., Soffer Y., Singh P., Kumar S., Ceratti D. R., Mualem Y., Rosenhek-Goldian I., Oron D., Cohen S. R., Schulz P., Cahen D. & Guillemoles J. F. (2023) Advanced Functional Materials.
    Self-healing (SH) of (opto)electronic material damage can have a huge impact on resource sustainability. The rising interest in halide perovskite (HaP) compounds over the past decade is due to their excellent semiconducting properties for crystals and films, even if made by low-temperature solution-based processing. Direct proof of self-healing in Pb-based HaPs is demonstrated through photoluminescence recovery from photodamage, fracture healing and their use as high-energy radiation and particle detectors. Here, the question of how to find additional semiconducting materials exhibiting SH, in particular lead-free ones is addressed. Applying a data-mining approach to identify semiconductors with favorable mechanical and thermal properties, for which Pb HaPs are clear outliers, it is found that the Cs<sub>2</sub>Au<sup>I</sup>Au<sup>III</sup>X<sub>6</sub>, (X = I, Br, Cl) family, which is synthesized and tested for SH. This is the first demonstration of self-healing of Pb-free inorganic HaP thin films, by photoluminescence recovery.

  • Ultrasensitive Photonic Quantum Noise Sensing by Frequent-measurement Nonlinear Filtering

    Kurizki G., Poem E., Firstenberg O., Opatrný T., Dasari D. B. R., Caruso F., Piacentini F. & Genovese M. (2023) .
    In recent works, we have put forth and experimentally demonstrated several novel schemes [1-5] for the detection of quantum noise signatures by exploiting frequent photonic measurements, allowing us to reach unprecedented, ultrahigh sensitivity to quantum noise.

  • Tailoring quantum trajectories for strong-field imaging

    Sanchez A., Tulsky V. A., Amini K., Bruner B. D., Alon G., Kruger M., Liu X., Steinle T., Bauer D., Dudovich N. & Biegert J. (2023) Optica.
    Strong-field imaging techniques such as laser-induced electron diffraction (LIED) provide unprecedented combined picometer spatial and attosecond temporal resolution by "self-imaging"a molecular target with its own rescattering electrons. Accessing the rich information contained in these experiments requires the ability to accurately manipulate the dynamics of these electrons-namely, their ionization amplitudes, and times of ionization and rescattering-with attosecond to femtosecond precision. The primary challenge is imposed by the multitude of quantum pathways of the photoelectron, reducing the effective measurement to a small range of energies and providing very limited spatial resolution. Here, we show how this ambiguity can be virtually eliminated by manipulating the rescattering pathways with a tailored laser field. Through combined experimental and theoretical approaches, a phase-controlled two-color laser waveformis shown to facilitate the selection of a specific quantum pathway, allowing a direct mapping between the electron's final momentum and the rescattering time. Integrating attosecond control with Ångstrom-scale resolution could advance ultrafast imaging of field-induced quantum phenomena.

  • Beam current from downramp injection in electron-driven plasma wakefields

    Hue C., Golovanov A., Tata S., Corde S. & Malka V. (2023) Journal of Plasma Physics.
    We study the stability of plasma wake wave and the properties of density-downramp injection in an electron-driven plasma accelerator. In this accelerator type, a short high-current electron bunch (generated by a conventional accelerator or a laser-wakefield acceleration stage) drives a strongly nonlinear plasma wake wave (blowout), and accelerated electrons are injected into it using a sharp density transition which leads to the elongation of the wake. The accelerating structure remains highly stable until the moment some electrons of the driver reach almost zero energy, which corresponds to the best interaction length for optimal driver-to-plasma energy transfer efficiency. For a particular driver, this efficiency can be optimised by choosing appropriate plasma density. Studying the dependence of the current of the injected bunch on driver and plasma parameters, we show that it does not depend on the density downramp length as long as the condition for trapping is satisfied. Most importantly, we find that the current of the injected bunch primarily depends on just one parameter which combines both the properties of the driver (its current and duration) and the plasma density.

  • Brilliant whiteness in shrimp from ultra-thin layers of birefringent nanospheres

    Lemcoff T., Alus L., Haataja J. S., Wagner A., Zhang G., Pavan M. J., Yallapragada V. J., Vignolini S., Oron D., Schertel L. & Palmer B. A. (2023) Nature Photonics.
    A fundamental question regarding light scattering is how whiteness, generated from multiple scattering, can be obtained from thin layers of materials. This challenge arises from the phenomenon of optical crowding, whereby, for scatterers packed with filling fractions higher than ~30%, reflectance is drastically reduced due to near-field coupling between the scatterers. Here we show that the extreme birefringence of isoxanthopterin nanospheres overcomes optical crowding effects, enabling multiple scattering and brilliant whiteness from ultra-thin chromatophore cells in shrimp. Strikingly, numerical simulations reveal that birefringence, originating from the spherulitic arrangement of isoxanthopterin molecules, enables intense broadband scattering almost up to the maximal packing for random spheres. This reduces the thickness of material required to produce brilliant whiteness, resulting in a photonic system that is more efficient than other biogenic or biomimetic white materials which operate in the lower refractive index medium of air. These results highlight the importance of birefringence as a structural variable to enhance the performance of such materials and could contribute to the design of biologically inspired replacements for artificial scatterers like titanium dioxide.

  • Colloquium: Anomalous statistics of laser-cooled atoms in dissipative optical lattices

    Afek G., Davidson N., Kessler D. A. & Barkai E. (2023) Reviews of Modern Physics.
    Diffusion occurs in numerous physical systems throughout nature, drawing its generality from the universality of the central limit theorem. Approximately a century ago it was realized that an extension to this type of dynamics can be obtained in the form of "anomalous"diffusion, where distributions are allowed to have heavy power-law tails. Owing to a unique feature of its momentum-dependent dissipative friction force, laser-cooled atomic ensembles can be used as a test bed for such dynamics. The interplay between laser cooling and anomalous dynamics bears deep predictive implications for fundamental concepts in both equilibrium and nonequilibrium statistical physics. The high degree of control available in cold-atom experiments allows for the parameters of the friction to be tuned, revealing transitions in the dynamical properties of the system. Rare events in both the momentum and spatial distributions are described by non-normalized states using tools adapted from infinite ergodic theory. This leads to new experimental and theoretical results that illuminate the various features of the system.

  • How synchronized human networks escape local minima

    Shniderman E., Avraham Y., Shahal S., Duadi H., Davidson N. & Fridman M. (2023) arXiv.org.
    Finding the global minimum in complex networks while avoiding local minima is challenging in many types of networks. We study the dynamics of complex human networks and observed that humans have different methods to avoid local minima than other networks. Humans can change the coupling strength between them or change their tempo. This leads to different dynamics than other networks and makes human networks more robust and better resilient against perturbations. We observed high-order vortex states, oscillation death, and amplitude death, due to the unique dynamics of the network. This research may have implications in politics, economics, pandemic control, decision-making, and predicting the dynamics of networks with artificial intelligence.

  • Fast, noise-free atomic optical memory with 35-percent end-to-end efficiency

    Davidson O., Yogev O., Poem E. & Firstenberg O. (2023) Communications Physics.
    Coherent optical memories will likely play an important role in future quantum communication networks. Among the different platforms, memories based on ladder-type orbital transitions in atomic gasses offer high bandwidth (>100 MHz), continuous (on-demand) readout, and low-noise operation. Here we report on an upgraded setup of our previously-reported fast ladder memory, with improved efficiency and lifetime, and reduced noise. The upgrade employs a stronger control field, wider signal beam, reduced atomic density, higher optical depth, annular optical-pumping beam, and weak dressing of an auxiliary orbital to counteract residual Doppler-broadening. For a 2 ns-long pulse, we demonstrate 53% internal efficiency, 35% end-to-end efficiency, 3 × 10<sup>−5</sup> noise photons per pulse, and a 1/e lifetime of 108 ns. This combination of performances is a record for continuous-readout memories.

  • A new spin on impact ionization

    Kazes M. & Oron D. (2023) Nature Materials.
    Quantum dots are engineered to use dopant states to achieve substantially enhanced impact ionization, which is potentially useful for light-harvesting applications.

  • Room Temperature Relaxometry of Single Nitrogen Vacancy Centers in Proximity to α-RuCl<sub>3</sub> Nanoflakes

    Kumar J., Yudilevich D., Smooha A., Zohar I., Pariari A. K., Stöhr R., Denisenko A., Hücker M. & Finkler A. (2023) Nano Letters.
    Nitrogen vacancy (NV) center-based magnetometry has been proven to be a versatile sensor for various classes of magnetic materials in broad temperature and frequency ranges. Here, we use the longitudinal relaxation time T<sub>1</sub> of single NV centers to investigate the spin dynamics of nanometer-thin flakes of α-RuCl<sub>3</sub> at room temperature. We observe a significant reduction in the T<sub>1</sub> in the presence of α-RuCl<sub>3</sub> in the proximity of NVs, which we attribute to paramagnetic spin noise confined in the 2D hexagonal planes. Furthermore, the T<sub>1</sub> time exhibits a monotonic increase with an applied magnetic field. We associate this trend with the alteration of the spin and charge noise in α-RuCl<sub>3</sub> under an external magnetic field. These findings suggest that the influence of the spin dynamics of α-RuCl<sub>3</sub> on the T<sub>1</sub> of the NV center can be used to gain information about the material itself and the technique to be used on other 2D materials.

  • Excitation Intensity-Dependent Quantum Yield of Semiconductor Nanocrystals

    Ghosh S., Ross U., Chizhik A. M., Kuo Y., Jeong B. G., Bae W. K., Park K., Li J., Oron D., Weiss S., Enderlein J. & Chizhik A. I. (2023) Journal of Physical Chemistry Letters.
    One of the key phenomena that determine the fluorescence of nanocrystals is the nonradiative Auger-Meitner recombination of excitons. This nonradiative rate affects the nanocrystals’ fluorescence intensity, excited state lifetime, and quantum yield. Whereas most of the above properties can be directly measured, the quantum yield is the most difficult to assess. Here we place semiconductor nanocrystals inside a tunable plasmonic nanocavity with subwavelength spacing and modulate their radiative de-excitation rate by changing the cavity size. This allows us to determine absolute values of their fluorescence quantum yield under specific excitation conditions. Moreover, as expected considering the enhanced Auger-Meitner rate for higher multiple excited states, increasing the excitation rate reduces the quantum yield of the nanocrystals.

  • Resolving the Emission Transition Dipole Moments of Single Doubly Excited Seeded Nanorods via Heralded Defocused Imaging

    Amgar D., Lubin G., Yang G., Rabouw F. T. & Oron D. (2023) Nano Letters.
    Semiconductor nanocrystal emission polarization is a crucial probe of nanocrystal physics and an essential factor for nanocrystal-based technologies. While the transition dipole moment for the lowest excited state to ground state transition is well characterized, the dipole moment of higher multiexcitonic transitions is inaccessible via most spectroscopy techniques. Here, we realize direct characterization of the doubly excited-state relaxation transition dipole by heralded defocused imaging. Defocused imaging maps the dipole emission pattern onto a fast single-photon avalanche diode detector array, allowing the postselection of photon pairs emitted from the biexciton-exciton emission cascade and resolving the differences in transition dipole moments. Type-I<sup>1</sup>/<sub>2</sub> seeded nanorods exhibit higher anisotropy of the biexciton-to-exciton transition compared to the exciton-to-ground state transition. In contrast, type-II seeded nanorods display a reduction of biexciton emission anisotropy. These findings are rationalized in terms of an interplay between the transient dynamics of the refractive index and the excitonic fine structure.

  • Selective Detection in Impulsive Low-Frequency Raman Imaging Using Shaped Probe Pulses

    Shivkumar S., Ranann D., Metais S., Suresh S., Forget N., Bartels R., Oron D. & Rigneault H. (2023) Physical Review Applied.
    Impulsive stimulated Raman scattering (ISRS) using a single short femtosecond pump pulse to excite molecular vibrations offers an elegant pump-probe approach to perform vibrational imaging below 200cm<sup>-1</sup>. One shortcoming of ISRS is its inability to offer vibrational selectivity as all the vibrational bonds whose frequencies lie within the short pump-pulse bandwidth are excited. To date, several coherent control techniques have been explored to address this issue and selectively excite a specific molecular vibration by shaping the pump pulse. There has not been any systematic work that reports an analogous shaping of the probe pulse to implement preferential detection. In this work, we focus on vibrational imaging and report vibrational selective detection by shaping the probe pulse in time. We demonstrate numerically and experimentally two pulse-shaping strategies with one functioning as a vibrational notch filter and the other functioning as a vibrational low-pass filter. This enables fast (25μs/pixel) and selective hyperspectral imaging in the low-frequency regime (

  • Roadmap on Label-Free Super-Resolution Imaging

    Astratov V. N., Sahel Y. B., Eldar Y. C., Huang L., Ozcan A., Zheludev N., Zhao J., Burns Z., Liu Z., Narimanov E., Goswami N., Popescu G., Pfitzner E., Kukura P., Hsiao Y. T., Hsieh C. L., Abbey B., Diaspro A., LeGratiet A., Bianchini P., Shaked N. T., Simon B., Verrier N., Debailleul M., Haeberlé O., Wang S., Liu M., Bai Y., Cheng J. X., Kariman B. S., Fujita K., Sinvani M., Zalevsky Z., Li X., Huang G. J., Chu S. W., Tzang O., Hershkovitz D., Cheshnovsky O., Huttunen M. J., Stanciu S. G., Smolyaninova V. N., Smolyaninov I. I., Leonhardt U., Sahebdivan S., Wang Z., Luk'yanchuk B., Wu L., Maslov A. V., Jin B., Simovski C. R., Perrin S., Montgomery P. & Lecler S. (2023) Laser and Photonics Reviews.
    Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles that need to be overcome to break the classical diffraction limit of the label-free imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability that are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.

  • High repetition rate relativistic laser-solid-plasma interaction platform featuring simultaneous particle and radiation detection

    Kaur J., Ouillé M., Levy D., Daniault L., Robbes A., Zaïm N., Flacco A., Kroupp E., Malka V., Haessler S. & Lopez-Martens R. (2023) Review of Scientific Instruments.
    We report on a uniquely designed high repetition rate relativistic laser-solid-plasma interaction platform, featuring the first simultaneous measurement of emitted high-order harmonics, relativistic electrons, and low divergence proton beams. This versatile setup enables detailed parametric studies of the particle and radiation spatio-spectral beam properties under a wide range of controlled interaction conditions, such as pulse duration and plasma density gradient. Its array of complementary diagnostics unlocks the potential to unravel interdependencies among the observables and should aid in further understanding the complex collective dynamics at play during laser-plasma interactions and in optimizing the secondary beam properties for applications.

  • Surface-Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications

    Niazov-Elkan A., Shepelenko M., Alus L., Kazes M., Houben L., Rechav K., Leitus G., Kossoy A., Feldman Y., Kronik L., Vekilov P. G. & Oron D. (2023) Advanced Materials.
    Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300–600 nm thick, are obtained. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals.

  • Universal approach for quantum interfaces with atomic arrays

    Solomons Y., Ben-Maimon R. & Shahmoon E. (2023) arxiv.org.
    We develop a general approach for the characterization of atom-array platforms as light-matter interfaces, focusing on their application in quantum memory and photonic entanglement generation. Our approach is based on the mapping of atom-array problems to a generic 1D model of light interacting with a collective dipole. We find that the efficiency of light-matter coupling, which in turn determines those of quantum memory and entanglement, is given by the on-resonance reflectivity of the 1D scattering problem, r0=C/(1+C), where C is a cooperativity parameter of the model. For 2D and 3D atomic arrays in free space, we derive the mapping parameter C and hence r0, while accounting for realistic effects such as the finite sizes of the array and illuminating beam and weak disorder in atomic positions. Our analytical results are verified numerically and reveal a key idea: efficiencies of quantum tasks are reduced by our approach to the classical calculation of a reflectivity. This provides a unified framework for the analysis of collective light-matter coupling in various relevant platforms such as optical lattices and tweezer arrays. Generalization to collective systems beyond arrays is discussed.

  • Wave correlations and quantum noise in cosmology

    Leonhardt U. (2023) Journal of physics. A, Mathematical and theoretical.
    Wave noise is correlated. While it may look random in space, correlations appear in space–time, because the noise is carried by wave propagation. These correlations of wave noise give rise to fluctuation forces such as the Casimir force, they are responsible for the particle creation in the dynamical Casimir effect and in the expanding Universe. This paper considers the noise correlations for light waves in non-exponentially expanding flat space. The paper determines the high-frequency asymptotics of the correlation spectrum in the conformal vacuum. These noise correlations give rise to a nontrivial vacuum energy that may appear as the cosmological constant.

  • Multichannel waveguide QED with atomic arrays in free space

    Solomons Y. & Shahmoon E. (2023) Physical Review A.
    We study light scattering off a two-dimensional array of atoms driven to Rydberg levels. We show that the problem can be mapped to a generalized model of waveguide QED, consisting of multiple one-dimensional photonic channels (transverse modes), each of which is directionally coupled to a corresponding Rydberg surface mode of the array. In the Rydberg blockade regime, collective excitations of different surface modes block each other, leading to multichannel correlated photonic states. Using an analytical approach, we characterize interchannel quantum correlations, and elucidate the role of collective two-photon resonances of the array. Our results open new possibilities for multimode many-body physics and quantum information with photons in a free-space platform.

  • Excitation transfer in disordered spin chains with long-range exchange interactions

    Palaiodimopoulos N. E., Kiefer-Emmanouilidis M., Kurizki G. & Petrosyan D. (2023) SciPost Physics Core.
    We examine spin excitation or polarization transfer via spin chains with long-range exchange interactions in the presence of diagonal and off-diagonal disorder. To this end, we determine the mean localization length of the single-excitation eigenstates of the chain for various strengths of the disorder. We then identify the energy eigenstates of the system with large localization length and sufficient support at the chain boundaries that are suitable to transfer an excitation between the sender and receiver spins connected to the opposite ends of the chain. We quantify the performance of two transfer schemes involving weak static couplings of the sender and receiver spins to the chain, and time-dependent couplings realizing stimulated adiabatic passage of the excitation via the intermediate eigenstates of the chain which exhibits improved performance.

  • On the absence of the electrostriction force in dilute clouds of cold atoms

    Courvoisier A. & Davidson N. (2023) arXiv.org.
    The momentum of light in a medium and the mechanisms of momentum transfer between light and dielectrics have long been the topic of controversies and confusion. We discuss here the problem of momentum transfers that follow the refraction of light by dilute, inhomogeneous ensembles of ultra-cold atoms. We show experimentally and theoretically that the refraction of light rays by a dilute gas does not entail momentum transfers to first order in the light-atom coupling coefficient, in contradiction with the work reported in Matzliah et al. Phys. Rev. Lett. 119, 189902 (2017).

  • Spin-strain coupling in nanodiamonds as a unique cluster identifier

    Awadallah A., Zohar I. & Finkler A. (2023) Journal of Applied Physics.
    Fluorescent nanodiamonds have been used to a large extent in various biological systems due to their robust nature, their inert properties, and the relative ease of modifying their surface for attachment to different functional groups. Within a given batch, however, each nanodiamond is indistinguishable from its neighbors and, so far, one could only rely on fluorescence statistics for some global information about the ensemble. Here, we propose and measure the possibility of adding another layer of unique information, relying on the coupling between the strain in the nanodiamond and the spin degree-of-freedom in the nitrogen-vacancy center in diamond. We show that the large variance in axial and transverse strain can be encoded to an individual radio frequency identity for a cluster of nanodiamonds. When using single nanodiamonds, this unique fingerprint can then be potentially tracked in real-time in, e.g., cells, as their size is compatible with metabolism intake. From a completely different aspect, in clusters of nanodiamonds, this can already serve as a platform for anti-counterfeiting measures.

  • Advances in device-independent quantum key distribution

    Zapatero V., van Leent T., Arnon-Friedman R., Liu W. Z., Zhang Q., Weinfurter H. & Curty M. (2023) npj Quantum Information.
    Device-independent quantum key distribution (DI-QKD) provides the gold standard for secure key exchange. Not only does it allow for information-theoretic security based on quantum mechanics, but it also relaxes the need to physically model the devices, thereby fundamentally ruling out many quantum hacking threats to which non-DI QKD systems are vulnerable. In practice though, DI-QKD is very challenging. It relies on the loophole-free violation of a Bell inequality, a task that requires high quality entanglement to be distributed between distant parties and close to perfect quantum measurements, which is hardly achievable with current technology. Notwithstanding, recent theoretical and experimental efforts have led to proof-of-principle DI-QKD implementations. In this article, we review the state-of-the-art of DI-QKD by highlighting its main theoretical and experimental achievements, discussing recent proof-of-principle demonstrations, and emphasizing the existing challenges in the field.

  • Quantum vortices of strongly interacting photons

    Drori L., Das B. C., Zohar T. D., Winer G., Poem E., Poddubny A. & Firstenberg O. (2023) Science (New York, N.Y.).
    Vortices are topologically nontrivial defects that generally originate from nonlinear field dynamics. All-optical generation of photonic vortices-phase singularities of the electromagnetic field-requires sufficiently strong nonlinearity that is typically achieved in the classical optics regime. We report on the realization of quantum vortices of photons that result from a strong photon-photon interaction in a quantum nonlinear optical medium. The interaction causes faster phase accumulation for copropagating photons, producing a quantum vortex-antivortex pair within the two-photon wave function. For three photons, the formation of vortex lines and a central vortex ring confirms the existence of a genuine three-photon interaction. The wave function topology, governed by two- and three-photon bound states, imposes a conditional phase shift of π per photon, a potential resource for deterministic quantum logic operations.

  • Improved laser phase locking with intra-cavity adaptive optics

    Pando A., Gadasi S., Friesem A. & Davidson N. (2023) Optics Express.
    Phase locking of coupled lasers is severely hindered by the spread in their natural lasing frequencies. We present an intra-cavity adaptive optics method that reduces the frequency spread and thereby improves phase locking. Using an intra-cavity spatial light modulator and an iterative optimization algorithm, we demonstrate a fourfold enhancement of phase locking 450 coupled lasers, as quantified by the peak intensity and the inverse participation ratio of the far-field output distributions. We further show that the improvement is long-lasting, and suitable for phase locking of weakly coupled lasers.

  • Strongly interacting Bose-Fermi mixture: mediated interaction, phase diagram and sound propagation

    Shen X., Davidson N., Bruun G. M., Sun M. & Wu Z. (2023) arXiv.org.
    Motivated by recent surprising experimental findings, we develop a strong-coupling theory for Bose-Fermi mixtures capable of treating resonant inter-species interactions while satisfying the compressibility sum rule. We show that the mixture can be stable at large interaction strengths close to resonance, in agreement with the experiment but at odds with the widely used perturbation theory. We also calculate the sound velocity of the Bose gas in the 133Cs-6Li mixture, again finding good agreement with the experimental observations both at weak and strong interactions. A central ingredient of our theory is the generalization of a fermion mediated interaction to strong Bose-Fermi scatterings and to finite frequencies. This further leads to a predicted hybridization of the sound modes of the Bose and Fermi gases, which can be directly observed using Bragg spectroscopy.

  • Proton acceleration with intense twisted laser light

    Willim C., Vieira J., Malka V. & Silva L. O. (2023) Physical Review Research.
    An efficient approach that considers a high-intensity twisted laser of moderate energy (few J) is proposed to generate collimated proton bunches with multi-10 MeV energies from a double-layer hydrogen target. Three-dimensional particle-in-cell simulations demonstrate the formation of a highly collimated and energetic (∼40 MeV) proton bunch, whose divergence is ∼6.5 times smaller compared to the proton bunch driven by a Gaussian laser containing the same energy. Supported by theoretical modeling of relativistic self-focusing in near-critical plasma, we establish a regime that allows for consistent acceleration of high-energetic proton bunches with low divergence under experimentally feasible conditions for twisted drivers.

  • Nonlinear coherent heat machines

    Opatrný T., Bräuer Š., Kofman A. G., Misra A., Meher N., Firstenberg O., Poem E. & Kurizki G. (2023) Science advances.
    We propose heat machines that are nonlinear, coherent, and closed systems composed of few field (oscillator) modes. Their thermal-state input is transformed by nonlinear Kerr interactions into nonthermal (non-Gaussian) output with controlled quantum fluctuations and the capacity to deliver work in a chosen mode. These machines can provide an output with strongly reduced phase and amplitude uncertainty that may be useful for sensing or communications in the quantum domain. They are experimentally realizable in optomechanical cavities where photonic and phononic modes are coupled by a Josephson qubit or in cold gases where interactions between photons are transformed into dipole-dipole interacting Rydberg atom polaritons. This proposed approach is a step toward the bridging of quantum and classical coherent and thermodynamic descriptions.

  • Transition Metal Ion Ensembles in Crystals as Solid-State Coherent Spin-Photon Interfaces: The Case of Nickel in Magnesium Oxide

    Poem E., Gupta S., Morris I., Klink K., Singh L., Zhong T., Nicley S. S., Becker J. N. & Firstenberg O. (2023) PRX Quantum.
    We present general guidelines for finding solid-state systems that could serve as coherent electron-spin-photon interfaces even at relatively high temperatures, where phonons are abundant but cooling is easier, and show that transition-metal ions in various crystals could comply with these guidelines. As an illustrative example, we focus on divalent nickel ions in magnesium oxide. We perform electron-spin-resonance spectroscopy and polarization-sensitive magneto-optical fluorescence spectroscopy of a dense ensemble of these ions and find that (i) the ground-state electron spin stays coherent at liquid-helium temperatures for several microseconds and (ii) there exist energetically well-isolated excited states that can couple to two ground-state spin sublevels via optical transitions of orthogonal polarizations. The latter implies that fast coherent optical control over the electron spin is possible. We then propose schemes for optical initialization and control of the ground-state electron spin using polarized optical pulses, as well as two schemes for implementing a noise-free broadband quantum optical memory at near-telecom wavelengths in this material system.

  • Single-Photon Synchronization with a Room-Temperature Atomic Quantum Memory

    Davidson O., Yogev O., Poem E. & Firstenberg O. (2023) Physical review letters.
    Efficient synchronization of single photons that are compatible with narrow band atomic transitions is an outstanding challenge, which could prove essential for photonic quantum information processing. Here we report on the synchronization of independently generated single photons using a room-temperature atomic quantum memory. The photon source and the memory are interconnected by fibers and employ the same ladder-level atomic scheme. We store and retrieve the heralded single photons with end-to-end efficiency of η<sub>e2e</sub>=25% and final antibunching of g<sub>h</sub><sup>(2)</sup>=0.023. Our synchronization process results in an over tenfold increase in the photon-pair coincidence rate, reaching a rate of more than 1000 detected synchronized photon pairs per second. The indistinguishability of the synchronized photons is verified by a Hong-Ou-Mandel interference measurement.

  • Robust Two-Qubit Gates for Trapped Ions Using Spin-Dependent Squeezing

    Shapira Y., Cohen S., Akerman N., Stern A. & Ozeri R. (2023) Physical review letters.
    Entangling gates are an essential component of quantum computers. However, generating high-fidelity gates, in a scalable manner, remains a major challenge in all quantum information processing platforms. Accordingly, improving the fidelity and robustness of these gates has been a research focus in recent years. In trapped ions quantum computers, entangling gates are performed by driving the normal modes of motion of the ion chain, generating a spin-dependent force. Even though there has been significant progress in increasing the robustness and modularity of these gates, they are still sensitive to noise in the intensity of the driving field. Here we supplement the conventional spin-dependent displacement with spin-dependent squeezing, which creates a new interaction, that enables a gate that is robust to deviations in the amplitude of the driving field. We solve the general Hamiltonian and engineer its spectrum analytically. We also endow our gate with other, more conventional, robustness properties, making it resilient to many practical sources of noise and inaccuracies.

  • Energy-Conserving Theory of the Blowout Regime of Plasma Wakefield

    Golovanov A., Kostyukov I., Pukhov P. & Malka V. A. (2023) Physical review letters.
    We present a self-consistent theory of strongly nonlinear plasma wakefield (bubble or blowout regime of the wakefield) based on the energy conservation approach. Such wakefields are excited in plasmas by intense laser or particle beam drivers and are characterized by the expulsion of plasma electrons from the propagation axis of the driver. As a result, a spherical cavity devoid of electrons (called a “bubble”) and surrounded by a thin sheath made of expelled electrons is formed behind the driver. In contrast to the previous theoretical model [W. Lu et al., Phys. Rev. Lett. 96, 165002 (2006)], the presented theory satisfies the energy conservation law, does not require any external fitting parameters, and describes the bubble structure and the electromagnetic field it contains with much higher accuracy in a wide range of parameters. The obtained results are verified by 3D particle-in-cell simulations.

  • Coupling light to an atomic tweezer array in a cavity

    Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2023) arXiv.org.
    We consider the coupling of light, via an optical cavity, to two-dimensional atomic arrays whose lattice spacing exceeds the wavelength of the light. Such 'superwavelength' spacing is typical of optical tweezer arrays. While subwavelength arrays exhibit strong atom-photon coupling, characterized by high optical reflectivity in free space, the coupling efficiency of superwavelength arrays is reduced due to collective scattering losses to high diffraction orders. We show that a moderate-finesse cavity overcomes these losses. As the scattering losses peak at certain discrete values of the lattice spacing, the spacing can be optimized to achieve efficient atom-photon coupling in the cavity. Our cavity-QED theory properly accounts for collective dipolar interactions mediated by the lossy, non-cavity-confined photon modes and for finite-size effects of both the array and the light field. These findings pave the way to harnessing the versatility of tweezer arrays for efficient atom-photon interfaces in applications of quantum computing, networking, and nonlinear optics.

  • Interaction of light with matter: A coherent perspective

    Tannor D. J. (2023) .

  • Effect of fast noise on the fidelity of trapped-ion quantum gates

    Nakav H., Finkelstein R., Peleg L., Akerman N. & Ozeri R. (2023) Physical Review A.
    High-fidelity single- and multiqubit operations compose the backbone of quantum information processing. This fidelity is based on the ability to couple single- or two-qubit levels in an extremely coherent and precise manner. A necessary condition for coherent quantum evolution is a highly stable local oscillator driving these transitions. Here we study the effect of fast noise, that is, noise at frequencies much higher than the local oscillator linewidth, on the fidelity of one- and two-qubit gates in a trapped-ion system. We analyze and measure the effect of fast noise on single-qubit operations, including resonant π rotations and off-resonant sideband transitions. We further numerically analyze the effect of fast phase noise on the Mølmer-Sørensen two-qubit gate. We find a unified and simple way to estimate the performance of all of these operations through a single parameter given by the noise power spectral density at the qubit response frequency. While our analysis focuses on phase noise and on trapped-ion systems, it is relevant for other sources of fast noise as well as for other qubit systems in which spinlike qubits are coupled by a common bosonic field. Our analysis can help in guiding the design of quantum hardware platforms and gates, improving their fidelity towards fault-tolerant quantum computing.

  • Correlating Fluorescence Intermittency and Second‐Harmonic Generation in Single‐Colloidal Semiconductor Nanoplatelets

    Rosenberg M. & Oron D. (2023) Advanced photonics research.
    While most single-nanocrystal spectroscopy experiments rely on fluorescent emission, recent years have seen an increasing number of experiments based on absorption and scattering, enabling to correlate those with fluorescence intermittency. Herein, it is shown that nonlinear scattering by second-harmonic generation can also be measured from single CdSe/CdS core/shell nanoplatelets (NPLs) alongside fluorescence despite the weak scattering signal. It is shown that even under resonant two-photon conditions the second-harmonic scattering signal is uncorrelated with fluorescence intermittency and follows Poisson statistics.

  • Refractive plasma optics for relativistic laser beams

    Seemann O., Wan Y., Tata S., Kroupp E. & Malka V. (2023) Nature Communications.
    The high intensities reached today by powerful lasers enable us to explore the interaction with matter in the relativistic regime, unveiling a fertile domain of modern science that is pushing far away the frontiers of plasma physics. In this context, refractive-plasma optics are being utilized in well established wave guiding schemes in laser plasma accelerators. However, their use for spatial phase control of the laser beam has never been successfully implemented, partly due to the complication in manufacturing such optics. We here demonstrate this concept which enables phase manipulation near the focus position, where the intensity is already relativistic. Offering such flexible control, high-intensity high-density interaction is becoming accessible, allowing for example, to produce multiple energetic electron beams with high pointing stability and reproducibility. Cancelling the refractive effect with adaptive mirrors at the far field confirms this concept and furthermore improves the coupling of the laser to the plasma in comparison to the null test case, with potential benefits in dense-target applications.

  • Trap-assisted formation of atom–ion bound states

    Pinkas M., Katz O., Wengrowicz J., Akerman N. & Ozeri R. (2023) Nature Physics.
    The formation of molecules in binary particle collisions is forbidden in free space, but the presence of an external trapping potential now enables the realization of bound states in ultracold atom-ion collisions.Pairs of free particles cannot form bound states in an elastic collision due to momentum and energy conservation. In many ultracold experiments, however, the particles collide in the presence of an external trapping potential that can couple their centre-of-mass and relative motions, assisting the formation of bound states. Here we report the observation of weakly bound molecular states formed between one ultracold atom and a single trapped ion in the presence of a linear Paul trap. We show that bound states can efficiently form in binary collisions, and enhance the rate of inelastic processes. By measuring the electronic spin-exchange rate, we study the dependence of these bound states on the collision energy and magnetic field, and extract the average molecular binding energy and mean lifetime of the molecule, having good agreement with molecular dynamics simulations. Our simulations predict a power-law distribution of molecular lifetimes with a mean that is dominated by extreme, long-lived events. The dependence of the molecular properties on the trapping parameters enables further studies on the characterization and control of ultracold collisions.

  • Quantum sensing of electric field distributions of liquid electrolytes with NV-centers in nanodiamonds

    Hollendonner M., Sharma S., Parthasarathy S. K., Dasari D. B., Finkler A., Kusminskiy S. V. & Nagy R. (2023) New Journal of Physics.
    To use batteries as large-scale energy storage systems it is necessary to measure and understand their degradation in-situ and in-operando. As a battery’s degradation is often the result of molecular processes inside the electrolyte, a sensing platform which allows to measure the ions with a high spatial resolution is needed. Primary candidates for such a platform are NV-centers in diamonds. We propose to use a single NV-center to deduce the electric field distribution generated by the ions inside the electrolyte through microwave pulse sequences. We show that the electric field can be reconstructed with great accuracy by using a protocol which includes different variations of the free induction decay to obtain the mean electric field components and a pulse sequence consisting of three polarized π-pulses to measure the electric field’s standard deviation σ E . From a semi-analytical ansatz we find that for a lithium ion battery there is a direct relationship between σ E and the ionic concentration. Our results show that it is therefore possible to use NV-centers as sensors to measure both the electric field distribution and the local ionic concentration inside electrolytes.

  • Heralded Spectroscopy: a new single-particle probe for nanocrystal photophysics

    Lubin G., Tenne R., Ulku A. C., Antolovic I. M., Burri S., Karg S., Yallapragada V. J., Yaniv G., Kazes M., Amgar D., Frenkel N., Bruschini C., Charbon E. & Oron D. (2023) .
    Semiconductor nanocrystals feature multiply-excited states that display intriguing physics and significantly impact nanocrystal-based technologies. Fluorescence supplies a natural probe to investigate these states. Still, direct observation of multiexciton fluorescence has proved elusive to existing spectroscopy techniques. Heralded Spectroscopy is a new tool based on a breakthrough single-particle, single-photon, sub-nanosecond spectrometer that utilizes temporal photon correlations to isolate multiexciton emission. This proceedings paper introduces Heralded Spectroscopy and reviews some of the novel insights it uncovered into exciton–exciton interactions within single nanocrystals. These include weak exciton–exciton interactions and their correlation with quantum confinement, biexciton spectral diffusion, multiple biexciton species and biexciton emission polarization.

  • Seeded free-electron laser driven by a compact laser plasma accelerator

    Labat M., Cabadağ J. C., Ghaith A., Irman A., Berlioux A., Berteaud P., Blache F., Bock S., Bouvet F., Briquez F., Chang Y. Y., Corde S., Debus A., De Oliveira C., Duval J. P., Dietrich Y., El Ajjouri M., Eisenmann C., Gautier J., Gebhardt R., Grams S., Helbig U., Herbeaux C., Hubert N., Kitegi C., Kononenko O., Kuntzsch M., LaBerge M., Lê S., Leluan B., Loulergue A., Malka V., Marteau F., Guyen M. H. N., Oumbarek-Espinos D., Pausch R., Pereira D., Püschel T., Ricaud J. P., Rommeluere P., Roussel E., Rousseau P., Schöbel S., Sebdaoui M., Steiniger K., Tavakoli K., Thaury C., Ufer P., Valléau M., Vandenberghe M., Vétéran J., Schramm U. & Couprie M. E. (2023) Nature Photonics.
    Free-electron lasers generate high-brilliance coherent radiation at wavelengths spanning from the infrared to the X-ray domains. The recent development of short-wavelength seeded free-electron lasers now allows for unprecedented levels of control on longitudinal coherence, opening new scientific avenues such as ultra-fast dynamics on complex systems and X-ray nonlinear optics. Although those devices rely on state-of-the-art large-scale accelerators, advancements on laser-plasma accelerators, which harness gigavolt-per-centimetre accelerating fields, showcase a promising technology as compact drivers for free-electron lasers. Using such footprint-reduced accelerators, exponential amplification of a shot-noise type of radiation in a self-amplified spontaneous emission configuration was recently achieved. However, employing this compact approach for the delivery of temporally coherent pulses in a controlled manner has remained a major challenge. Here we present the experimental demonstration of a laser-plasma accelerator-driven free-electron laser in a seeded configuration, where control over the radiation wavelength is accomplished. Furthermore, the appearance of interference fringes, resulting from the interaction between the phase-locked emitted radiation and the seed, confirms longitudinal coherence. Building on our scientific achievements, we anticipate a navigable pathway to extreme-ultraviolet wavelengths, paving the way towards smaller-scale free-electron lasers, unique tools for a multitude of applications in industry, laboratories and universities.

  • Heisenberg-Langevin approach to driven superradiance

    Somech O., Shimshi Y. & Shahmoon E. (2023) Physical Review A.
    We present an analytical approach for the study of driven Dicke superradiance based on a Heisenberg-Langevin formulation. We calculate the steady-state fluctuations of both the atomic-spin and light-field operators. While the atoms become entangled below a critical drive, exhibiting spin squeezing, we show that the radiated light is in a classical-like coherent state whose amplitude and spectrum are identical to those of the incident driving field. Therefore, the nonlinear atomic system scatters light as a linear classical scatterer. Our results are consistent with the recent theory of coherently radiating spin states. The presented Heisenberg-Langevin approach should be simple to generalize for treating superradiance beyond the permutation-symmetric Dicke model.

  • OPENING UP HIGH-PERFORMANCE LASER SCIENCE TO THE WORLD AT THE EXTREME LIGHT INFRASTRUCTURE (ELI)

    Harrison A., Malka V., Margarone D. & Varjú K. (2023) Europhysics News.

  • Non-Hermitian optical design by coordinate transformations and mapping

    Kresic I., Makris K. G., Brandstötter A., Leonhardt U. & Rotter S. (2023) International Conference on Metamaterials, Photonic Crystals and Plasmonics.
    Coordinate transformations have been a powerful tool for design of metamaterial optical structures during the last 15 years [1]. In this talk I will discuss our recent research about theoretical methodologies for creating non-Hermitian transparent materials [2], invisibility cloaks [3], and light confinement [4], by coordinate transformations and mapping of electromagnetic field solutions.

  • The surface chemistry of ionic liquid-treated CsPbBr3 quantum dots

    Crans K. D., Bain M., Bradforth S. E., Oron D., Kazes M. & Brutchey R. L. (2023) Journal of Chemical Physics.
    The power conversion efficiencies of lead halide perovskite thin film solar cells have surged in the short time since their inception. Compounds, such as ionic liquids (ILs), have been explored as chemical additives and interface modifiers in perovskite solar cells, contributing to the rapid increase in cell efficiencies. However, due to the small surface area-to-volume ratio of the large grained polycrystalline halide perovskite films, an atomistic understanding of the interaction between ILs and perovskite surfaces is limited. Here, we use quantum dots (QDs) to study the coordinative surface interaction between phosphonium-based ILs and CsPbBr3. When native oleylammonium oleate ligands are exchanged off the QD surface with the phosphonium cation as well as the IL anion, a threefold increase in photoluminescent quantum yield of as-synthesized QDs is observed. The CsPbBr3 QD structure, shape, and size remain unchanged after ligand exchange, indicating only a surface ligand interaction at approximately equimolar additions of the IL. Increased concentrations of the IL lead to a disadvantageous phase change and a concomitant decrease in photoluminescent quantum yields. Valuable information regarding the coordinative interaction between certain ILs and lead halide perovskites has been elucidated and can be used for informed pairing of beneficial combinations of IL cations and anions.

  • Quantum light microscopy

    Bowen W. P., Chrzanowski H. M., Oron D., Ramelow S., Tabakaev D., Terrasson A. & Thew R. (2023) Contemporary Physics.
    Much of our progress in understanding microscale biology has been powered by advances in microscopy. For instance, super-resolution microscopes allow the observation of biological structures at near-atomic-scale resolution, while multi-photon microscopes allow imaging deep into tissue. However, biological structures and dynamics still often remain out of reach of existing microscopes, with further advances in signal-to-noise, resolution and speed needed to access them. In many cases, the performance of microscopes is now limited by quantum effects–such as noise due to the quantisation of light into photons or, for multi-photon microscopes, the low cross-section of multi-photon scattering. These limitations can be overcome by exploiting features of quantum mechanics such as entanglement. Quantum effects can also provide new ways to enhance the performance of microscopes, such as new super-resolution techniques and new techniques to image at difficult to reach wavelengths. This review provides an overview of these various ways in which quantum techniques can improve microscopy, including recent experimental progress. It seeks to provide a realistic picture of what is possible, and what the constraints and opportunities are.

  • Optimal control for maximally creating and maintaining a superposition state of a two-level system under the influence of Markovian decoherence

    Ohtsuki Y., Mikami S., Ajiki T. & Tannor D. J. (2023) Journal of the Chinese Chemical Society (Taipei).
    Reducing decoherence is an essential step toward realizing general-purpose quantum computers beyond the present noisy intermediate-scale quantum (NISQ) computers. To this end, dynamical decoupling (DD) approaches in which external fields are applied to qubits are often adopted. We numerically study DD using a two-level model system (qubit) under the influence of Markovian decoherence by using quantum optimal control theory with slightly modified settings, in which the physical objective is to maximally create and maintain a specified superposition state in a specified control period. An optimal pulse is numerically designed while systematically varying the values of dephasing, population decay, pulse fluence, and control period as well as using two kinds of objective functionals. The decrease in purity due to the decoherence limits the ability to maintain a coherent superposition state; we refer to the state of maximal purity that can be maintained as the saturated value. The optimally shaped pulse minimizes the negative effect of decoherence by gradually populating and continuously replenishing the state of saturated purity.

  • Benchmarking the optimization optical machines with the planted solutions

    Stroev N., Berloff N. G. & Davidson N. (2023) arXiv.org.
    We introduce universal, easy-to-reproduce generative models for the QUBO instances to differentiate the performance of the hardware/solvers effectively. Our benchmark process extends the well-known Hebb's rule of associative memory with the asymmetric pattern weights. We provide a comprehensive overview of calculations conducted across various scales and using different classes of dynamical equations. Our aim is to analyze their results, including factors such as the probability of encountering the ground state, planted state, spurious state, or states falling outside the predetermined energy range. Moreover, the generated problems show additional properties, such as the easy-hard-easy complexity transition and complicated cluster structures of planted solutions. Our method establishes a prospective platform to potentially address other questions related to the fundamental principles behind device physics and algorithms for novel computing machines.

  • Synchronization in coupled laser arrays with correlated and uncorrelated disorder

    Pando A., Gadasi S., Bernstein E., Stroev N., Friesem A. & Davidson N. (2023) arXiv.org.
    The effect of quenched disorder in a many-body system is experimentally investigated in a controlled fashion. It is done by measuring the phase synchronization (i.e. mutual coherence) of 400 coupled lasers as a function of tunable disorder and coupling strengths. The results reveal that correlated disorder has a non-trivial effect on the decrease of phase synchronization, which depends on the ratio of the disorder correlation length over the average size of synchronized clusters. The experimental results are supported by numerical simulations and analytic derivations.

  • Disequilibrating azobenzenes by visible-light sensitization under confinement

    Gemen J., Church J. R., Ruoko T. P., Durandin N., Białek M. J., Weißenfels M., Feller M., Kazes M., Odaybat M., Borin V. A., Kalepu R., Diskin-Posner Y., Oron D., Fuchter M. J., Priimagi A., Schapiro I. & Klajn R. (2023) Science (New York, N.Y.).
    Photoisomerization of azobenzenes from their stable E isomer to the metastable Z state is the basis of numerous applications of these molecules. However, this reaction typically requires ultraviolet light, which limits applicability. In this study, we introduce disequilibration by sensitization under confinement (DESC), a supramolecular approach to induce the E-to-Z isomerization by using light of a desired color, including red. DESC relies on a combination of a macrocyclic host and a photosensitizer, which act together to selectively bind and sensitize E-azobenzenes for isomerization. The Z isomer lacks strong affinity for and is expelled from the host, which can then convert additional E-azobenzenes to the Z state. In this way, the host-photosensitizer complex converts photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed through direct photoexcitation.

  • Entropy Accumulation under Post-Quantum Cryptographic Assumptions

    Merkulov I. & Arnon-Friedman R. (2023) arxiv.org.
    In device-independent (DI) quantum protocols, the security statements are oblivious to the characterization of the quantum apparatus - they are based solely on the classical interaction with the quantum devices as well as some well-defined assumptions. The most commonly known setup is the so-called non-local one, in which two devices that cannot communicate between themselves present a violation of a Bell inequality. In recent years, a new variant of DI protocols, that requires only a single device, arose. In this novel research avenue, the no-communication assumption is replaced with a computational assumption, namely, that the device cannot solve certain post-quantum cryptographic tasks. The protocols for, e.g., randomness certification, in this setting that have been analyzed in the literature used ad hoc proof techniques and the strength of the achieved results is hard to judge and compare due to their complexity. Here, we build on ideas coming from the study of non-local DI protocols and develop a modular proof technique for the single-device computational setting. We present a flexible framework for proving the security of such protocols by utilizing a combination of tools from quantum information theory, such as the entropic uncertainty relation and the entropy accumulation theorem. This leads to an insightful and simple proof of security, as well as to explicit quantitative bounds. Our work acts as the basis for the analysis of future protocols for DI randomness generation, expansion, amplification and key distribution based on post-quantum cryptographic assumptions.

  • Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules

    Frenkel N., Scharf E., Lubin G., Levi A., Panfil Y. E., Ossia Y., Planelles J., Climente J. I., Banin U. & Oron D. (2023) ACS Nano.
    Coupled colloidal quantum dot molecules (CQDMs) are an emerging class of nanomaterials, manifesting two coupled emission centers and thus introducing additional degrees of freedom for designing quantum-dot-based technologies. The properties of multiply excited states in these CQDMs are crucial to their performance as quantum light emitters, but they cannot be fully resolved by existing spectroscopic techniques. Here we study the characteristics of biexcitonic species, which represent a rich landscape of different configurations essentially categorized as either segregated or localized biexciton states. To this end, we introduce an extension of Heralded Spectroscopy to resolve the different biexciton species in the prototypical CdSe/CdS CQDM system. By comparing CQDMs with single quantum dots and with nonfused quantum dot pairs, we uncover the coexistence and interplay of two distinct biexciton species: A fast-decaying, strongly interacting biexciton species, analogous to biexcitons in single quantum dots, and a long-lived, weakly interacting species corresponding to two nearly independent excitons. The two biexciton types are consistent with numerical simulations, assigning the strongly interacting species to two excitons localized at one side of the quantum dot molecule and the weakly interacting species to excitons segregated to the two quantum dot molecule sides. This deeper understanding of multiply excited states in coupled quantum dot molecules can support the rational design of tunable single- or multiple-photon quantum emitters.

  • Quantum Simulations of Interacting Systems with Broken Time-Reversal Symmetry

    Shapira Y., Manovitz T., Akerman N., Stern A. & Ozeri R. (2023) Physical Review X.
    Many-body systems of quantum interacting particles in which time-reversal symmetry is broken give rise to a variety of rich collective behaviors and are, therefore, a major target of research in modern physics. Quantum simulators can potentially be used to explore and understand such systems, which are often beyond the computational reach of classical simulation. Of these, platforms with universal quantum control can experimentally access a wide range of physical properties. However, simultaneously achieving strong programmable interactions, strong time-reversal symmetry breaking, and high-fidelity quantum control in a scalable manner is challenging. Here, we realize quantum simulations of interacting, time-reversal-broken quantum systems in a universal trapped-ion quantum processor. Using a recently proposed, scalable scheme, we implement time-reversal-breaking synthetic gauge fields, shown for the first time in a trapped-ion chain, along with unique coupling geometries, potentially extendable to simulation of multidimensional systems. Our high-fidelity single-site resolution in control and measurement, along with highly programmable interactions, allow us to perform full state tomography of a ground state showcasing persistent current and to observe dynamics of a time-reversal-broken system with nontrivial interactions. Our results open a path toward simulation of time-reversal-broken many-body systems with a wide range of features and coupling geometries.

  • Real-time frequency estimation of a qubit without single-shot-readout

    Zohar I., Haylock B., Romach Y., Arshad M. J., Halay N., Drucker N., Stöhr R., Denisenko A., Cohen Y., Bonato C. & Finkler A. (2023) Quantum Science and Technology.
    Quantum sensors can potentially achieve the Heisenberg limit of sensitivity over a large dynamic range using quantum algorithms. The adaptive phase estimation algorithm (PEA) is one example that was proven to achieve such high sensitivities with single-shot readout (SSR) sensors. However, using the adaptive PEA on a non-SSR sensor is not trivial due to the low contrast nature of the measurement. The standard approach to account for the averaged nature of the measurement in this PEA algorithm is to use a method based on ‘majority voting’. Although it is easy to implement, this method is more prone to mistakes due to noise in the measurement. To reduce these mistakes, a binomial distribution technique from a batch selection was recently shown theoretically to be superior, as all ranges of outcomes from an averaged measurement are considered. Here we apply, for the first time, real-time non-adaptive PEA on a non-SSR sensor with the binomial distribution approach. We compare the mean square error of the binomial distribution method to the majority-voting approach using the nitrogen-vacancy center in diamond at ambient conditions as a non-SSR sensor. Our results suggest that the binomial distribution approach achieves better accuracy with the same sensing times. To further shorten the sensing time, we propose an adaptive algorithm that controls the readout phase and, therefore, the measurement basis set. We show by numerical simulation that adding the adaptive protocol can further improve the accuracy in a future real-time experiment.

  • Revealing the Interplay between Strong Field Selection Rules and Crystal Symmetries

    Uzan-Narovlansky A. J., Orenstein G., Shames S., Even Tzur M., Kneller O., Bruner B. D., Arusi-Parpar T., Cohen O. & Dudovich N. (2023) Physical review letters.
    Symmetries are ubiquitous in condensed matter physics, playing an important role in the appearance of different phases of matter. Nonlinear light matter interactions serve as a coherent probe for resolving symmetries and symmetry breaking via their link to selection rules of the interaction. In the extreme nonlinear regime, high harmonic generation (HHG) spectroscopy offers a unique spectroscopic approach to study this link, probing the crystal spatial properties with high sensitivity while opening new paths for selection rules in the XUV regime. In this Letter we establish an advanced HHG polarimetry scheme, driven by a multicolor strong laser field, to observe the structural symmetries of solids and their interplay with the HHG selection rules. By controlling the crystal symmetries, we resolve nontrivial polarization states associated with new spectral features in the HHG spectrum. Our scheme opens new opportunities in resolving the symmetries of quantum materials, as well as ultrafast light driven symmetries in condensed matter systems.

  • A-Site Cation Dependence of Self-Healing in Polycrystalline APbI<sub>3</sub> Perovskite Films

    Singh P., Soffer Y., Ceratti D. R., Elbaum M., Oron D., Hodes G. & Cahen D. (2023) ACS Energy Letters.
    In terms of sustainable use, halide perovskite (HaP) semiconductors have a strong advantage over most other classes of materials for (opto)electronics, as they can self-heal (SH) from photodamage. While there is considerable literature on SH in devices, where it may not be clear exactly where damage and SH occur, there is much less on the HaP material itself. Here we perform “fluorescence recovery after photobleaching” (FRAP) measurements to study SH on polycrystalline thin films for which encapsulation is critical to achieving complete and fast self-healing. We compare SH in three photoactive APbI<sub>3</sub> perovskite films by varying the A-site cation ranging from (relatively) small inorganic Cs through medium-sized MA to large FA (the last two are organic cations). While the A cation is often considered electronically relatively inactive, it significantly affects both SH kinetics and the threshold for photodamage. The SH kinetics are markedly faster for γ-CsPbI<sub>3</sub> and α-FAPbI<sub>3</sub> than for MAPbI<sub>3</sub>. Furthermore, γ-CsPbI<sub>3</sub> exhibits an intricate interplay between photoinduced darkening and brightening. We suggest possible explanations for the observed differences in SH behavior. This study’s results are essential for identifying absorber materials that can regain intrinsic, insolation-induced photodamage-linked efficiency loss during its rest cycles, thus enabling applications such as autonomously sustainable electronics.

  • Control of electron beam current, charge, and energy spread using density downramp injection in laser wakefield accelerators

    Hue C. S., Wan Y., Levine E. Y. & Malka V. (2023) Matter and Radiation at Extremes.
    Density downramp injection has been demonstrated to be an elegant and efficient approach for generating high-quality electron beams in laser wakefield accelerators. Recent studies have demonstrated the possibilities of generating electron beams with charges ranging from tens to hundreds of picocoulombs while maintaining good beam quality. However, the plasma and laser parameters in these studies have been limited to specific ranges or attention has been focused on separate physical processes such as beam loading, which affects the uniformity of the accelerating field and thus the energy spread of the trapped electrons, the repulsive force from the rear spike of the bubble, which reduces the transverse momentum p⊥ of the trapped electrons and results in small beam emittance, and the laser evolution when traveling in the plasma. In this work, we present a comprehensive numerical study of downramp injection in the laser wakefield, and we demonstrate that the current profile of the injected electron beam is directly correlated with the density transition parameters, which further affects the beam charge and energy evolution. By fine-tuning the plasma density parameters, electron beams with high charge (up to several hundreds of picocoulombs) and low energy spread (around 1% FWHM) can be obtained. All these results are supported by large-scale quasi-three-dimensional particle-in-cell simulations. We anticipate that the electron beams with tunable beam properties generated using this approach will be suitable for a wide range of applications.

  • Robustness of Bell violation of graph states to qubit loss

    Silberstein S. & Arnon-Friedman R. (2023) Physical Review Research.
    Graph states are special entangled states advantageous for many quantum technologies, including quantum error correction, multiparty quantum communication, and measurement-based quantum computation. Yet, their fidelity is often disrupted by various errors, most notably qubit loss. In general, given an entangled state, Bell inequalities can be used to certify whether quantum entanglement remains despite errors. Here, we study the robustness of graph states to loss in terms of their Bell violation. Considering the recently proposed linearly scalable Bell operators by Baccari et al. [Phys. Rev. Lett. 124, 020402 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.020402], we use the stabilizer formalism to derive a formula for the extent by which the Bell violation of a given graph state is decreased with qubit loss. Our analysis allows one to determine which graph topologies are tolerable to qubit loss as well as pinpointing the Achilles' heel of each graph, namely the sets of qubits whose loss jeopardizes the Bell violation. Our results serve as an analytical tool for optimizing experiments and protocols involving graph states in realistically lossy systems. An experimental demonstration of a Bell violation in our noise-tolerant graphs is within reach using state of the art technology.

  • Epitaxial 2D PbS Nanosheet-Formamidinium Lead Triiodide Heterostructure Enabling High-Performance Perovskite Solar Cells

    Liu X., Wu Z., Zhong H., Wang X., Yang J., Zhang Z., Han J., Oron D. & Lin H. (2023) Advanced Functional Materials.
    Nanomaterials such as quantum dots and 2D materials have been widely used to improve the performance of perovskite solar cells due to their favorable optical properties, conductivity, and stability. Nevertheless, the interfacial crystal structures between perovskites and nanomaterials have always been ignored while large mismatches can result in a significant number of defects within solar cells. In this work, cubic PbS nanosheets with (200) preferred crystal planes are synthesized through anisotropy growth. Based on the similar crystal structure between cubic PbS (200) and cubic-phase formamidinium lead triiodide (alpha-FAPbI(3)) (200), a nanoepitaxial PbS nanosheets-FAPbI(3) heterostructure with low defect density is observed. Attribute to the epitaxial growth, PbS nanosheets-FAPbI(3) hybrid polycrystalline films show decreased defects and better crystallization. Optimized perovskite solar cells perform both improved efficiency and stability, retaining 90% of initial photovoltaic conversion efficiency after being stored at 20 degrees C and 20% RH for 2500 h. Notably, the significantly improved stability is ascribed to the interfacial compression strain and chemical bonding between (200) planes of PbS nanosheets and alpha-FAPbI(3) (200). This study provides insight into high-performance perovskite solar cells achieved by manipulating nanomaterial surfaces.

  • Superconducting Cavity Qubit with Tens of Milliseconds Single-Photon Coherence Time

    Milul O., Guttel B., Goldblatt U., Hazanov S., Joshi L. M., Chausovsky D., Kahn N., Çiftyürek E., Lafont F. & Rosenblum S. (2023) PRX Quantum.
    Storing quantum information for an extended period of time is essential for running quantum algorithms with low errors. Currently, superconducting quantum memories have coherence times of a few milliseconds, and surpassing this performance has remained an outstanding challenge. In this work, we report a single-photon qubit encoded in a novel superconducting cavity with a coherence time of 34 ms, representing an order of magnitude improvement compared to previous demonstrations. We use this long-lived quantum memory to store a Schrödinger cat state with a record size of 1024 photons, indicating the cavity's potential for bosonic quantum error correction.

  • Femtosecond electron microscopy of relativistic electron bunches

    Wan Y., Tata S., Seemann O., Levine E. Y., Smartsev S., Kroupp E. & Malka V. (2023) Light: Science and Applications.
    The development of plasma-based accelerators has enabled the generation of very high brightness electron bunches of femtosecond duration, micrometer size and ultralow emittance, crucial for emerging applications including ultrafast detection in material science, laboratory-scale free-electron lasers and compact colliders for high-energy physics. The precise characterization of the initial bunch parameters is critical to the ability to manipulate the beam properties for downstream applications. Proper diagnostic of such ultra-short and high charge density laser-plasma accelerated bunches, however, remains very challenging. Here we address this challenge with a novel technique we name as femtosecond ultrarelativistic electron microscopy, which utilizes an electron bunch from another laser-plasma accelerator as a probe. In contrast to conventional microscopy of using very low-energy electrons, the femtosecond duration and high electron energy of such a probe beam enable it to capture the ultra-intense space-charge fields of the investigated bunch and to reconstruct the charge distribution with very high spatiotemporal resolution, all in a single shot. In the experiment presented here we have used this technique to study the shape of a laser-plasma accelerated electron beam, its asymmetry due to the drive laser polarization, and its beam evolution as it exits the plasma. We anticipate that this method will significantly advance the understanding of complex beam-plasma dynamics and will also provide a powerful new tool for real-time optimization of plasma accelerators.

  • Rapid and robust quantum logic gates using inertial STIRAP

    Turyansky D., Ovdat O., Dann R., Kosloff R., Dayan B. & Pick A. (2023) .
    We present an inertial protocol for STIRAP-based single- and two-qubit quantum logic gates. Our protocol achieves an order-of-magnitude lower infidelity compared to existing protocols. A similar approach can be used to improve any adiabatic protocol.

  • Improved phase-locking of laser arrays by pump shaping

    Gadasi S., Bernstein E., Pando A., Friesem A. & Davidson N. (2023) Optics Express.
    We introduce a method to enhance the phase-locking quality and duration of an end-pumped laser array by precisely shaping its pump beam to overlap with the array. Shaping the pump beam results in a significant improvement in lasing efficiency and reduces the pump power required to reach the lasing threshold compared to a typical uniform pumping configuration. Our approach involves shaping a highly incoherent laser beam by addressing smaller segments of the beam with higher local spatial coherence. We demonstrate a remarkable increase in the laser array output brightness by up to a factor of 10, accompanied by a substantial extension in the phase-locking duration.

  • A practical guide to electromagnetically induced transparency in atomic vapor

    Finkelstein R., Bali S., Firstenberg O. & Novikova I. (2023) New Journal of Physics.
    This tutorial introduces the theoretical and experimental basics of electromagnetically induced transparency (EIT) in thermal alkali vapors. We first give a brief phenomenological description of EIT in simple three-level systems of stationary atoms and derive analytical expressions for optical absorption and dispersion under EIT conditions. Then we focus on how the thermal motion of atoms affects various parameters of the EIT system. Specifically, we analyze the Doppler broadening of optical transitions, ballistic versus diffusive atomic motion in a limited-volume interaction region, and collisional depopulation and decoherence. Finally, we discuss the common trade-offs important for optimizing an EIT experiment and give a brief ‘walk-through’ of a typical EIT experimental setup. We conclude with a brief overview of current and potential EIT applications.

  • Coherent manipulation of nuclear spins in the strong driving regime

    Yudilevich D., Salhov A., Schaefer I., Herb K., Retzker A. & Finkler A. (2023) New Journal of Physics.
    Spin-based quantum information processing makes extensive use of spin-state manipulation. This ranges from dynamical decoupling of nuclear spins in quantum sensing experiments to applying logical gates on qubits in a quantum processor. Fast manipulation of spin states is highly desirable for accelerating experiments, enhancing sensitivity, and applying elaborate pulse sequences. Strong driving using intense radio-frequency (RF) fields can, therefore, facilitate fast manipulation and enable broadband excitation of spin species. In this work, we present an antenna for strong driving in quantum sensing experiments and theoretically address challenges of the strong driving regime. First, we designed and implemented a micron-scale planar spiral RF antenna capable of delivering intense fields to a sample. The planar antenna is tailored for quantum sensing experiments using the diamond’s nitrogen-vacancy (NV) center and should be applicable to other solid-state defects. The antenna has a broad bandwidth of 22 MHz, is compatible with scanning probes, and is suitable for cryogenic and ultrahigh vacuum conditions. We measure the magnetic field induced by the antenna and estimate a field-to-current ratio of 113 ± 16 G/A, representing a six-fold increase in efficiency compared to the state-of-the-art, crucial for cryogenic experiments. We demonstrate the antenna by driving Rabi oscillations in <sup>1</sup>H spins of an organic sample on the diamond surface and measure <sup>1</sup>H Rabi frequencies of over 500 kHz, i.e. π -pulses shorter than 1 μ s —an order of magnitude faster than previously reported in NV-based nuclear magnetic resonance (NMR). Finally, we discuss the implications of driving spins with a field tilted from the transverse plane in a regime where the driving amplitude is comparable to the spin-state splitting, such that the rotating wave approximation does not describe the dynamics well. We present a simple recipe to optimize pulse fidelity in this regime based on a phase and offset-shifted sine drive, which may be optimized in situ without numerical optimization procedures or precise modeling of the experiment. We consider this approach in a range of driving amplitudes and show that it is particularly efficient in the case of a tilted driving field. The results presented here constitute a foundation for implementing fast nuclear spin control in various systems.

  • Ionization-induced long-lasting orientation of symmetric-top molecules

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2023) Physical Review A.
    We theoretically consider the phenomenon of field-free long-lasting orientation of symmetric-top molecules ionized by two-color laser pulses. The anisotropic ionization produces a significant long-lasting orientation of the surviving neutral molecules. The degree of orientation increases with both the pulse intensity and counterintuitively with the rotational temperature. The orientation may be enhanced even further by using multiple-delayed two-color pulses. The long-lasting orientation may be probed by even harmonic generation or by Coulomb-explosion-based methods. The effect may enable the study of relaxation processes in dense molecular gases and may be useful for molecular guiding and trapping by inhomogeneous fields.

  • Van der Waals chain: A simple model for Casimir forces in dielectrics

    Hörner H., Rachbauer L. M., Rotter S. & Leonhardt U. (2023) Physical Review B.
    The Casimir force between dielectric bodies is well-understood, but not the Casimir force inside a dielectric, in particular its renormalization. We develop and analyze a simple model for the Casimir forces inside a medium that is completely free of renormalization and show then how renormalization emerges. We consider a one-dimensional chain of point particles interacting with each other by scattering the zero-point fluctuations of the electromagnetic field confined to one dimension. We develop a fast, efficient algorithm for calculating the forces on each particle and apply it to study the macroscopic limit of infinitely many, infinitely weak scatterers. The force density converges for piecewise homogeneous media but diverges in inhomogeneous media, which would cause instant collapse in theory. We argue that short-range counterforces in the medium prevent this collapse in reality. Their effect appears as the renormalization of the Casimir stress in dielectrics. Our simple model also allows us to derive an elementary analog of the trace anomaly of quantum fields in curved space.

  • A look under the tunnelling barrier via attosecond-gated interferometry

    Kneller O., Azoury D., Federman Y., Krueger M., Uzan A. J., Orenstein G., Bruner B. D., Smirnova O., Patchkovskii S., Ivanov M. & Dudovich N. (2022) Nature Photonics.
    Interferometry has been at the heart of wave optics since its early stages, resolving the coherence of the light field and enabling the complete reconstruction of the optical information it encodes. Transferring this concept to the attosecond time domain shed new light on fundamental ultrafast electron phenomena. Here we introduce attosecond-gated interferometry and probe one of the most fundamental quantum mechanical phenomena, field-induced tunnelling. Our experiment probes the evolution of an electronic wavefunction under the tunnelling barrier and records the phase acquired by an electron as it propagates in a classically forbidden region. We identify the quantum nature of the electronic wavepacket and capture its evolution within the optical cycle. Attosecond-gated interferometry has the potential to reveal the underlying quantum dynamics of strong-field-driven atomic, molecular and solid-state systems.

  • Work extraction from single-mode thermal noise by measurements: How important is information?

    Misra A., Opatrny T. & Kurizki G. (2022) Physical Review. E.
    Our goal in this article is to elucidate the rapport of work and information in the context of a minimal quantum-mechanical setup: a converter of heat input to work output, the input consisting of a single oscillator mode prepared in a hot thermal state along with a few much colder oscillator modes. The core issues we consider, taking account of the quantum nature of the setup, are as follows: (i) How and to what extent can information act as a work resource or, conversely, be redundant for work extraction? (ii) What is the optimal way of extracting work via information acquired by measurements? (iii) What is the bearing of information on the efficiency-power tradeoff achievable in such setups? We compare the efficiency of work extraction and the limitations of power in our minimal setup by different, generic, measurement strategies of the hot and cold modes. For each strategy, the rapport of work and information extraction is found and the cost of information erasure is allowed for. The possibilities of work extraction without information acquisition, via nonselective measurements, are also analyzed. Overall, we present, by generalizing a method based on optimized homodyning that we have recently proposed, the following insight: extraction of work by observation and feedforward that only measures a small fraction of the input is clearly advantageous to the conceivable alternatives. Our results may become the basis of a practical strategy of converting thermal noise to useful work in optical setups, such as coherent amplifiers of thermal light, as well as in their optomechanical and photovoltaic counterparts.

  • Super-resolved second harmonic generation imaging by coherent image scanning microscopy

    Raanan D., Song M. S., Tisdale W. A. & Oron D. (2022) Applied Physics Letters.
    We extend image scanning microscopy to second harmonic generation (SHG) by extracting the complex field amplitude of the second-harmonic beam. While the theory behind coherent image scanning microscopy (ISM) is known, an experimental demonstration was not yet established. The main reason is that the naive intensity-reassignment procedure cannot be used for coherent scattering as the point spread function is now defined for the field amplitude rather than for the intensity. We use an inline interferometer to demonstrate super-resolved phase-sensitive SHG microscopy by applying the ISM reassignment machinery on the resolved field. This scheme can be easily extended to third harmonic generation and stimulated Raman microscopy schemes.

  • Optimal Selective Orientation of Chiral Molecules Using Femtosecond Laser Pulses

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) ArXiv.org..
    We present a comprehensive study of enantioselective orientation of chiral molecules excited by a pair of delayed cross-polarized femtosecond laser pulses. We show that by optimizing the pulses' parameters, a significant (~ 10%) degree of enantioselective orientation can be achieved at zero and at five kelvin rotational temperatures. This study suggests a set of reasonable experimental conditions for inducing and measuring strong enantioselective orientation. The strong enantioselective orientation and the wide availability of the femtosecond laser systems required for the proposed experiments may open new avenues for discriminating and separating molecular enantiomers.

  • Phase locking of lasers with Gaussian coupling

    Reddy A. N. K., Mahler S., Goldring A., Pal V., Friesem A. A. & Davidson N. (2022) Optics Express.
    A unique approach for steady in-phase locking of lasers in an array, regardless of the array geometry, position, orientation, period or size, is presented. The approach relies on the insertion of an intra-cavity Gaussian aperture in the far-field plane of the laser array. Steady in-phase locking of 90 lasers, whose far-field patterns are comprised of sharp spots with extremely high power density, was obtained for various array geometries, even in the presence of near-degenerate solutions, geometric frustration or superimposed independent longitudinal modes. The internal phase structures of the lasers can also be suppressed so as to obtain pure Gaussian mode laser outputs with uniform phase and overall high beam quality. With such phase locking, the laser array can be focused to a sharp spot of high power density, useful for many applications and the research field.

  • Visualizing Coherent Molecular Rotation in a Gaseous Medium [1, 2]

    Tutunnikov I., Prost E., Steinitz U., Béjot P., Hertz E., Billard F., Faucher O. & Averbukh I. S. (2022) .
    We present a study of a non-intrusive optical scheme for visualizing the rotational dynamics in an anisotropic molecular gas. The proposed optical method is promising for visualizing the rotations of symmetric- and asymmetric-top molecules.

  • Quantum Interface for Noble-Gas Spins Based on Spin-Exchange Collisions

    Katz O., Shaham R. & Firstenberg O. (2022) PRX Quantum.
    An ensemble of noble-gas nuclear spins is a unique quantum system that could maintain coherence for many hours at room temperature and above, owing to exceptional isolation from the environment. This isolation, however, is a mixed blessing, limiting the ability of these ensembles to interface with other quantum systems coherently. Here we show that spin-exchange collisions with alkali-metal atoms render a quantum interface for noble-gas spins without impeding their long coherence times. We formulate the many-body theory of the hybrid system and reveal a collective mechanism that strongly couples the macroscopic quantum states of the two spin ensembles. Despite their stochastic and random nature, weak collisions enable entanglement and reversible exchange of nonclassical excitations in an efficient, controllable, and deterministic process. With recent experiments now entering the strong-coupling regime, this interface paves the way toward realizing hour-long quantum memories and entanglement at room temperature.

  • Axiparabola: A new tool for high-intensity optics

    Oubrerie K., Andriyash I. A., Lahaye R., Smartsev S., Malka V. & Thaury C. (2022) Journal of Optics (United Kingdom).
    An axiparabola is a reflective aspherical optics that focuses a light beam into an extended focal line. The light intensity and group velocity profiles along the focus are adjustable through the proper design. The on-axis light velocity can be controlled, for instance, by adding spatio-temporal couplings via chromatic optics on the incoming beam. Therefore the energy deposition along the axis can be either subluminal or superluminal as required in various applications. This article first explores how the axiparabola design defines its properties in the geometric optics approximation. Then the obtained description is considered in numerical simulations for two cases of interest for laser-plasma acceleration. We show that the axiparabola can be used either to generate a plasma waveguide to overcome diffraction or for driving a dephasingless wakefield accelerator.

  • Thermodynamics and control of open quantum systems

    Kurizki G. & Kofman A. G. (2022) .
    The control of open quantum systems and their associated quantum thermodynamic properties is a topic of growing importance in modern quantum physics and quantum chemistry research. This unique and self-contained book presents a unifying perspective of such open quantum systems, first describing the fundamental theory behind these formidably complex systems, before introducing the models and techniques that are employed to control their quantum thermodynamics processes. A detailed discussion of real quantum devices is also covered, including quantum heat engines and quantum refrigerators. The theory of open quantum systems is developed pedagogically, from first principles, and the book is accessible to graduate students and researchers working in atomic physics, quantum information, condensed matter physics, and quantum chemistry.

  • Does Decoherence Select the Pointer Basis of a Quantum Meter?

    Kofman A. G. & Kurizki G. (2022) Entropy (Basel, Switzerland).
    The consensus regarding quantum measurements rests on two statements: (i) von Neumann's standard quantum measurement theory leaves undetermined the basis in which observables are measured, and (ii) the environmental decoherence of the measuring device (the "meter") unambiguously determines the measuring ("pointer") basis. The latter statement means that the environment (measures) observables of the meter and (indirectly) of the system. Equivalently, a measured quantum state must end up in one of the "pointer states" that persist in the presence of the environment. We find that, unless we restrict ourselves to projective measurements, decoherence does not necessarily determine the pointer basis of the meter. Namely, generalized measurements commonly allow the observer to choose from a multitude of alternative pointer bases that provide the same information on the observables, regardless of decoherence. By contrast, the measured observable does not depend on the pointer basis, whether in the presence or in the absence of decoherence. These results grant further support to our notion of Quantum Lamarckism, whereby the observer's choices play an indispensable role in quantum mechanics.

  • Minimal quantum thermal machine in a bandgap environment: non-Markovian features and anti-Zeno advantage

    Xu M., Stockburger J. T., Kurizki G. & Ankerhold J. (2022) New Journal of Physics.
    A minimal model of a quantum thermal machine is analyzed, where a driven two level working medium (WM) is embedded in an environment (reservoir) whose spectrum possesses bandgaps. The transition frequency of the WM is periodically modulated so as to be in alternating spectral overlap with hot or cold reservoirs whose spectra are separated by a bandgap. Approximate and exact treatments supported by analytical considerations yield a complete characterization of this thermal machine in the deep quantum domain. For slow to moderate modulation, the spectral response of the reservoirs is close to equilibrium, exhibiting sideband (Floquet) resonances in the heat currents and power output. In contrast, for faster modulation, strong-coupling and non-Markovian features give rise to correlations between the WM and the reservoirs and between the two reservoirs. Power boost of strictly quantum origin ('quantum advantage') is then found for both continuous and segmental fast modulation that leads to the anti-Zeno effect of enhanced spectral reservoir response. Such features cannot be captured by standard Markovian treatments.

  • Quantum logic detection of collisions between single atom-ion pairs

    Katz O., Pinkas M., Akerman N. & Ozeri R. (2022) Nature Physics.
    Studies of interactions between a single pair of atoms in a quantum state are a corner-stone of quantum chemistry, yet the number of demonstrated techniques that enable the observation and control of the outcome of a single collision is still small. Here we demonstrate a technique to study interactions between an ultracold neutral atom and a cold ion using quantum logic. We measure the inelastic release of hyperfine energy in a collision between an ultracold rubidium atom and isotopes of singly ionized strontium that we do not have experimental control over. We detect the collision outcome and measure the inelastic rate of the chemistry ion by reading the motional state of a logic ion qubit in a single shot. Our work extends the toolbox for studying elastic, inelastic and reactive chemical processes with existing experimental tools, especially for atomic and molecular ions for which direct laser cooling and state detection are unavailable.

  • Echo-enhanced molecular orientation at high temperatures

    Tutunnikov I., Xu L., Prior Y. & Averbukh I. S. (2022) Physical review. A..
    We consider the orientation of linear and symmetric-top molecules induced by laser and delayed terahertz (THz) pulses at high rotational temperatures (up to room temperature). We introduce an echo-assisted approach in which the achieved transient molecular orientation is an order of magnitude higher than the orientation produced by a single THz pulse. The laser pulse first dissects the wide molecular phase-space distribution into multiple narrow strips (filaments), each being cold and evolving separately. A subsequent THz pulse causes a substantial transient orientation of the individual filaments, which leads to an enhanced orientation of the whole molecular ensemble at later times via the echo mechanism. This enhanced degree of orientation is important in attosecond science, chemical reaction control, ultrafast molecular imaging, and other domains of physics.

  • Casimir cosmology

    Leonhardt U. (2022) International Journal of Modern Physics A.
    In 1998, astronomers discovered that the expansion of the universe is accelerating. Somehow, something must have made gravity repulsive on cosmological scales. This something was called dark energy; it is described by Einstein's cosmological constant; and it amounts to about 70% of the total mass of the universe. It has been conjectured that the cosmological constant is a form of vacuum energy, but its prediction from quantum field theory has failed by many orders of magnitude, until recently. Informed by empirical evidence on Casimir forces, Lifshitz theory has not only produced the correct order of magnitude, but is quantitatively consistent with the astronomical data. Moreover, the theory appears to resolve the tension between the measured and the predicted Hubble constant. There is therefore a good chance that Casimir physics explains dark energy. This paper introduces cosmology for practitioners of vacuum forces as part of "The State of the Quantum Vacuum: Casimir Physics in the 2020s"edited by K. A. Milton. It may also be interesting for other physicists and engineers who wish to have a concise introduction to cosmology.

  • Chiral States in Coupled-Lasers Lattice by On-Site Complex Potential

    Gadasi S., Arwas G., Gershenzon I., Friesem A. & Davidson N. (2022) Physical review letters.
    The ability to control the chirality of physical devices is of great scientific and technological importance, from investigations of topologically protected edge states in condensed matter systems to wavefront engineering, isolation, and unidirectional communication. When dealing with large networks of oscillators, the control over the chirality of the bulk states becomes significantly more complicated and requires complex apparatus for generating asymmetric coupling or artificial gauge fields. Here we present a new approach for a precise control over the chirality of the bulk state of a triangular array of hundreds of symmetrically coupled lasers, by introducing a weak non-Hermitian complex potential, requiring only local on-site control of loss and frequency. In the unperturbed network, lasing supermodes with opposite chirality (staggered vortex and staggered antivortex) are equally probable. We show that by tuning the complex potential to an exceptional point, a nearly pure chiral lasing supermode is achieved. While our approach is applicable to any oscillators network, we demonstrate how the inherent nonlinearity of the lasers effectively pulls the network to the exceptional point, making the chirality extremely resilient against noise and imperfections.

  • Gradient-based reconstruction of molecular Hamiltonians and density matrices from time-dependent quantum observables

    Zhang W., Tutunnikov I., Averbukh I. S. & Krems R. V. (2022) Physical Review A.
    We consider a quantum system with a time-independent Hamiltonian parametrized by a set of unknown parameters α. The system is prepared in a general quantum state by an evolution operator that depends on a set of unknown parameters P. After the preparation, the system evolves in time, and it is characterized by a time-dependent observable O(t). We show that it is possible to obtain closed-form expressions for the gradients of the distance between O(t) and a calculated observable with respect to α, P, and all elements of the system density matrix, whether for pure or mixed states. These gradients can be used in projected gradient descent to infer α, P, and the relevant density matrix from dynamical observables. We combine this approach with random phase wave function approximation to obtain closed-form expressions for gradients that can be used to infer population distributions from averaged time-dependent observables in problems with a large number of quantum states participating in dynamics. The approach is illustrated by determining the temperature of molecular gas (initially, in thermal equilibrium at room temperature) from laser-induced time-dependent molecular alignment.

  • Direct reconstruction of the band structure of a one-dimensional optical lattice with thermal atoms

    Courvoisier A., Gadge A. & Davidson N. (2022) Physical review. A.
    We report on a simple method to reconstruct the band structure of a one-dimensional optical lattice using a thermal cloud with a momentum spread of about two photon recoils. We image the momentum distribution of a thermal cloud exposed to a standing-wave potential using time-of-flight absorption images and observe unique features. With the support of numerical calculations, we explain their appearance and show how they can be used to reconstruct the full band structure directly. While this can serve as a precise lattice depth calibration tool, we additionally propose a method to estimate the lattice depth in a single-shot manner.

  • Roadmap on multimode light shaping

    Piccardo M., Ginis V., Forbes A., Mahler S., Friesem A. A., Davidson N., Ren H., Dorrah A. H., Capasso F., Dullo F. T., Ahluwalia B. S., Ambrosio A., Gigan S., Treps N., Hiekkamäki M., Fickler R., Kues M., Moss D., Morandotti R., Riemensberger J., Kippenberg T. J., Faist J., Scalari G., Picqué N., Hänsch T. W., Cerullo G., Manzoni C., Lugiato L. A., Brambilla M., Columbo L., Gatti A., Prati F., Shiri A., Abouraddy A. F., Alù A., Galiffi E., Pendry J. B. & Huidobro P. A. (2022) Journal of optics (2010).
    Our ability to generate new distributions of light has been remarkably enhanced in recent years. At the most fundamental level, these light patterns are obtained by ingeniously combining different electromagnetic modes. Interestingly, the modal superposition occurs in the spatial, temporal as well as spatio-temporal domain. This generalized concept of structured light is being applied across the entire spectrum of optics: generating classical and quantum states of light, harnessing linear and nonlinear light-matter interactions, and advancing applications in microscopy, spectroscopy, holography, communication, and synchronization. This Roadmap highlights the common roots of these different techniques and thus establishes links between research areas that complement each other seamlessly. We provide an overview of all these areas, their backgrounds, current research, and future developments. We highlight the power of multimodal light manipulation and want to inspire new eclectic approaches in this vibrant research community.

  • Ultra-high dose rate radiation production and delivery systems intended for FLASH

    Farr J., Grilj V., Malka V., Sudharsan S. & Schippers M. (2022) Medical physics (Lancaster).
    Higher dose rates, a trend for radiotherapy machines, can be beneficial in shortening treatment times for radiosurgery and mitigating the effects of motion. Recently, even higher doses (e.g., 100 times greater) have become targeted because of their potential to generate the FLASH effect (FE). We refer to these physical dose rates as ultra-high (UHDR). The complete relationship between UHDR and the FE is unknown. But UHDR systems are needed to explore the relationship further and to deliver clinical UHDR treatments, where indicated. Despite the challenging set of unknowns, the authors seek to make reasonable assumptions to probe how existing and developing technology can address the UHDR conditions needed to provide beam generation capable of producing the FE in preclinical and clinical applications. As a preface, this paper discusses the known and unknown relationships between UHDR and the FE. Based on these, different accelerator and ionizing radiation types are then discussed regarding the relevant UHDR needs. The details of UHDR beam production are discussed for existing and potential future systems such as linacs, cyclotrons, synchrotrons, synchrocyclotrons, and laser accelerators. In addition, various UHDR delivery mechanisms are discussed, along with required developments in beam diagnostics and dose control systems.

  • Rotation of the polarization of light as a tool for investigating the collisional transfer of angular momentum from rotating molecules to macroscopic gas flows

    Tutunnikov I., Steinitz U., Gershnabel E., Hartmann J. M., Milner A. A., Milner V. & Averbukh I. S. (2022) Physical Review Research.
    We present a detailed theoretical and experimental study of the rotation of the plane of polarization of light traveling through a gas of fast-spinning molecules. This effect is similar to the polarization drag phenomenon predicted by Fermi a century ago and it is a mechanical analog of the Faraday effect. In our experiments, molecules were spun up by an optical centrifuge and brought to the super-rotor state that retains its rotation for a relatively long time. Polarizability properties of fast-rotating molecules were analyzed considering the rotational Doppler effect and Coriolis forces. We used molecular dynamics simulations to account for intermolecular collisions. We found, both experimentally and theoretically, a nontrivial nonmonotonic time dependence of the polarization rotation angle. This time dependence reflects the transfer of the angular momentum from rotating molecules to the macroscopic gas flow, which may lead to the birth of gas vortices. Moreover, we show that the long-term behavior of the polarization rotation is sensitive to the details of the intermolecular potential. Thus, the polarization drag effect appears as a novel diagnostic tool for the characterization of intermolecular interaction potentials and studies of collisional processes in gases.

  • Photon Correlations in Spectroscopy and Microscopy

    Lubin G., Oron D., Rossman U., Tenne R. & Yallapragada V. J. (2022) ACS Photonics.
    Measurements of photon temporal correlations have been the mainstay of experiments in quantum optics. Over the past several decades, advancements in detector technologies have supported further extending photon correlation techniques to give rise to novel spectroscopy and imaging methods. This Perspective reviews the evolution of these techniques from temporal autocorrelations through multidimensional photon correlations to photon correlation imaging. State-of-the-art single-photon detector technologies are discussed, highlighting the main challenges and the unique current perspective of photon correlations to usher in a new generation of spectroscopy and imaging modalities.

  • Quantum state transfer between a frequency-encoded photonic qubit and a quantum dot spin in a nanophotonic waveguide

    Chan M. L., Aqua Z., Tiranov A., Dayan B., Lodahl P. & Sørensen A. S. (2022) Physical review. A.
    We propose a deterministic yet fully passive scheme to transfer the quantum state from a frequency-encoded photon to the spin of a quantum dot mediated by a nanophotonic waveguide. We assess the quality of the state transfer by studying the effects of all relevant experimental imperfections on the state-transfer fidelity. We show that a transfer fidelity exceeding 95% is achievable for experimentally realistic parameters. Our work sets the stage for deterministic solid-state quantum networks tailored to frequency-encoded photonic qubits.

  • Digitally controlled multimode laser for high-resolution and robust beam shaping

    Mahler S., Tradonsky C., Pal V., Friesem A. A. & Davidson N. (2022) .
    Laser beams can be shaped by controlling either the intensity or phase or coherence distribution separately. With typical laser configurations, the intensity and phase controls are relatively slow and cannot yield high-resolution arbitrarily shaped beams and the coherence control suffers from high power loss. By resorting to a degenerate cavity laser that incorporates an intra-cavity digital spatial light modulator and an intra-cavity spatial Fourier filter, it is possible to exploit a very large number (about 100,000) of independent lasing spatial modes in order to control the properties of the laser output. We have adapted this configuration to develop a novel, rapid and efficient method to generate highresolution laser beams with arbitrary intensity, phase and coherence distributions.

  • Comparing two-qubit and multiqubit gates within the toric code

    Schwerdt D., Shapira Y., Manovitz T. & Ozeri R. (2022) Physical review. A.
    In some quantum computing architectures, entanglement of an arbitrary number of qubits can be generated in a single operation. This property has many potential applications, and may specifically be useful for quantum error correction (QEC). Stabilizer measurements can then be implemented using a single multiqubit gate instead of several two-qubit gates, thus reducing circuit depth. In this study, the toric code is used as a benchmark to compare the performance of two-qubit and five-qubit gates within parity-check circuits. We consider trapped ion qubits that are controlled via Raman transitions, where the primary source of error is assumed to be spontaneous photon scattering. We show that a five-qubit Molmer-Sorensen gate offers an approximately 40% improvement over two-qubit gates in terms of the fault tolerance threshold. This result indicates an advantage of using multiqubit gates in the context of QEC.

  • Anti-Zeno purification of spin baths by quantum probe measurements

    Dasari D. B. R., Yang S., Chakrabarti A., Finkler A., Kurizki G. & Wrachtrup J. (2022) Nature Communications.
    The quantum Zeno and anti-Zeno paradigms have thus far addressed the evolution control of a quantum system coupled to an immutable bath via non-selective measurements performed at appropriate intervals. We fundamentally modify these paradigms by introducing, theoretically and experimentally, the concept of controlling the bath state via selective measurements of the system (a qubit). We show that at intervals corresponding to the anti-Zeno regime of the system-bath exchange, a sequence of measurements has strongly correlated outcomes. These correlations can dramatically enhance the bath-state purity and yield a low-entropy steady state of the bath. The purified bath state persists long after the measurements are completed. Such purification enables the exploitation of spin baths as long-lived quantum memories or as quantum-enhanced sensors. The experiment involved a repeatedly probed defect center dephased by a nuclear spin bath in a diamond at low-temperature. The existing paradigms of system-bath control typically assume that the bath state is unchanged. By using spin defects in diamond, Dasari et al. demonstrate a scheme for controlling the state of the nuclear spin bath via selective measurements of the central qubit as a way of extending the qubit coherence time.

  • Observation of light-driven band structure via multiband high-harmonic spectroscopy

    Uzan-Narovlansky A. J., Jiménez-Galán Á., Orenstein G., Silva R. E. F., Arusi-Parpar T., Shames S., Bruner B. D., Yan B., Smirnova O., Ivanov M. & Dudovich N. (2022) Nature Photonics.
    Intense light–matter interactions have revolutionized our ability to probe and manipulate quantum systems at sub-femtosecond timescales 1 , opening routes to the all-optical control of electronic currents in solids at petahertz rates 2–7 . Such control typically requires electric-field amplitudes in the range of almost volts per angstrom, when the voltage drop across a lattice site becomes comparable to the characteristic bandgap energies. In this regime, intense light–matter interaction induces notable modifications to the electronic and optical properties 8–10 , dramatically modifying the crystal band structure. Yet, identifying and characterizing such modifications remain an outstanding problem. As the oscillating electric field changes within the driving field’s cycle, does the band structure follow and how can it be defined? Here we address this fundamental question, proposing all-optical spectroscopy to probe the laser-induced closing of the bandgap between adjacent conduction bands. Our work reveals the link between nonlinear light–matter interactions in strongly driven crystals and the sub-cycle modifications in their effective band structure.

  • Quantum suppression of cold reactions far from the quantum regime

    Katz O., Pinkas M., Akerman N. & Ozeri R. (2022) arxiv.org.
    Reactions between pairs of atoms are ubiquitous processes in chemistry and physics. Quantum scattering effects on reactions are only observed at extremely ultracold temperatures, close to the s-wave regime, with a small number of partial waves involved. At higher temperatures, the different phases associated with the centrifugal barriers of different partial waves average-out quantum interference to yield semi-classical reaction rates. Here we use quantum-logic to experimentally study resonant charge-exchange reactions between single cold pairs of neutral 87Rb atoms and optically-inaccessible 87Rb+ ions far above the s-wave regime. We find that the measured charge-exchange rate is greatly suppressed with respect to the semi-classical prediction. Our results indicate for the first time that quantum interference persists and effects reaction rates at very high temperatures, at least three orders of magnitude higher than the ultracold s-wave regime.

  • Quantum Zeno and Anti-Zeno Probes of Noise Correlations in Photon Polarization

    Virzì S., Avella A., Piacentini F., Gramegna M., Opatrný T., Kofman A. G., Kurizki G., Gherardini S., Caruso F., Degiovanni I. P. & Genovese M. (2022) Physical review letters.
    We experimentally demonstrate, for the first time, noise diagnostics by repeated quantum measurements, establishing the ability of a single photon subjected to random polarization noise to diagnose non-Markovian temporal correlations of such a noise process. Both the noise spectrum and temporal correlations are diagnosed by probing the photon with frequent (partially) selective polarization measurements. We show that noise with positive temporal correlations corresponds to our single photon undergoing a dynamical regime enabled by the quantum Zeno effect (QZE), whereas noise characterized by negative (anti) correlations corresponds to regimes associated with the anti-Zeno effect (AZE). This is the first step toward a novel noise spectroscopy based on QZE and AZE in single-photon state probing able to extract information on the noise while protecting the probe state, a conceptual paradigm shift with respect to traditional interferometric measurements.

  • Enhanced Photocatalytic and Photoluminescence Properties Resulting from Type-I Band Alignment in the Zn2GeO4/g-C3N4 Nanocomposites

    Suzuki V. Y., Amorin L. H. C., Fabris G. S. L., Dey S., Sambrano J. R., Cohen H., Oron D. & La Porta F. A. (2022) Catalysts.
    Well-defined Zn2GeO4/g-C3N4 nanocomposites with a band alignment of type-I were prepared by the ultrasound-assisted solvent method, starting from g-C3N4 nanosheets and incorporating 0, 10, 20, and 40 wt% of Zn2GeO4. In this study, we have investigated in-depth the photoluminescence emission and photocatalytic activity of these nanocomposites. Our experimental results showed that an increased mass ratio of Zn2GeO4 to g-C3N4 can significantly improve their photoluminescence and photocatalytic responses. Additionally, we have noted that the broadband photoluminescence (PL) emission for these nanocomposites reveals three electronic transitions; the first two well-defined transitions (at ca. 450 nm and 488 nm) can be attributed to π*→ lone pair (LP) and π*→π transitions of g-C3N4, while the single shoulder at ca. 532 nm is due to the oxygen vacancy (Vo) as well as the hybridization of 4s and 4p orbital states in the Zn and Ge belonging to Zn2GeO4. These experimental findings are also supported by theoretical calculations performed under periodic conditions based on the density functional theory (DFT) fragment. The theoretical findings for these nanocomposites suggest a possible strain-induced increase in the Zn-O bond length, as well as a shortening of the Ge-O bond of both tetrahedral [ZnO4] and [GeO4] clusters, respectively. Thus, this disordered structure promotes local polarization and a charge gradient in the Zn2GeO4/g-C3N4 interface that enable an efficient separation and transfer of the photoexcited charges. Finally, theoretical results show a good correlation with our experimental data.

  • Real-time full-field imaging through scattering media by all-optical feedback

    Chriki R., Mahler S., Tradonsky C., Friesem A. A. & Davidson N. (2022) Physical Review A.
    Full-field imaging through scattering media is fraught with many challenges. Despite many achievements, current imaging methods are too slow to deal with fast dynamics, e.g., in biomedical imaging. We present an ultrafast all-optical method where a highly multimode self-imaging laser cavity is built around the reflective object to be imaged and the scattering medium. We show that the intracavity laser light from the object is mainly focused onto specific regions of the scattering medium where the phase variations are low. Thus, round-trip loss within the laser cavity is minimized, thereby overcoming most of the scattering effects. Our method can deal with temporal variations that occur on timescales as short as several cavity round trips, typically 100 ns in our laser cavity.

  • Rotation of Polarization of Light Propagating Through a Gas of Molecular Super-rotors [1]

    Tutunnikov I., Steinitz U., Gershnabel E., Hartmann J. M., Milner A. A., Milner V. & Averbukh I. S. (2022) .
    We present a theoretical-experimental study of polarization rotation of light traveling through a gas of fast-spinning molecules. The long-term behavior of the polarization angle can be used for probing relaxation dynamics in molecular gases.

  • Tapered Optical Fibers Coated with Rare-Earth Complexes for Quantum Applications

    Mor Markovsky O. E., Ohana T., Borne A., Diskin Posner Y., Asher M., Yaffe O., Shanzer A. & Dayan B. (2022) ACS Photonics.
    Crystals and fibers doped with rare-earth (RE) ions provide the basis for most of today’s solid-state optical systems, from lasers and telecom devices to emerging potential quantum applications such as quantum memories and optical to microwave conversion. The two platforms, doped crystals and doped fibers, seem mutually exclusive, each having its own strengths and limitations, the former providing high homogeneity and coherence and the latter offering the advantages of robust optical waveguides. Here we present a hybrid platform that does not rely on doping but rather on coating the waveguide─a tapered silica optical fiber─with a monolayer of complexes, each containing a single RE ion. The complexes offer an identical, tailored environment to each ion, thus minimizing inhomogeneity and allowing tuning of their properties to the desired application. Specifically, we use highly luminescent Yb3+[Zn(II)MC (QXA)] complexes, which isolate the RE ion from the environment and suppress nonradiative decay channels. We demonstrate that the beneficial optical transitions of the Yb3+ are retained after deposition on the tapered fiber and observe an excited-state lifetime of over 0.9 ms, on par with state-of-the-art Yb-doped inorganic crystals.

  • Characterization of spatiotemporal couplings with far-field beamlet cross-correlation

    Smartsev S., Tata S., Liberman A., Adelberg M., Mohanty A., Levine E., Seeman O., Wan Y., Kroupp E., Lahaye R., Thaury C. & Malka V. (2022) Journal of optics (2010).
    We present a novel, straightforward method for the characterization of spatiotemporal couplings in ultra-short laser pulses. The method employs far-field interferometry and inverse Fourier transform spectroscopy, built on the theoretical basis derived in this paper. It stands out in its simplicity: it requires few non-standard optical elements and simple analysis algorithms. This method was used to measure the space-time intensity of our 100 TW class laser and to test the efficacy of a refractive doublet as a suppressor of pulse front curvature (PFC). The measured low-order spatiotemporal couplings agreed with ray-tracing simulations. In addition, we demonstrate a one-shot measurement technique, derived from our central method, which allows for quick and precise alignment of the compressor by pulse front tilt (PFT) minimization and for optimal refractive doublet positioning for the suppression of PFC.

  • Transforming Space with Non-Hermitian Dielectrics

    Krešić I., Makris K. G., Leonhardt U. & Rotter S. (2022) Physical review letters.
    Coordinate transformations are a versatile tool to mold the flow of light, enabling a host of astonishing phenomena such as optical cloaking with metamaterials. Moving away from the usual restriction that links isotropic materials with conformal transformations, we show how nonconformal distortions of optical space are intimately connected to the complex refractive index distribution of an isotropic non-Hermitian medium. Remarkably, this insight can be used to circumvent the material requirement of working with refractive indices below unity, which limits the applications of transformation optics. We apply our approach to design a broadband unidirectional dielectric cloak, which relies on nonconformal coordinate transformations to tailor the non-Hermitian refractive index profile around a cloaked object. Our insights bridge the fields of two-dimensional transformation optics and non-Hermitian photonics.

  • Low divergence proton beams from a laser-plasma accelerator at kHz repetition rate

    Levy D., Andriyash I. A., Haessler S., Kaur J., Ouillé M., Flacco A., Kroupp E., Malka V. & Lopez-Martens R. (2022) Physical Review Accelerators and Beams.
    Proton beams with up to 100 pC bunch charge, 0.48 MeV cutoff energy, and divergence as low as 3° were generated from solid targets at kHz repetition rate by a few-mJ femtosecond laser under controlled plasma conditions. The beam spatial profile was measured using a small aperture scanning time-of-flight detector. Detailed parametric studies were performed by varying the surface plasma scale length from 8 to 80 nm and the laser pulse duration from 4 fs to 1.5 ps. Numerical simulations are in good agreement with observations and, together with an in-depth theoretical analysis of the acceleration mechanism, indicate that high repetition rate femtosecond laser technology could be used to produce few-MeV proton beams for applications.

  • Femtosecond rotational dynamics of D$_2$ molecules in superfluid helium nanodroplets

    Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) arxiv.org.
    Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond (fs) pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed fs probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

  • Self-Healing and Light-Soaking in MAPbI<sub>3</sub>: The Effect of H<sub>2</sub>O

    Ceratti D. R., Tenne R., Bartezzaghi A., Cremonesi L., Segev L., Kalchenko V., Oron D., Potenza M. A. C., Hodes G. & Cahen D. (2022) Advanced Materials.
    The future of halide perovskites (HaPs) is beclouded by limited understanding of their long-term stability. While HaPs can be altered by radiation that induces multiple processes, they can also return to their original state by “self-healing.” Here two-photon (2P) absorption is used to effect light-induced modifications within MAPbI<sub>3</sub> single crystals. Then the changes in the photodamaged region are followed by measuring the photoluminescence, from 2P absorption with 2.5 orders of magnitude lower intensity than that used for photodamaging the MAPbI<sub>3</sub>. After photodamage, two brightening and one darkening process are found, all of which recover but on different timescales. The first two are attributed to trap-filling (the fastest) and to proton-amine-related chemistry (the slowest), while photodamage is attributed to the lead-iodide sublattice. Surprisingly, while after 2P-irradiation of crystals that are stored in dry, inert ambient, photobrightening (or “light-soaking”) occurs, mostly photodarkening is seen after photodamage in humid ambient, showing an important connection between the self-healing of a HaP and the presence of H<sub>2</sub>O, for long-term steady-state illumination, practically no difference remains between samples kept in dry or humid environments. This result suggests that photobrightening requires a chemical-reservoir that is sensitive to the presence of H<sub>2</sub>O, or possibly other proton-related, particularly amine, chemistry.

  • Anomalous optical drag

    Banerjee C., Solomons Y., Black A. N., Marcucci G., Eger D., Davidson N., Firstenberg O. & Boyd R. W. (2022) Physical Review Research.
    A moving dielectric medium can displace the optical path of light passing through it, a phenomenon known as the Fresnel-Fizeau optical drag effect. The resulting displacement is proportional to the medium's velocity. In this paper, we report on the observation of an anomalous optical drag effect, where the displacement is still proportional to the medium's speed but along the direction opposite to the medium's movement. We conduct an optical drag experiment under conditions of electromagnetically induced transparency and observe the transition from normal, to null, to anomalous optical drag by modification of the two-photon detuning.

  • Two-mirror compact system for ideal concentration of diffuse light

    Steinberg S., Bokor N. & Davidson N. (2022) Journal of the Optical Society of America. A, Optics, image science, and vision.
    We introduce a simple, compact two-mirror system for diffuse light concentration. The design principle is based on local conservation of optical brightness. The system design is flexible, and we are able to compute mirror shapes given arbitrary incident beam direction and target cross-sectional shape. As illustration, we showcase our design for flat and cylindrical target geometries, and we also demonstrate that our system is able to concentrate efficiently along one or two dimensions. We perform numeric experiments that confirm our theoretical results and provide diffuse light concentration very close to the thermodynamic limit in all cases we considered.

  • Controlling Nonlinear Interaction in a Many-Mode Laser by Tuning Disorder

    Eliezer Y., Mahler S., Friesem A. A., Cao H. & Davidson N. (2022) Physical review letters.
    A many-mode laser with nonlinear modal interaction could serve as a model system to study many-body physics. However, precise and continuous tuning of the interaction strength over a wide range is challenging. Here, we present a unique method for controlling lasing mode structures by introducing random phase fluctuation to a nearly degenerate cavity. We show numerically and experimentally that as the characteristic scale of phase fluctuation decreases by two orders of magnitude, the transverse modes become fragmented and the reduction of their spatial overlap suppresses modal competition for gain, allowing more modes to lase. The tunability, flexibility, and robustness of our system provides a powerful platform for investigating many-body phenomena.

  • Anyonic-parity-time symmetry in complex-coupled lasers

    Arwas G., Gadasi S., Gershenzon I., Friesem A., Davidson N. & Raz O. (2022) Science advances.
    Non-Hermitian Hamiltonians, and particularly parity-time (PT) and anti-PT symmetric Hamiltonians, play an important role in many branches of physics, from quantum mechanics to optical systems and acoustics. Both the PT and anti-PT symmetries are specific instances of a broader class known as anyonic-PT symmetry, where the Hamiltonian and the PT operator satisfy a generalized commutation relation. Here, we study theoretically these novel symmetries and demonstrate them experimentally in coupled lasers systems. We resort to complex coupling of mixed dispersive and dissipative nature, which allows unprecedented control on the location in parameter space where the symmetry and symmetry breaking occur. Moreover, tuning the coupling in the same physical system allows us to realize the special cases of PT and anti-PT symmetries. In a more general perspective, we present and experimentally validate a new relation between laser synchronization and the symmetry of the underlying non-Hermitian Hamiltonian.

  • Quantum capacity and codes for the bosonic loss-dephasing channel

    Leviant P., Xu Q., Jiang L. & Rosenblum S. (2022) Quantum.
    Bosonic qubits encoded in continuous-variable systems provide a promising alternative to two-level qubits for quantum computation and communication. So far, photon loss has been the dominant source of errors in bosonic qubits, but the significant reduction of photon loss in recent bosonic qubit experiments suggests that dephasing errors should also be considered. However, a detailed understanding of the combined photon loss and dephasing channel is lacking. Here, we show that, unlike its constituent parts, the combined loss-dephasing channel is non-degradable, pointing towards a richer structure of this channel. We provide bounds for the capacity of the loss-dephasing channel and use numerical optimization to find optimal single-mode codes for a wide range of error rates.

  • Long-lasting Orientation induced by Two-Color Femtosecond Laser Pulses

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) .
    We theoretically demonstrate the long-lasting orientation of symmetric- and asymmetric-top molecules induced by a two-color laser pulse.

  • Direct observation of relativistic broken plasma waves

    Wan Y., Seemann O., Tata S., Andriyash I., Smartsev S., Kroupp E. & Malka V. A. (2022) Nature Physics.
    Plasma waves contribute to many fundamental phenomena, including astrophysics1, thermonuclear fusion2 and particle acceleration3. Such waves can develop in numerous ways, from classic Langmuir oscillations carried by electron thermal motion4, to the waves excited by an external force and travelling with a driver5. In plasma-based particle accelerators3,6, a strong laser or relativistic particle beam launches plasma waves with field amplitude that follows the driver strength up to the wavebreaking limit5,7, which is the maximum wave amplitude that a plasma can sustain. In this limit, plasma electrons gain sufficient energy from the wave to outrun it and to get trapped inside the wave bucket8. Theory and numerical simulations predict multi-dimensional wavebreaking, which is crucial in the electron self-injection process that determines the accelerator performances9,10. Here we present a real-time experimental visualization of the laser-driven nonlinear relativistic plasma waves by probing them with a femtosecond high-energy electron bunch from another laser-plasma accelerator coupled to the same laser system. This single-shot electron deflectometry allows us to characterize nonlinear plasma wakefield with femtosecond temporal and micrometre spatial resolutions revealing features of the plasma waves at the breaking point.

  • Characteristics of bright betatron radiation from relativistic self-trapping of a short laser pulse in near-critical density plasma

    Vais O., Lobok M., Andriyash I., Malka V. & Bychenkov V. (2022) .
    We discuss the x-ray generation by electrons ac-celerated in the relativistic self-trapping regime of laser pulse propagation. It is shown that the secondary radiation has a high brightness. At the same time, this regime is accompanied by the particle interaction with a laser pulse that ensures partial polarization of synchrotron radiation and its nonisotropic angular distributions.

  • Optical quantum memory for noble-gas spins based on spin-exchange collisions

    Katz O., Shaham R., Reches E., Gorshkov A. & Firstenberg O. (2022) Physical review. A.
    Optical quantum memories, which store and preserve the quantum state of photons, rely on a coherent mapping of the photonic state onto matter states that are optically accessible. Here we outline and characterize schemes to map the state of photons onto long-lived but optically inaccessible collective states of noble-gas spins. The mapping employs coherent spin-exchange interaction arising from random collisions with alkali vapor. We propose efficient storage strategies in two operating regimes and analyze their performance for several proposed experimental configurations.

  • Optimization of the double-laser-pulse scheme for enantioselective orientation of chiral molecules

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) The Journal of chemical physics.
    We present a comprehensive study of enantioselective orientation of chiral molecules excited by a pair of delayed cross-polarized femtosecond laser pulses. We show that by optimizing the pulses’ parameters, a significant degree (∼10%) of enantioselective orientation can be achieved at 0 and 5 K rotational temperatures. This study suggests a set of reasonable experimental conditions for inducing and measuring strong enantioselective orientation. The strong enantioselective orientation and the wide availability of the femtosecond laser systems required for the proposed experiments may open new avenues for discriminating and separating molecular enantiomers.

  • Using Heralded Spectrometry to Measure the Biexciton Binding Energy of an Individual Quantum Dot

    Tenne R., Lubin G., Ulku A. C., Antolovic I. M., Burri S., Karg S., Yallapragada V. J., Bruschini C., Charbon E. & Oron D. (2022) .
    Spectrometry of a quantum state of light is a fundamental challenge with practical implications. Here, we demonstrate how such a technique can super-resolve the exciton and biexciton energies in a single quantum dot at room temperature.

  • Femtosecond Rotational Dynamics of D2 Molecules in Superfluid Helium Nanodroplets

    Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) Physical review letters.
    Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed femtosecond probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

  • Directing the Morphology, Packing, and Properties of Chiral MetalOrganic Frameworks by Cation Exchange

    Nasi H., Chiara di Gregorio M., Wen Q., Shimon L. J. W., Kaplan-Ashiri I., Bendikov T., Leitus G., Kazes M., Oron D., Lahav M. & van der Boom M. E. (2022) Angewandte Chemie (International ed.).
    We show that metal-organic frameworks, based on tetrahedral pyridyl ligands, can be used as a morphological and structural template to form a series of isostructural crystals having different metal ions and properties. An iterative crystal-to-crystal conversion has been demonstrated by consecutive cation exchanges. The primary manganese-based crystals are characterized by an uncommon space group ( P622 ). The packing includes chiral channels that can mediate the cation exchange, as indicated by energy-dispersive X-ray spectroscopy on microtome-sectioned crystals. The observed cation exchange is in excellent agreement with the Irving-Williams series (Mn < Fe < Co < Ni < Cu > Zn) associated with the relative stability of the resulting coordination nodes. Furthermore, we demonstrate how the metal cation controls the optical and magnetic properties. The crystals maintain their morphology, allowing a quantitative comparison of their properties at both the ensemble and single-crystal level.

  • Ternary host-guest complexes with rapid exchange kinetics and photoswitchable fluorescence

    Gemen J., Białek M. J., Kazes M., Shimon L. J. W., Feller M., Semenov S. N., Diskin-Posner Y., Oron D. & Klajn R. (2022) Chem.
    Confinement within molecular cages can dramatically modify the physicochemical properties of the encapsulated guest molecules, but such host-guest complexes have mainly been studied in a static context. Combining confinement effects with fast guest exchange kinetics could pave the way toward stimuli-responsive supramolecular systems—and ultimately materials—whose desired properties could be tailored “on demand” rapidly and reversibly. Here, we demonstrate rapid guest exchange between inclusion complexes of an open-window coordination cage that can simultaneously accommodate two guest molecules. Working with two types of guests, anthracene derivatives and BODIPY dyes, we show that the former can substantially modify the optical properties of the latter upon noncovalent heterodimer formation. We also studied the light-induced covalent dimerization of encapsulated anthracenes and found large effects of confinement on reaction rates. By coupling the photodimerization with the rapid guest exchange, we developed a new way to modulate fluorescence using external irradiation.

  • Halide chemical vapor deposition of 2D semiconducting atomically-thin crystals: From self-seeded to epitaxial growth

    Patsha A., Ranganathan K., Kazes M., Oron D. & Ismach A. (2022) Applied Materials Today.
    Atomically-thin crystals remain an epicenter of today's ongoing efforts of materials exploration for both fundamental knowledge and technological applications. We show that key modifications in the nucleation and growth steps lead to a controlled self-seeded growth of the monolayer transition metal dichalcogenide (TMDC) crystals and their lateral heterostructures via an halide chemical vapor deposition (HCVD) process which is a proven industrial scale and carbon-free synthesis technique for various material types. We present a general growth model with the limiting conditions on the nucleation density and crystal size of the 2D TMDCs grown in HCVD process. Furthermore, upon reduction of the self-seeded growth by a suitable surface pre-treatment, and by the modification of the nucleation step, epitaxial growth of monolayer TMDCs is also demonstrated using HCVD approach. The steady-state and time-resolved photoluminescence spectroscopic studies revealed the high optical and electronic quality of the as-grown 2D TMDCs semiconducting crystals. Field-effect transistor device characteristics of HCVD grown monolayer MoS2 using SiO2 gate dielectric shows an average mobility of 26 ± 7 cm2.V−1.s−1 and on-off ratio of ∼107, promising for large-scale device applications.

  • Strong coupling of alkali-metal spins to noble-gas spins with an hour-long coherence time

    Shaham R., Katz O. & Firstenberg O. (2022) Nature Physics.
    Nuclear spins of noble gases can maintain coherence for hours at ambient conditions because they are isolated by complete electron shells(1). This isolation, however, impedes the ability to manipulate and control them by optical means or by coupling to other spin gases(2-4). Here we achieve strong coherent coupling between noble-gas spins and the optically accessible spins of an alkali-metal vapour. The coupling emerges from the coherent accumulation of stochastic spin-exchange collisions. We obtain a coupling strength ten times higher than the decay rate, observe the coherent and periodic exchange of spin excitations between the two gases and demonstrate active control over the coupling by an external magnetic field. This approach could be developed into a fast and efficient interface for noble-gas spins, enabling applications in quantum sensing and information(5,6).

  • Trapped-Ion Quantum Computer with Robust Entangling Gates and Quantum Coherent Feedback

    Manovitz T., Shapira Y., Gazit L., Akerman N. & Ozeri R. (2022) PRX Quantum.
    Quantum computers are expected to achieve a significant speed-up over classical computers in solving a range of computational problems. Chains of ions held in a linear Paul trap are a promising platform for constructing such quantum computers, due to their long coherence times and high quality of control. Here, we report on the construction of a small five-qubit universal quantum computer using ^{88}Sr^{+} ions in a radio-frequency (rf) trap. All basic operations, including initialization, quantum logic operations, and readout, are performed with high fidelity. Selective two-qubit and single-qubit gates, implemented using a narrow-line-width laser, comprise a universal gate set, allowing realization of any unitary on the quantum register. We review the main experimental tools and describe in detail unique aspects of the computer: the use of robust entangling gates and the development of a quantum coherent feedback system through electron-multiplying CCD camera acquisition. The latter is necessary for carrying out quantum error-correction protocols in future experiments.

  • Commissioning and first results from the new 2 × 100 TW laser at the WIS

    Kroupp E., Tata S., Wan Y., Levy D., Smartsev S., Levine E. Y., Seemann O., Adelberg M., Piliposian R., Queller T., Segre E., Ta Phuoc K., Kozlova M. & Malka V. (2022) Matter and Radiation at Extremes.
    At the Weizmann Institute of Science, a new high-power-laser laboratory has been established that is dedicated to the fundamental aspects of laser–matter interaction in the relativistic regime and aimed at developing compact laser-plasma accelerators for delivering high-brightness beams of electrons, ions, and x rays. The HIGGINS laser system delivers two independent 100 TW beams and an additional probe beam, and this paper describes its commissioning and presents the very first results for particle and radiation beam delivery.

  • Non-conformal cloaking with non-Hermitian dielectrics

    Krešić I., Makris K. G., Leonhardt U. & Rotter S. (2022) .
    We show how the non-conformal distortions of optical space are connected to the refractive index distributions of isotropic dielectric non-Hermitian media. Using this insight, we design and numerically demonstrate the operation of a broadband unidirectional invisibility cloak. Remarkably, the presence of gain and loss lifts the usual requirement of near zero refractive index values for such cloaks. Our framework provides an unexpected bridge between the fields of transformation optics in isotropic media and non-Hermitian photonics.

  • Complex-Light Lasers

    Davidson N., Mahler S., Friesem A. & Forbes A. (2022) Optics and Photonics News.
    Tailoring modal competition inside lasers is enabling novel sources of complex light—and new approaches to light-based computation.

  • Super-extended nanofiber-guided field for coherent interaction with hot atoms

    Finkelstein R., Winer G., Koplovich D. Z., Arenfrid O., Hoinkes T., Guendelman G., Netser M., Poem E., Rauschenbeutel A., Dayan B. & Firstenberg O. (2021) Optica.
    We fabricate an extremely thin optical fiber that supports a super-extended mode with a diameter as large as 13 times the optical wavelength, residing almost entirely outside the fiber and guided over thousands of wavelengths (5 mm), in order to couple guided light to warm atomic vapor. This unique configuration balances between strong confinement, as evident by saturation powers as low as tens of nW, and long interaction times with the thermal atoms, thereby enabling fast and coherent interactions. We demonstrate narrow coherent resonances (tens of MHz) of electromagnetically induced transparency for signals at the single-photon level and long relaxation times (10 ns) of atoms excited by the guided mode. The dimensions of the guided mode's evanescent field are compatible with the Rydberg blockade mechanism, making this platform particularly suitable for observing quantum non-linear optics phenomena.

  • Anyonic Parity-Time Symmetric Laser

    Arwas G., Gadasi S., Gershenzon I., Friesem A., Davidson N. & Raz O. (2021) .
    Non-Hermitian Hamiltonians play an important role in many branches of physics, from quantum mechanics to acoustics. In particular, the realization of PT, and more recently -- anti-PT symmetries in optical systems has proved to be of great value from both the fundamental as well as the practical perspectives. Here, we study theoretically and demonstrate experimentally a novel anyonic-PT symmetry in a coupled lasers system. This is achieved using complex coupling -- of mixed dispersive and dissipative nature, which allows unprecedented control on the location in parameter space where the symmetry and symmetry-breaking occur. Moreover, our method allows us to realize the more familiar special cases of PT and anti-PT symmetries using the same physical system. In a more general perspective, we present and experimentally validate a new relation between laser synchronization and the symmetry of the underlying non-Hermitian Hamiltonian.

  • Rapid fair sampling of the XY spin Hamiltonian with a laser simulator

    Pal V., Mahler S., Tradonsky C., Friesem A. A. & Davidson N. (2021) Physical Review Research.
    Coupled oscillators such as lasers, optical parametric oscillators, and Bose-Einstein-condensate polaritons can rapidly and efficiently dissipate into a stable phase-locked state that can be mapped onto the minimal energy (ground state) of classical spin Hamiltonians. However, for degenerate or near-degenerate ground-state manifolds, statistical fair sampling is required to obtain complete knowledge of the minimal-energy state, which needs many repetitions of simulations under identical conditions. We show that with dissipatively coupled lasers such fair sampling can be achieved rapidly and accurately by exploiting the many longitudinal modes of each laser to form an ensemble of identical but independent simulators, acting in parallel. We fairly sampled the ground-state manifold of square, triangular, and kagome lattices by measuring their coherence function and identifying manifolds composed of single, doubly degenerate, and highly degenerate ground states, respectively.

  • Bright Near-Infrared to Visible Upconversion Double Quantum Dots Based on a Type-II/Type-I Heterostructure

    Yang G., Kazes M., Raanan D. & Oron D. (2021) ACS Photonics.
    Upconverting semiconductor quantum dots (QDs) combine the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. Here, we present upconverting type-II/type-I colloidal double QDs that enable enhancement of the performance of near-infrared to visible photon upconversion in QDs and broadening the range of relevant materials used. The resulting ZnTe/CdSe@CdS@CdSe/ZnSe type-II/type-I double QDs possess a very high photoluminescence quantum yield, monoexponential decay dynamics, and a narrow line width, approaching those of state-of-the-art upconverting QDs. We quantitatively characterize the upconversion cross section by direct comparison with two-photon absorption when varying the pump frequency across the absorption edge. Finally, we show that these upconversion QDs maintain their optical performance in a much more demanding geometry of a dense solid film and can thus be incorporated in devices as upconversion films. Our design provides guidance for fabricating highly efficient upconverting QDs with potential applications such as security coding and bioimaging.

  • Critical dynamics and phase transition of a strongly interacting warm spin gas

    Horowicz Y., Katz O., Raz O. & Firstenberg O. (2021) Proceedings of the National Academy of Sciences - PNAS.
    Phase transitions are emergent phenomena where microscopic interactions drive a disordered system into a collectively ordered phase. Near the boundary between two phases, the system can exhibit critical, scale-invariant behavior. Here, we report on a second-order phase transition accompanied by critical behavior in a system of warm cesium spins driven by linearly-polarized light. The ordered phase exhibits macroscopic magnetization when the interactions between the spins become dominant. We measure the phase diagram of the system and observe the collective behavior near the phase boundaries, including power-law dependence of the magnetization and divergence of the susceptibility. Out of equilibrium, we observe a critical slow-down of the spin response time by two orders of magnitude, exceeding five seconds near the phase boundary. This work establishes a controlled platform for investigating equilibrium and nonequilibrium properties of magnetic phases.

  • Heralded Spectroscopy Reveals Exciton–Exciton Correlations in Single Colloidal Quantum Dots

    Lubin G., Tenne R., Ulku A. C., Antolovic I. M., Burri S., Karg S., Yallapragada V. J., Bruschini C., Charbon E. & Oron D. (2021) Nano Letters.
    Multiply excited states in semiconductor quantum dots feature intriguing physics and play a crucial role in nanocrystal-based technologies. While photoluminescence provides a natural probe to investigate these states, room-temperature single-particle spectroscopy of their emission has proved elusive due to the temporal and spectral overlap with emission from the singly excited and charged states. Here, we introduce biexciton heralded spectroscopy enabled by a single-photon avalanche diode array based spectrometer. This allows us to directly observe biexciton–exciton emission cascades and measure the biexciton binding energy of single quantum dots at room temperature, even though it is well below the scale of thermal broadening and spectral diffusion. Furthermore, we uncover correlations hitherto masked in ensembles of the biexciton binding energy with both charge-carrier confinement and fluctuations of the local electrostatic potential. Heralded spectroscopy has the potential of greatly extending our understanding of charge-carrier dynamics in multielectron systems and of parallelization of quantum optics protocols.

  • Bright synchrotron radiation from relativistic self-trapping of a short laser pulse in near-critical density plasma

    Lobok M., Andriyash I., Vais O., Malka V. & Bychenkov V. Y. (2021) Physical Review. E.
    In a dense gas plasma a short laser pulse propagates in a relativistic self-trapping mode, which enables the effective conversion of laser energy to the accelerated electrons. This regime sustains effective loading which maximizes the total charge of the accelerating electrons, that provides a large amount of betatron radiation. The three-dimensional particle-in-cell simulations demonstrate how such a regime triggers x-ray generation with 0.1–1 MeV photon energies, low divergence, and high brightness. It is shown that a 135-TW laser can be used to produce 3 × 1010 photons of >10 keV energy and a 1.2-PW laser makes it possible generating about 1012 photons in the same energy range. The laser-to-gamma energy conversion efficiency is up to 10−4 for the high-energy photons, ∼100 keV, while the conversion efficiency to the entire keV-range x rays is estimated to be a few tenths of a percent.

  • Visualizing coherent molecular rotation in a gaseous medium

    Tutunnikov I., Prost E., Steinitz U., Bejot P., Hertz E., Billard F., Faucher O. & Averbukh I. S. (2021) Physical review. A.
    Inducing and controlling the ultrafast molecular rotational dynamics using shaped laser fields is essential in numerous applications. Several approaches exist that allow following the coherent molecular motion in real time, including Coulomb explosion-based techniques and recovering molecular orientation from the angular distribution of high harmonics. We theoretically consider a nonintrusive optical scheme for visualizing the rotational dynamics in an anisotropic molecular gas. The proposed method allows determining the instantaneous orientation of the principal optical axes of the gas. The method is based on probing the sample using ultrashort circularly polarized laser pulses and recording the transmission image through a vortex wave plate. We consider two example excitations: molecular alignment induced by an intense linearly polarized laser pulse and unidirectional molecular rotation induced by a polarization-shaped pulse. The proposed optical method is promising for visualizing the dynamics of complex symmetric- and asymmetric-top molecules.

  • Resolving the controversy in biexciton binding energy of cesium lead halide perovskite nanocrystals through heralded single-particle spectroscopy

    Lubin G., Yaniv G., Kazes M., Ulku A. C., Antolovic I. M., Burri S., Bruschini C., Charbon E., Yallapragada V. J. & Oron D. (2021) ACS Nano.
    Understanding exciton-exciton interaction in multiply-excited nanocrystals is crucial to their utilization as functional materials. Yet, for lead halide perovskite nanocrystals, which are promising candidates for nanocrystal-based technologies, numerous contradicting values have been reported for the strength and sign of their exciton-exciton interaction. In this work we unambiguously determine the biexciton binding energy in single cesium lead halide perovskite nanocrystals at room temperature. This is enabled by the recently introduced SPAD array spectrometer, capable of temporally isolating biexciton-exciton emission cascades while retaining spectral resolution. We demonstrate that CsPbBr$_3$ nanocrystals feature an attractive exciton-exciton interaction, with a mean biexciton binding energy of 10 meV. For CsPbI$_3$ nanocrystals we observe a mean biexciton binding energy that is close to zero, and individual nanocrystals show either weakly attractive or weakly repulsive exciton-exciton interaction. We further show that within ensembles of both materials, single-nanocrystal biexciton binding energies are correlated with the degree of charge-carrier confinement.

  • A three-step model of high harmonic generation using complex classical trajectories

    Koch W. & Tannor D. J. (2021) Annals of Physics.
    We present a new trajectory formulation of high harmonic generation that treats classically allowed and classically forbidden processes within a single dynamical framework. Complex trajectories orbit the nucleus, producing the stationary Coulomb ground state. When the field is turned on, these complex trajectories continue their motion in the field-dressed Coulomb potential and therefore tunnel ionization, unbound evolution and recollision are described within a single, seamless framework. The new formulation can bring mechanistic understanding to a broad range of strong field physics effects.

  • Long-Lasting Orientation of Symmetric-top Molecules Excited by Two-Color Femtosecond Pulses

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2021) Frontiers in Physics.
    Impulsive orientation of symmetric-top molecules excited by two-color femtosecond pulses is considered. In addition to the well-known transient orientation appearing immediately after the pulse and then reemerging periodically due to quantum revivals, we report the phenomenon of field-free long-lasting orientation. Long-lasting means that the time averaged orientation remains non-zero until destroyed by other physical effects, e.g., intermolecular collisions. The effect is caused by the combined action of the field-polarizability and field-hyperpolarizability interactions. The dependence of degree of long-lasting orientation on temperature and pulse parameters is considered. The effect can be measured by means of second (or higher-order) harmonic generation, and may be used to control the deflection of molecules traveling through inhomogeneous electrostatic fields.

  • Effect of Surface Ligands in Perovskite Nanocrystals: Extending in and Reaching out

    Kazes M., Udayabhaskararao T., Dey S. & Oron D. (2021) Accounts of Chemical Research.
    The rediscovery of the halide perovskite class of compounds and, in particular, the organic and inorganic lead halide perovskite (LHP) materials and lead-free derivatives has reached remarkable landmarks in numerous applications. First among these is the field of photovoltaics, which is at the core of today’s environmental sustainability efforts. Indeed, these efforts have born fruit, reaching to date a remarkable power conversion efficiency of 25.2% for a double-cation Cs, FA lead halide thin film device. Other applications include light and particle detectors as well as lighting. However, chemical and thermal degradation issues prevent perovskite-based devices and particularly photovoltaic modules from reaching the market. The soft ionic nature of LHPs makes these materials susceptible to delicate changes in the chemical environment. Therefore, control over their interface properties plays a critical role in maintaining their stability. Here we focus on LHP nanocrystals, where surface termination by ligands determines not only the stability of the material but also the crystallographic phase and crystal habit. A surface analysis of nanocrystal interfaces revealed the involvement of Brønsted type acid–base equilibrium in the modification of the ligand moieties present, which in turn can invoke dissolution and recrystallization into the more favorable phase in terms of minimization of the surface energy. A large library of surface ligands has already been developed showing both good chemical stability and good electronic surface passivation, resulting in near-unity emission quantum yields for some materials, particularly CsPbBr3. However, most of those ligands have a large organic tail hampering charge carrier transport and extraction in nanocrystal-based solid films.

  • SI-traceable frequency dissemination at 1572.06 nm in a stabilized fiber network with ring topology

    Husmann D., Bernier L., Bertrand M., Calonico D., Chaloulos K., Clausen G., Clivati C., Faist J., Heiri E., Hollenstein U., Johnson A., Mauchle F., Meir Z., Merkt F., Mura A., Scalari G., Scheidegger S., Schmutz H., Sinhal M., Willitsch S. & Morel J. (2021) Optics Express.
    Frequency dissemination in phase-stabilized optical fiber networks for metrological frequency comparisons and precision measurements are promising candidates to overcome the limitations imposed by satellite techniques. However, in an architecture shared with telecommunication data traffic, network constraints restrict the availability of dedicated channels in the commonly-used C-band. Here, we demonstrate the dissemination of an SI-traceable ultrastable optical frequency in the L-band over a 456 km fiber network with ring topology, in which data traffic occupies the full C-band. We characterize the optical phase noise and evaluate a link instability of 4.7 × 10-16 at 1 s and 3.8 × 10-19 at 2000 s integration time, and a link accuracy of 2 × 10-18. We demonstrate the application of the disseminated frequency by establishing the SI-traceability of a laser in a remote laboratory. Finally, we show that our metrological frequency does not interfere with data traffic in the telecommunication channels. Our approach combines an unconventional spectral choice in the telecommunication L-band with established frequency-stabilization techniques, providing a novel, cost-effective solution for ultrastable frequency-comparison and dissemination, and may contribute to a foundation of a world-wide metrological network.

  • Coupling light to a nuclear spin gas with a two-photon linewidth of five millihertz

    Katz O., Shaham R. & Firstenberg O. (2021) Science advances.
    Nuclear spins of noble gases feature extremely long coherence times but are inaccessible to optical photons. Here, we realize a coherent interface between light and noble-gas spins that is mediated by alkali atoms. We demonstrate the optical excitation of the noble-gas spins and observe the coherent back action on the light in the form of high-contrast two-photon spectra. We report on a record two-photon linewidth of 5 ± 0.7 mHz above room temperature, corresponding to a 1-min coherence time. This experiment provides a demonstration of coherent bidirectional coupling between light and noble-gas spins, rendering their long-lived spin coherence accessible for manipulations in the optical domain.

  • Impulsively Excited Gravitational Quantum States: Echoes and Time-resolved Spectroscopy

    Tutunnikov I., Rajitha K., Voronin A. Y., Nesvizhevsky V. & Averbukh I. (2021) Phys.Rev.Lett.
    We theoretically study an impulsively excited quantum bouncer (QB)—a particle bouncing off a surface in the presence of gravity. A pair of time-delayed pulsed excitations is shown to induce a wave-packet echo effect—a partial rephasing of the QB wave function appearing at twice the delay between pulses. In addition, an appropriately chosen observable [here, the population of the ground gravitational quantum state (GQS)] recorded as a function of the delay is shown to contain the transition frequencies between the GQSs, their populations, and partial phase information about the wave-packet quantum amplitudes. The wave-packet echo effect is a promising candidate method for precision studies of GQSs of ultracold neutrons, atoms, and antiatoms confined in closed gravitational traps.

  • Polarity-dependent nonlinear optics of nanowires under electric field

    Ben-Zvi R., Bar-Elli O., Oron D. & Joselevich E. (2021) Nature Communications.
    Polar materials display a series of interesting and widely exploited properties owing to the inherent coupling between their fixed electric dipole and any action that involves a change in their charge distribution. Among these properties are piezoelectricity, ferroelectricity, pyroelectricity, and the bulk photovoltaic effect. Here we report the observation of a related property in this series, where an external electric field applied parallel or anti-parallel to the polar axis of a crystal leads to an increase or decrease in its second-order nonlinear optical response, respectively. This property of electric-field-modulated second-harmonic generation (EFM-SHG) is observed here in nanowires of the polar crystal ZnO, and is exploited as an analytical tool to directly determine by optical means the absolute direction of their polarity, which in turn provides important information about their epitaxy and growth mechanism. EFM-SHG may be observed in any type of polar nanostructures and used to map the absolute polarity of materials at the nanoscale.

  • Revealing the Influence of Molecular Chirality on Tunnel-Ionization Dynamics

    Bloch E., Larroque S., Rozen S., Beaulieu S., Comby A., Beauvarlet S., Descamps D., Fabre B., Petit S., Taieb R., Uzan A. J., Blanchet V., Dudovich N., Pons B. & Mairesse Y. (2021) Physical review. X.
    Light-matter interaction based on strong laser fields enables probing the structure and dynamics of atomic and molecular systems with unprecedented resolutions, through high-order harmonic spectroscopy, laser-induced electron diffraction, and holography. All strong-field processes rely on a primary ionization mechanism where electrons tunnel through the target potential barrier lowered by the laser field. Tunnel ionization is, thus, of paramount importance in strong-field physics and attoscience. However, the tunneling dynamics and properties of the outgoing electronic wave packets often remain hidden beneath the influence of the subsequent scattering of the released electron onto the ionic potential. Here, we present a joint experimental-theoretical endeavor to characterize the influence of sub-barrier dynamics on the amplitude and phase of the wave packets emerging from the tunnel. We use chiral molecules, whose photoionization by circularly polarized light produces forward-backward asymmetric electron distributions with respect to the light propagation direction. These asymmetric patterns provide a background-free signature of the chiral potential in the ionization process. We first implement the attoclock technique, using bicircular two-color fields. We find that, in the tunnel-ionization process, molecular chirality induces a strong forward-backward asymmetry in the electron yield, while the subsequent scattering of the freed electron onto the chiral potential leads to an asymmetric angular streaking of the electron momentum distribution. In order to access the phase of the tunneling wave packets, we introduce subcycle gated chiral interferometry. We employ an orthogonally polarized two-color laser field whose optical chirality is manipulated on a sub-laser-cycle timescale. Numerical simulations are used to interpret the electron interference patterns inherent to this interaction scheme. They show that the combined action of the chiral potential and rotating laser field not only imprints asymmetric ionization amplitudes during the tunneling process, but also induces a forward-backward asymmetric phase profile onto the outgoing electron wave packets. Chiral light-matter interaction thus induces subtle angular-dependent shaping of both the amplitude and the phase of tunneling wave packets.

  • Multi-channel waveguide QED with atomic arrays in free space

    Solomons Y. & Shahmoon E. (2021) arXiv.org.
    We study light scattering off a two-dimensional (2D) array of atoms driven to Rydberg levels. We show that the problem can be mapped to a generalized model of waveguide QED, consisting of multiple 1D photonic channels (transverse modes), each of which directionally coupled to a corresponding Rydberg surface mode of the array. In the Rydberg blockade regime, collective excitations of different surface modes block each other, leading to multi-channel correlated photonic states. Using an analytical approach, we characterize inter-channel quantum correlations, and elucidate the role of collective two-photon resonances of the array. Our results open new possibilities for multimode many-body physics and quantum information with photons in a free-space platform.

  • Single-spin resonance in a van der Waals embedded paramagnetic defect

    Chejanovsky N., Mukherjee A., Geng J., Chen Y., Kim Y., Denisenko A., Finkler A., Taniguchi T., Watanabe K., Dasari D. B. R., Auburger P., Gali A., Smet J. H. & Wrachtrup J. (2021) Nature Materials.
    A plethora of single-photon emitters have been identified in the atomic layers of two-dimensional van der Waals materials1,2,3,4,5,6,7,8. Here, we report on a set of isolated optical emitters embedded in hexagonal boron nitride that exhibit optically detected magnetic resonance. The defect spins show an isotropic ge-factor of ~2 and zero-field splitting below 10 MHz. The photokinetics of one type of defect is compatible with ground-state electron-spin paramagnetism. The narrow and inhomogeneously broadened magnetic resonance spectrum differs significantly from the known spectra of in-plane defects. We determined a hyperfine coupling of ~10 MHz. Its angular dependence indicates an unpaired, out-of-plane delocalized π-orbital electron, probably originating from substitutional impurity atoms. We extracted spin–lattice relaxation times T1 of 13–17 μs with estimated spin coherence times T2 of less than 1 μs. Our results provide further insight into the structure, composition and dynamics of single optically active spin defects in hexagonal boron nitride.

  • Duality of the Principle of Least Action: A New Formulation of Classical Mechanics

    Tannor D. J. (2021) arxiv.org.
    A dual formalism for Lagrange multipliers is developed. The formalism is used to minimize an action function $S(q_2,q_1,T)$ without any dynamical input other than that $S$ is convex. All the key equations of analytical mechanics -- the Hamilton-Jacobi equation, the generating functions for canonical transformations, Hamilton's equations of motion and $S$ as the time integral of the Lagrangian -- emerge as simple consequences. It appears that to a large extent, analytical mechanics is simply a footnote to the most basic problem in the calculus of variations: that the shortest distance between two points is a straight line.

  • Van der Waals anomaly: Analog of dark energy with ultracold atoms

    Efrat I. Y. & Leonhardt U. (2021) Physical review. B.
    In inhomogeneous dielectric media the divergence of the electromagnetic stress is related to the gradients of ɛ and μ, which is a consequence of Maxwell's equations. Investigating spherically symmetric media we show that this seemingly universal relationship is violated for electromagnetic vacuum forces such as the generalized van der Waals and Casimir forces. The stress needs to acquire an additional anomalous pressure. The anomaly is a result of renormalization, the need to subtract infinities in the stress for getting a finite, physical force. The anomalous pressure appears in the stress in media like dark energy appears in the energy-momentum tensor in general relativity. We propose and analyze an experiment to probe the van der Waals anomaly with ultracold atoms. The experiment may not only test an unusual phenomenon of quantum forces but also an analog of dark energy, shedding light where nothing is known empirically.

  • Fast laser speckle suppression with an intracavity diffuser

    Mahler S., Eliezer Y., Yllmaz H., Friesem A. A., Davidson N. & Cao H. (2021) Nanophotonics.
    Fast speckle suppression is crucial for time-resolved full-field imaging with laser illumination. Here, we introduce a method to accelerate the spatial decoherence of laser emission, achieving speckle suppression in the nanosecond integration time scale. The method relies on the insertion of an intracavity phase diffuser into a degenerate cavity laser to break the frequency degeneracy of transverse modes and broaden the lasing spectrum. The ultrafast decoherence of laser emission results in the reduction of speckle contrast to 3% in less than 1 ns.

  • Constraining Rapidly Oscillating Scalar Dark Matter Using Dynamic Decoupling

    Aharony S., Akerman N., Ozeri R., Perez G., Savoray I. & Shaniv R. (2021) Physical review. D.
    We propose and experimentally demonstrate a method for detection of a light scalar dark matter (DM) field through probing temporal oscillations of fundamental constants in an atomic optical transition. Utilizing the quantum information notion of dynamic decoupling (DD) in a tabletop setting, we are able to obtain model-independent bounds on variations of α and me at frequencies up to the MHz scale. We interpret our results to constrain the parameter space of light scalar DM field models. We consider the generic case, where the couplings of the DM field to the photon and the electron are independent, as well as the case of a relaxion DM model, including the scenario of a DM boson star centered around Earth. Given the particular nature of DD, allowing one to directly observe the oscillatory behavior of coherent DM and considering future experimental improvements, we conclude that our proposed method could be complimentary to, and possibly competitive with, gravitational probes of light scalar DM.

  • Measuring the optical properties of nanoscale biogenic spherulites

    Beck L. M., Yallapragada V. J., Upcher A., Palmer B. A., Addadi L. & Oron D. (2021) Optics Express.
    Recent studies of optical reflectors as part of the vision apparatus in the eyes of decapod crustaceans revealed assemblies of nanoscale spherulites - spherical core-shell nanoparticles with radial birefringence. Simulations performed on the system highlighted the advantages of optical anisotropy in enhancing the functionality of these structures. So far, calculations of the nanoparticle optical properties have relied on refractive indices obtained using ab-initio calculations. Here we describe a direct measurement of the tangential refractive index of the spherulites, which corresponds to the in-plane refractive index of crystalline isoxanthopterin nanoplatelets. We utilize measurements of scattering spectra of individual spherulites and determine the refractive index by analyzing the spectral signatures of scattering resonances. Our measurements yield a median tangential refractive index of 1.88, which is in reasonable agreement with theoretical predictions. Furthermore, our results indicate that the optical properties of small spherulite assemblies are largely determined by the tangential index.

  • Three dimensional orientation of small polyatomic molecules excited by two-color femtosecond pulses

    Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2021) Journal of physics. B, Atomic, molecular, and optical physics.
    We study the excitation of asymmetric-top (including chiral) molecules by two-color femtosecond laser pulses. In the cases of non-chiral asymmetric-top molecules excited by an orthogonally polarized two-color pulse, we demonstrate, classically and quantum mechanically, three-dimensional orientation. For chiral molecules, we show that the orientation induced by a cross-polarized two-color pulse is enantioselective along the laser propagation direction, namely, the two enantiomers are oriented in opposite directions. The classical and quantum simulations are in excellent agreement on the short time scale, whereas on the longer time scale, the enantioselective orientation exhibits quantum beats. These observations are qualitatively explained by analyzing the interaction potential between the two-color pulse and molecular (hyper-)polarizability. The prospects for using the enantioselective orientation for enantiomers' separation is discussed.

  • Enantioselective orientation of chiral molecules induced by terahertz pulses with twisted polarization

    Tutunnikov I., Xu L., Field R. W., Nelson K. A., Prior Y. & Averbukh I. S. (2021) Physical Review Research.
    Chirality and chiral molecules are key elements in modern chemical and biochemical industries. Individual addressing, and the eventual separation of chiral enantiomers has been and still is an important elusive task in molecular physics and chemistry, and a variety of methods has been introduced over the years to achieve this goal. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces an enantioselective orientation of these molecules. This orientation persists for a long time, exceeding the duration of the THz pulses by several orders of magnitude, and its dependency on temperature and pulses' parameters is investigated. The persistent orientation may enhance the deflection of the molecules in inhomogeneous electromagnetic fields, potentially leading to viable separation techniques.

  • Enhanced chiral-sensitivity of Coulomb-focused electrons in strong field ionization

    Rozen S., Larroque S., Dudovich N., Mairesse Y. & Pons B. (2021) Journal of physics. B, Atomic, molecular, and optical physics.
    Strong-field light-matter interactions initiate a wide range of phenomena in which the quantum paths of electronic wavepackets can be manipulated by tailoring the laser field. Among the electrons released by a strong laser pulse from atomic and molecular targets, some are subsequently driven back to the vicinity of the ionic core by the oscillating laser field. The trajectories of these returning electrons are bent toward the core by the ionic potential, an effect known as Coulomb focusing. This process, studied over the past two decades, has been associated with the long range influence of the Coulomb potential. Here we explore the structural properties of the Coulomb focusing phenomenon. Specifically, we numerically study the sensitivity of the returning electron dynamics to the anisotropy of the ionic potential. We employ orthogonally polarized two-color strong fields and chiral molecules, whose asymmetric features lead to unambiguous fingerprints of the potential on the freed electrons. The Coulomb-focused electrons show an enhanced sensitivity to chirality, related to an asymmetric attoclock-like angular streaking stemming from field-assisted scattering of the electrons onto the chiral ionic potential. Anisotropic features of the ionic potential thus monitor the motion of Coulomb-focused electrons throughout their returning paths, shedding light on the structural properties of the interaction.

  • Remanent Polarization and Strong Photoluminescence Modulation by an External Electric Field in Epitaxial CsPbBr<sub>3</sub>Nanowires

    Sanders E., Soffer Y., Salzillo T., Rosenberg M., Bar-Elli O., Yaffe O., Joselevich E. & Oron D. (2021) ACS Nano.
    Metal halide perovskites (MHPs) have unique characteristics and hold great potential for next-generation optoelectronic technologies. Recently, the importance of lattice strain in MHPs has been gaining recognition as a significant optimization parameter for device performance. While the effect of strain on the fundamental properties of MHPs has been at the center of interest, its combined effect with an external electric field has been largely overlooked. Here we perform an electric-field-dependent photoluminescence study on heteroepitaxially strained surface-guided CsPbBr<sub>3</sub> nanowires. We reveal an unexpected strong linear dependence of the photoluminescence intensity on the alternating field amplitude, stemming from an induced internal dipole. Using low-frequency polarized-Raman spectroscopy, we reveal structural modifications in the nanowires under an external field, associated with the observed polarity. These results reflect the important interplay between strain and an external field in MHPs and offer opportunities for the design of MHP-based optoelectronic nanodevices.

  • High-resolution digital spatial control of a highly multimode laser

    Tradonsky C., Mahler S., Cai G., Pal V., Chriki R., Friesem A. A. & Davidson N. (2021) Optica.
    We developed a rapid and efficient method for generating laser outputs with arbitrary shaped distributions and properties that are needed for a variety of applications. It is based on simultaneously controlling the intensity, phase, and coherence distributions of the laser. The method involves a digital degenerate cavity laser in which a phase-only spatial light modulator and spatial filters are incorporated. As a result, a variety of unique and high-resolution arbitrary shaped laser beams were generated with either a low or a high spatial coherence and with a minimal change in the laser output power. By controlling the phase, intensity, and coherence distributions, a shaped laser beam was efficiently reshaped into a completely different shape after free space propagation. The generation of such laser beams could lead to new and interesting applications.

  • Growth-Etch Metal–Organic Chemical Vapor Deposition Approach of WS2 Atomic Layers

    Cohen A., Patsha A., Mohapatra P. K., Kazes M., Ranganathan K., Houben L., Oron D. & Ismach A. (2021) ACS Nano.
    Metal–organic chemical vapor deposition (MOCVD) is one of the main methodologies used for thin-film fabrication in the semiconductor industry today and is considered one of the most promising routes to achieve large-scale and high-quality 2D transition metal dichalcogenides (TMDCs). However, if special measures are not taken, MOCVD suffers from some serious drawbacks, such as small domain size and carbon contamination, resulting in poor optical and crystal quality, which may inhibit its implementation for the large-scale fabrication of atomic-thin semiconductors. Here we present a growth-etch MOCVD (GE-MOCVD) methodology, in which a small amount of water vapor is introduced during the growth, while the precursors are delivered in pulses. The evolution of the growth as a function of the amount of water vapor, the number and type of cycles, and the gas composition is described. We show a significant domain size increase is achieved relative to our conventional process. The improved crystal quality of WS2 (and WSe2) domains wasis demonstrated by means of Raman spectroscopy, photoluminescence (PL) spectroscopy, and HRTEM studies. Moreover, time-resolved PL studies show very long exciton lifetimes, comparable to those observed in mechanically exfoliated flakes. Thus, the GE-MOCVD approach presented here may facilitate their integration into a wide range of applications.

  • Device-independent quantum key distribution from computational assumptions

    Metger T., Dulek Y., Coladangelo A. & Arnon-Friedman R. (2021) New journal of physics..
    In device-independent quantum key distribution (DIQKD), an adversary prepares a device consisting of two components, distributed to Alice and Bob, who use the device to generate a secure key. The security of existing DIQKD schemes holds under the assumption that the two components of the device cannot communicate with one another during the protocol execution. This is called the locality assumption in DIQKD. Here, we show how to replace this assumption, which can be hard to enforce in practice, by a standard computational assumption from post-quantum cryptography: we give a protocol that produces secure keys even when the components of an adversarial device can exchange arbitrary quantum communication, assuming the device is computationally bounded. Importantly, the computational assumption only needs to hold during the protocol execution---the keys generated at the end of the protocol are information-theoretically secure as in standard DIQKD protocols.

  • Undulator design for a laser-plasma-based free-electron-laser

    Ghaith A., Couprie M., Oumbarek-Espinos D., Andriyash I., Massimo F., Clarke J., Courthold M., Bayliss V., Bernhard A., Trunk M., Valléau M., Marcouillé O., Chancé A., Licciardi S., Malka V., Nguyen F. & Dattoli G. (2021) Physics Reports.
    The fourth generation of synchrotron radiation sources, commonly referred to as the Free Electron Laser (FEL), provides an intense source of brilliant X-ray beams enabling the investigation of matter at the atomic scale with unprecedented time resolution. These sources require the use of conventional linear accelerators providing high electron beam performance. The achievement of chirped pulse amplification allowing lasers to be operated at the Terawatt range, opened the way for the Laser Plasma Acceleration (LPA) technique where high energy electron bunches with high current can be produced within a very short centimeter-scale distance. Such an advanced acceleration concept is of great interest to be qualified by an FEL application for compact X-ray light sources. We explore in this paper what the LPA specificities imply on the design of the undulator, part of the gain medium. First, the LPA concept and state-of-art are presented showing the different operation regimes and what electron beam parameters are likely to be achieved. The LPA scaling laws are discussed afterwards to better understand what laser or plasma parameters have to be adjusted in order to improve electron beam quality. The FEL is secondly discussed starting with the spontaneous emission, followed by the different FEL configurations, the electron beam transport to the undulator and finally the scaling laws and correction terms in the high gain case. Then, the different types of compact undulators that can be implemented for an LPA based FEL application are analyzed. Finally, examples of relevant experiments are reported by describing the transport beamline, presenting the spontaneous emission characteristics achieved so far and the future prospects.

  • Upper Bounds on Device-Independent Quantum Key Distribution Rates and a Revised Peres Conjecture

    Arnon-Friedman R. & Leditzky F. (2021) IEEE transactions on information theory / Professional Technical Group on Information Theory..
    Device-independent quantum key distribution (DIQKD) is one of the most challenging tasks in quantum cryptography. The protocols and their security are based on the existence of Bell inequalities and the ability to violate them by measuring entangled states. We study the entanglement needed for DIQKD protocols in two different ways. Our first contribution is the derivation of upper bounds on the key rates of CHSH-based DIQKD protocols in terms of the violation of the inequality; this sets an upper limit on the possible DI key extraction rate from states with a given violation. Our upper bound improves on the previously known bound of Kaur et al. Our second contribution is the initiation of the study of the role of bound entangled states in DIQKD. We present a revised Peres conjecture stating that such states cannot be used as a resource for DIQKD. We give a first piece of evidence for the conjecture by showing that the bound entangled state found by Vertesi and Brunner, even though it can certify DI randomness, cannot be used to produce a key using protocols analogous to the well-studied CHSH-based DIQKD protocol.

  • Quantum Sensing and Control of Spin-State Dynamics in the Radical-Pair Mechanism

    Finkler A. & Dasari D. (2021) Physical Review Applied.
    Radical pairs and the dynamics they undergo are prevalent in many chemical and biological systems. Specifically, it has been proposed that the radical-pair mechanism results from a relatively strong hyperfine interaction with its intrinsic nuclear spin environment. While the existence of this mechanism is undisputed, the nanoscale details remain to be experimentally shown. Here, we analyze the role of a quantum sensor in detecting the spin dynamics (non-Markovian) of individual radical pairs in the presence of a weak magnetic field. We show how quantum control methods can be used to set apart the dynamics of the radical-pair mechanism at various stages of the evolution. We expect these findings to have implications to the understanding of the physical mechanism in magnetoreception and other biochemical processes with a microscopic detail.

  • Controlling Interactions between Quantum Emitters Using Atom Arrays

    Patti T. L., Wild D. S., Shahmoon E., Lukin M. D. & Yelin S. F. (2021) Physical review letters.
    We investigate the potential for two-dimensional atom arrays to modify the radiation and interaction of individual quantum emitters. Specifically, we demonstrate that control over the emission linewidths, resonant frequency shifts, and local driving field enhancement in impurity atoms is possible due to strong dipole-dipole interactions within ordered, subwavelength atom array configurations. We demonstrate that these effects can be used to dramatically enhance coherent dipole-dipole interactions between distant impurity atoms within an atom array. Possible experimental realizations and potential applications are discussed.

  • Observing Multiexciton Correlations in Colloidal Semiconductor Quantum Dots via Multiple-Quantum Two-Dimensional Fluorescence Spectroscopy

    Mueller S., Lüttig J., Brenneis L., Oron D. & Brixner T. (2021) ACS Nano.
    Correlations between excitons, that is, electron-hole pairs, have a great impact on the optoelectronic properties of semiconductor quantum dots and thus are relevant for applications such as lasers and photovoltaics. Upon multiphoton excitation, these correlations lead to the formation of multiexciton states. It is challenging to observe these states spectroscopically, especially higher multiexciton states, because of their short lifetimes and nonradiative decay. Moreover, solvent contributions in experiments with coherent signal detection may complicate the analysis. Here we employ multiple-quantum two-dimensional (2D) fluorescence spectroscopy on colloidal CdSe1-xS x /ZnS alloyed core/shell quantum dots. We selectively map the electronic structure of multiexcitons and their correlations by using two- and three-quantum 2D spectroscopy, conducted in a simultaneous measurement. Our experiments reveal the characteristics of biexcitons and triexcitons such as transition dipole moments, binding energies, and correlated transition energy fluctuations. We determine the binding energies of the first six biexciton states by simulating the two-quantum 2D spectrum. By analyzing the line shape of the three-quantum 2D spectrum, we find strong correlations between biexciton and triexciton states. Our method contributes to a more comprehensive understanding of multiexcitonic species in quantum dots and other semiconductor nanostructures.

  • Low frequency coherent Raman spectroscopy

    Bartels R., Oron D. & Rigneault H. (2021) Journal of Physics: Photonics.
    We revisit low frequency coherent Raman spectroscopy (LF-CRS) and present a unified theoretical background that provides consistent physical pictures of LF-CRS signal generation. Our general framework allows to compute the signal to noise ratio in the multitude of possible LF-CRS, and more generally CRS, experimental implementations both in the spectral and time domain.

  • cSPARCOM: Multi-detector reconstruction by confocal super-resolution correlation microscopy

    Rossman U., Dadosh T., Eldar Y. & Oron D. (2021) Optics Express.
    Image scanning microscopy (ISM), an upgraded successor of the ubiquitous confocal microscope, facilitates up to two-fold improvement in lateral resolution, and has become an indispensable element in the toolbox of the bio-imaging community. Recently, super-resolution optical fluctuation image scanning microscopy (SOFISM) integrated the analysis of intensity-fluctuations information into the basic ISM architecture, to enhance its resolving power. Both of these techniques typically rely on pixel-reassignment as a fundamental processing step, in which the parallax of different detector elements to the sample is compensated by laterally shifting the point spread function (PSF). Here, we propose an alternative analysis approach, based on the recent high-performing sparsity-based super-resolution correlation microscopy (SPARCOM) method. Through measurements of DNA origami nano-rulers and fixed cells labeled with organic dye, we experimentally show that confocal SPARCOM (cSPARCOM), which circumvents pixel-reassignment altogether, provides enhanced resolution compared to pixel-reassigned based analysis. Thus, cSPARCOM further promotes the effectiveness of ISM, and particularly that of correlation based ISM implementations such as SOFISM, where the PSF deviates significantly from spatial invariance.

  • Attosecond technology(ies) and science

    Biegert J., Calegari F., Dudovich N., Quéré F. & Vrakking M. (2021) Journal of physics. B, Atomic, molecular, and optical physics.
    Since 2001 and the first demonstrations of the feasibility of generating and measuring attosecond light pulses, attosecond science has developed into a very active and quickly evolving research field. Its ultimate goal is the real-time tracking of electron dynamics in all forms of matter, ranging from atoms and large molecules to the condensed phase and plasmas. The accomplishment of this goal has required and still calls for developments in ultrafast laser technology, ultrafast metrology, extreme ultra-violet (XUV) optics, pump–probe measurement schemes and non-linear laser-matter interaction. Moreover, the interpretation of the experimental results in attosecond experiments has stimulated and guided major developments in theoretical descriptions of ultrafast electronic processes in matter. Motivated by these two decades of development, several large-scale facilities, including extreme light infrastructure—attosecond light pulse source (ELI-ALPS) and several free electron laser facilities (the linac coherent light source (LCLS) at Stanford and the European XFEL in Hamburg) are now pushing the development of a new generation of attosecond sources. This considerable technological effort opens new and important perspectives in the field of ultrafast science with potential applications in photochemistry, photobiology and advanced electronics. In this context, the joint focus issue on Attosecond technology(/ies) and science of J. Phys. Photon. and J. Phys. B: At. Mol. Opt. Phys. aims to provide an overview of the state-of-the-art in attosecond science, from the basic science involved in the generation and in applications of attosecond pulses to the technologies that are required.

  • Fast laser speckle suppression with an intracavity diffuser

    Mahler S., Eliezer Y., Yılmaz H., Friesem A. A., Davidson N. & Cao H. (2021) .
    Fast speckle suppression is crucial for time-resolved full-field imaging with laser illumination. Here, we introduce a method to accelerate the spatial decoherence of laser emission, achieving speckle suppression in the nanosecond integration time scale. The method relies on the insertion of an intracavity phase diffuser into a degenerate cavity laser to break the frequency degeneracy of transverse modes and broaden the lasing spectrum. The ultrafast decoherence of laser emission results in the reduction of speckle contrast to 3% in less than 1 ns.

  • Observation of nonlinear spin dynamics and squeezing in a BEC using dynamic decoupling

    Edri H., Raz B., Fleurov G., Ozeri R. & Davidson N. (2021) New Journal of Physics.
    We study the evolution of a Bose–Einstein condensate in a two-state superposition due to inter-state interactions. Using a population imbalanced dynamic decoupling scheme, we measure inter-state interactions while canceling intra-state density shifts and external noise sources. Our measurements show low statistical uncertainties for both magnetic sensitive and insensitive superpositions, indicating that we successfully decoupled our system from strong magnetic noises. We experimentally show that the Bloch sphere representing general superposition states is 'twisted' by inter-state interactions, as predicted in [1, 2] and the twist rate depends on the difference between inter-state and intra-state scattering lengths a22 + a11 − 2a12. We use the non-linear spin dynamics to demonstrate squeezing of Gaussian noise, showing 2.79 ± 0.43 dB squeezing when starting with a noisy state and applying 160 echo pulses, which can be used to increase sensitivity when there are errors in state preparation. Our results allow for a better understanding of inter-atomic potentials in 87Rb. Our scheme can be used for spin-squeezing beyond the standard quantum limit and observing polaron physics close to Feshbach resonances, where interactions diverge, and strong magnetic noises are ever present.

  • Work Generation from Thermal Noise by Quantum Phase-Sensitive Observation

    Opatrný T., Misra A. & Kurizki G. (2021) Physical review letters.
    We put forward the concept of work extraction from thermal noise by phase-sensitive (homodyne) measurements of the noisy input followed by (outcome-dependent) unitary manipulations of the postmeasured state. For optimized measurements, noise input with more than one quantum on average is shown to yield heat-to-work conversion with efficiency and power that grow with the mean number of input quanta, the efficiency and the inverse temperature of the detector. This protocol is shown to be advantageous compared to common models of information and heat engines

  • Boosting photonic quantum computation with moderate nonlinearity

    Pick A., Siddiqui-Matekole E., Aqua Z., Guendelman G., Firstenberg O., Dowling J. P. & Dayan B. (2021) Physical Review Applied.
    Photonic measurement-based quantum computation (MBQC) is a promising route towards fault-tolerant universal quantum computing. A central challenge in this effort is the huge overhead in the resources required for the construction of large photonic clusters using probabilistic linear-optics gates. Although strong single-photon nonlinearity ideally enables deterministic construction of such clusters, it is challenging to realise in a scalable way. Here we explore the prospects of using moderate nonlinearity (with conditional phase shifts smaller than π ) to boost photonic quantum computing and significantly reduce its resources’ overhead. The key element in our scheme is a nonlinear router that preferentially directs photonic wavepackets to different output ports depending on their intensity. As a relevant example, we analyze the nonlinearity provided by Rydberg blockade in atomic ensembles, in which the trade-off between the nonlinearity and the accompanying loss is well understood. We present protocols for efficient Bell measurement and GHZ-state preparation—both key elements in the construction of cluster states, as well as for the cnot gate and quantum factorization. Given the large number of entangling operations involved in fault-tolerant MBQC, the increase in success probability provided by our protocols already at moderate nonlinearities can result in a significant reduction in the required resources.

  • High-energy-resolution measurement of ultracold atom-ion collisional cross section

    Ben-shlomi R., Pinkas M., Meir Z., Sikorsky T., Katz O., Akerman N. & Ozeri R. (2021) Physical review. A, Atomic, molecular, and optical physics..
    The cross section of a given process fundamentally quantifies the probability for that given process to occur. In the quantum regime of low energies, the cross section can vary strongly with collision energy due to quantum effects. Here, we report on a method to directly measure the atom-ion collisional cross section in the energy range of 0.2-12 mK$\cdot$ k$_B$, by shuttling ultracold atoms trapped in an optical-lattice across a radio-frequency trapped ion. In this method, the average number of atom-ion collisions per experiment is below one such that the energy resolution is not limited by the broad (power-law) steady-state atom-ion energy distribution. Here, we estimate that the energy resolution is below 200 $\mu$K$\cdot$k$_B$, limited by drifts in the ion's excess micromotion compensation and can be reduced to the 10's $\mu$K$\cdot$k$_B$ regime. This resolution is one order-of-magnitude better than previous experiments measuring cold atom-ion collisional cross section energy dependence. We used our method to measure the energy dependence of the inelastic collision cross sections of a non-adiabatic Electronic-Excitation-Exchange (EEE) and Spin-Orbit Change (SOC) processes. We found that in the measured energy range, the EEE and SOC cross sections statistically agree with the classical Langevin cross section. This method allows for measuring the cross sections of various inelastic processes and opens up possibilities to search for atom-ion quantum signatures such as shape-resonances.

  • Cosmological horizons radiate

    Leonhardt U. (2021) Europhysics Letters.
    Gibbons and Hawking [Phys. Rev. D 15, 2738 (1977)] have shown that the horizon of de Sitter space emits radiation in the same way as the event horizon of the black hole. But actual cosmological horizons are not event horizons, except in de Sitter space. Nevertheless, this paper proves Gibbons' and Hawking's radiation formula as an exact result for any flat space expanding with strictly positive Hubble parameter. The paper gives visual and intuitive insight into why this is the case. The paper also indicates how cosmological horizons are related to the dynamical Casimir effect, which makes experimental tests with laboratory analogues possible.

  • Conceptual Design Report for the LUXE Experiment

    Abramowicz H., Davidi O., Malka V., Perez G. & Hod N. T. (2021) arXiv.
    This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) effective field strengths to be probed at and beyond the Schwinger limit and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 300 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout.

  • Nonlinear interferometry enables coherent heat machine operation

    Opatrný T., Bräuer Š., Kofman A. G., Misra A., Meher N., Firstenberg O., Poem E. & Kurizki G. (2021) arXiv.org.
    We propose a novel principle of operating heat machines in a fully unitary (coherent) fashion by mixing few hot and cold thermal field modes in nonlinear interferometers. Such devices, specifically, interferometers containing Kerr-nonlinear intermode cross-couplers, are shown to enable autonomous concentration of the energy predominantly in a desired output mode, at the expense of the other modes. Their phase-coherent operation is reversible and it is approximately reversible even if intermode entanglement is neglected. Such few-mode coherent heat machines radically depart from the existing thermodynamic paradigm which treats heat machines as open systems dissipated by heat baths.

  • Continuous Protection of a Collective State from Inhomogeneous Dephasing

    Finkelstein R., Lahad O., Cohen I., Davidson O., Kiriati S., Poem E. & Firstenberg O. (2021) Physical Review X.
    We introduce and demonstrate a scheme for eliminating the inhomogeneous dephasing of a collective quantum state. The scheme employs off-resonant fields that continuously dress the collective state with an auxiliary sensor state, which has an enhanced and opposite sensitivity to the same source of inhomogeneity. We derive the optimal conditions under which the dressed state is fully protected from dephasing when using either one or two dressing fields. The latter provides better protection, circumvents qubit phase rotation, and suppresses the sensitivity to drive noise. We further derive expressions for all residual, higher-order sensitivities. We experimentally study the scheme by protecting a collective excitation of an atomic ensemble, where inhomogeneous dephasing originates from thermal motion. Using photon storage and retrieval, we demonstrate complete suppression of inhomogeneous dephasing and, consequently, a prolonged memory time. Our scheme may be applied to eliminate motional dephasing in other systems, improving the performance of quantum gates and memorieswith neutral atoms. It is also generally applicable to various gas, solid, and engineered systems, where sensitivity to variations in time, space, or other domains limits possible scale-up of the system.

  • On the thermodynamics of the difference between energy transfer rate and heat engine efficiency

    Dong H., Ghosh A., Kim M. B., Li S., Svidzinsky A. A., Zhang Z., Kurizki G. & Scully M. O. (2021) The European physical journal. ST, Special topics.
    We study the difference between the energy transfer rate and the engine efficiency with a microscopic model, widely used in the theoretical description of solar cells, as well as in light-harvesting systems. We show no violation of the second law of thermodynamics by correctly assessing the useful output work, even with the simple model treating the later work conversion as a simple “sink”.

  • Control and enhancement of multiband high harmonic generation by synthesized laser fields

    Bruner B. D., Narovlansky-Uzan A. J., Arusi-Parpar T., Orenstein G., Shonfeld A. & Dudovich N. (2021) Journal of physics. B, Atomic, molecular, and optical physics.
    High harmonic generation (HHG) spectroscopy has emerged as an invaluable tool for studying electronic dynamics and structure in crystals. The primary challenges are imposed by the multiple degrees of freedom of the underlying dynamics as well as the low efficiency of the HHG process. Here we show that when the HHG process is driven by a synthesized bichromatic field, its efficiency can be significantly enhanced, increasing the photon flux by 1–2 orders of magnitude. The bichromatic field enhances the signal on a microscopic level by manipulating the tunnel ionization and subsequent electron dynamics driven by the synthesized laser waveform. We examine the scaling of the HHG yield on the field parameters, and observe a pronounced dependence on the HHG energy. Importantly, our study reveals that the different spectral regimes are dictated by different generation mechanisms as well as multiple bands in which the dynamics evolve. Our work demonstrates that shaped laser fields serve as a powerful approach to control multiband electron currents in solids, probe their origin, and enhance the efficiency of the HHG process.

  • Lifshitz cosmology: quantum vacuum and Hubble tension

    Berechya D. & Leonhardt U. (2021) Monthly notices of the Royal Astronomical Society.
    Dark energy is one of the greatest scientific mysteries of today. The idea that dark energy originates from quantum vacuum fluctuations has circulated since the late '60s, but theoretical estimations of vacuum energy have disagreed with the measured value by many orders of magnitude, until recently. Lifshitz theory applied to cosmology has produced the correct order of magnitude for dark energy. Furthermore, the theory is based on well-established and experimentally well-tested grounds in atomic, molecular and optical physics. In this paper, we confront Lifshitz cosmology with astronomical data. We find that the dark-energy dynamics predicted by the theory is able to resolve the Hubble tension, the discrepancy between the observed and predicted Hubble constant within the standard cosmological model. The theory is consistent with supernovae data, Baryon Acoustic Oscillations and the Cosmic Microwave Background. Our findings indicate that Lifshitz cosmology is a serious candidate for explaining dark energy.

  • Space- and time-resolved second harmonic spectroscopy of coupled plasmonic nanocavities

    Salomon A., Kollmann H., Mascheck M., Schmidt S., Prior Y., Lienau C. & Silies M. (2021) Nanophotonics (Berlin, Germany).
    Localized surface plasmon resonances of individual sub-wavelength cavities milled in metallic films can couple to each other to form a collective behavior. This coupling leads to a delocalization of the plasmon field at the film surface and drastically alters both the linear and nonlinear optical properties of the sample. In periodic arrays of nanocavities, the coupling results in the formation of propagating surface plasmon polaritons (SPP), eigenmodes extending across the array. When artificially introducing dislocations, defects and imperfections, multiple scattering of these SPP modes can lead to hot-spot formation, intense and spatially confined fluctuations of the local plasmonic field within the array. Here, we study the underlying coupling effects by probing plasmonic modes in well-defined individual triangular dimer cavities and in arrays of triangular cavities with and without artificial defects. Nonlinear confocal spectro-microscopy is employed to map the second harmonic (SH) radiation from these systems. Pronounced spatial localization of the SPP field and significant enhancements of the SH intensity in certain, randomly distributed hot spots by more than an order of magnitude are observed from the triangular arrays as compared to a bare silver film by introducing a finite degree of disorder into the array structure. Hot-spot formation and the resulting enhancement of the nonlinear efficiency are correlated with an increase in the lifetime of the localized SPP modes. By using interferometric SH autocorrelation measurements, we reveal lifetimes of hot-spot resonances in disordered arrays that are much longer than the few-femtosecond lifetimes of the localized surface plasmon resonances of individual nanocavity dimers. This suggests that hot spot lifetime engineering provides a path for manipulating the linear and nonlinear optical properties of nanosystems by jointly exploiting coherent couplings and tailored disorder.

  • Echoes in a single quantum Kerr-nonlinear oscillator

    Tutunnikov I., Rajitha K. V. & Averbukh I. S. (2021) Physical Review A.
    A quantum Kerr-nonlinear oscillator is a paradigmatic model in cavity and circuit quantum electrodynamics, and quantum optomechanics. We theoretically study the echo phenomenon in a single impulsively excited ("kicked") Kerr-nonlinear oscillator. We reveal two types of echoes, "quantum"and "classical"ones, emerging on the long and short time scales, respectively. The mechanisms of the echoes are discussed, and their sensitivity to dissipation is considered. These echoes may be useful for studying decoherence processes in a number of systems related to quantum information processing.

  • Direct measurement of Coulomb-laser coupling

    Azoury D., Krüger M., Bruner B. D., Smirnova O. & Dudovich N. (2021) Scientific Reports.
    The Coulomb interaction between a photoelectron and its parent ion plays an important role in a large range of light-matter interactions. In this paper we obtain a direct insight into the Coulomb interaction and resolve, for the first time, the phase accumulated by the laser-driven electron as it interacts with the Coulomb potential. Applying extreme-ultraviolet interferometry enables us to resolve this phase with attosecond precision over a large energy range. Our findings identify a strong laser-Coulomb coupling, going beyond the standard recollision picture within the strong-field framework. Transformation of the results to the time domain reveals Coulomb-induced delays of the electrons along their trajectories, which vary by tens of attoseconds with the laser field intensity.

  • Thermodynamic bounds on work extraction from photocells and photosynthesis

    Dong H., Ghosh A., Scully M. O. & Kurizki G. (2021) The European physical journal. ST, Special topics.
    We put forward a unified thermodynamic analysis of generic minimal models of solar-powered cyclic processes that can be viewed as quantum heat engines. The resulting general efficiency bound for work production is consistent with the second law of thermodynamics if it allows for heat and entropy generation. This bound is shown to interpolate between the Carnot and the Shockley–Queisser bounds. Power boost induced by coherence or multiexciton generation does not affect the efficiency. These features may allow us to design solar-pumped schemes that are optimal, both energetically and operationally.

  • Control of concerted back-to-back double ionization dynamics in helium

    Larsson H. R. & Tannor D. J. (2021) The Journal of chemical physics.
    Double ionization (DI) is a fundamental process that despite its apparent simplicity provides rich opportunities for probing and controlling the electronic motion. Even for the simplest multielectron atom, helium, new DI mechanisms are still being found. To first order in the field strength, a strong external field doubly ionizes the electrons in helium such that they are ejected into the same direction (front-to-back motion). The ejection into opposite directions (back-to-back motion) cannot be described to first order, making it a challenging target for control. Here, we address this challenge and optimize the field with the objective of back-to-back double ionization using a (1 + 1)-dimensional model. The optimization is performed using four different control procedures: (1) short-time control, (2) derivative-free optimization of basis expansions of the field, (3) the Krotov method, and (4) control of the classical equations of motion. All four procedures lead to fields with dominant back-to-back motion. All the fields obtained exploit essentially the same two-step mechanism leading to back-to-back motion: first, the electrons are displaced by the field into the same direction. Second, after the field turns off, the nuclear attraction and the electron-electron repulsion combine to generate the final motion into opposite directions for each electron. By performing quasi-classical calculations, we confirm that this mechanism is essentially classical. .

  • Device-Independent Quantum Information Processing: A Simplified Analysis

    Arnon-Friedman R. (2020) .
    Device-independent quantum cryptography is a method for exchanging secret messages over potentially insecure quantum communication channels, such as optical fibers. In contrast to conventional quantum cryptography, security is guaranteed even if the devices used by the communication partners, such as photon sources and detectors, deviate from their theoretical specifications. This is of high practical relevance, for attacks to current implementations of quantum cryptography exploit exactly such deviations. Device-independent cryptography is however technologically so demanding that it looked as if experimental realizations are out of reach.In her thesis, Rotem Arnon-Friedman presents powerful information-theoretic methods to prove the security of device-independent quantum cryptography. Based on them, she is able to establish security in a parameter regime that may be experimentally achievable in the near future. Rotem Arnon-Friedman's thesis thus provides the theoretical foundations for an experimental demonstration of device-independent quantum cryptography.

  • Bayesian optimization for inverse problems in time-dependent quantum dynamics

    Deng Z., Tutunnikov I., Averbukh I. S., Thachuk M. & Krems R. V. (2020) Journal of Chemical Physics.
    We demonstrate an efficient algorithm for inverse problems in time-dependent quantum dynamics based on feedback loops between Hamiltonian parameters and the solutions of the Schrödinger equation. Our approach formulates the inverse problem as a target vector estimation problem and uses Bayesian surrogate models of the Schrödinger equation solutions to direct the optimization of feedback loops. For the surrogate models, we use Gaussian processes with vector outputs and composite kernels built by an iterative algorithm with the Bayesian information criterion (BIC) as a kernel selection metric. The outputs of the Gaussian processes are designed to model an observable simultaneously at different time instances. We show that the use of Gaussian processes with vector outputs and the BIC-directed kernel construction reduces the number of iterations in the feedback loops by, at least, a factor of 3. We also demonstrate an application of Bayesian optimization for inverse problems with noisy data. To demonstrate the algorithm, we consider the orientation and alignment of polyatomic molecules SO2 and propylene oxide (PPO) induced by strong laser pulses. We use simulated time evolutions of the orientation or alignment signals to determine the relevant components of the molecular polarizability tensors. We show that, for the five independent components of the polarizability tensor of PPO, this can be achieved with as few as 30 quantum dynamics calculations.

  • EuPRAXIA Conceptual Design Report

    Assmann R. W., Weikum M. K., Akhter T., Alesini D., Alexandrova A. S., Anania M. P., Andreev N. E., Andriyash I., Artioli M., Aschikhin A., Audet T., Bacci A., Barna I. F., Bartocci S., Bayramian A., Beaton A., Bellaveglia M., Beluze A., Bernhard A., Biagioni A., Bielawski S., Bisesto F. G., Bonatto A., Boulton L., Brandi F., Brinkmann R., Briquez F., Brottier F., Bründermann E., Büscher M., Buonomo B., Bussmann M. H., Bussolino G., Campana P., Cantarella S., Cassou K., Chancé A., Chen M., Chiadroni E., Cianchi A., Cioeta F., Clarke J. A., Cole J. M., Costa G., Couprie M. E., Cowley J., Croia M., Cros B., Crump P. A., D’Arcy R., Dattoli G., Del Dotto A., Delerue N., Del Franco M., Delinikolas P., De Nicola S., Dias J. M., Di Giovenale D., Diomede M., Di Pasquale E., Di Pirro G., Di Raddo G., Dorda U., Erlandson A. C., Ertel K., Esposito A., Falcoz F., Falone A., Fedele R., Ferran Pousa A., Ferrario M., Filippi F., Fils J., Fiore G., Fiorito R., Fonseca R. A., Franzini G., Galimberti M., Gallo A., Galvin T. C., Ghaith A., Ghigo A., Giove D., Giribono A., Gizzi L. A., Grüner F. J., Habib A. F., Haefner C., Heinemann T., Helm A., Hidding B., Holzer B. J., Hooker S. M., Hosokai T., Hübner M., Ibison M., Incremona S., Irman A., Iungo F., Jafarinia F. J., Jakobsson O., Jaroszynski D. A., Jaster-Merz S., Joshi C., Kaluza M., Kando M., Karger O. S., Karsch S., Khazanov E., Khikhlukha D., Kirchen M., Kirwan G., Kitégi C., Knetsch A., Kocon D., Koester P., Kononenko O. S., Korn G., Kostyukov I., Kruchinin K. O., Labate L., Le Blanc C., Lechner C., Lee P., Leemans W., Lehrach A., Li Y., Libov V., Lifschitz A., Lindstrøm C. A., Litvinenko V., Lu W., Lundh O., Maier A. R., Malka V., Manahan G. G., Mangles S. P., Marcelli A., Marchetti B., Marcouillé O., Marocchino A., Marteau F., Martinez de la Ossa A., Martins J. L., Mason P. D., Massimo F., Mathieu F., Maynard G., Mazzotta Z., Mironov S., Molodozhentsev A. Y., Morante S., Mosnier A., Mostacci A., Müller A. S., Murphy C. D., Najmudin Z., Nghiem P. A., Nguyen F., Niknejadi P., Nutter A., Osterhoff J., Oumbarek Espinos D., Paillard J. L., Papadopoulos D. N., Patrizi B., Pattathil R., Pellegrino L., Petralia A., Petrillo V., Piersanti L., Pocsai M. A., Poder K., Pompili R., Pribyl L., Pugacheva D., Reagan B. A., Resta-Lopez J., Ricci R., Romeo S., Rossetti Conti M., Rossi A. R., Rossmanith R., Rotundo U., Roussel E., Sabbatini L., Santangelo P., Sarri G., Schaper L., Scherkl P., Schramm U., Schroeder C. B., Scifo J., Serafini L., Sharma G., Sheng Z. M., Shpakov V., Siders C. W., Silva L. O., Silva T., Simon C., Simon-Boisson C., Sinha U., Sistrunk E., Specka A., Spinka T. M., Stecchi A., Stella A., Stellato F., Streeter M. J., Sutherland A., Svystun E. N., Symes D., Szwaj C., Tauscher G. E., Terzani D., Toci G., Tomassini P., Torres R., Ullmann D., Vaccarezza C., Valléau M., Vannini M., Vannozzi A., Vescovi S., Vieira J. M., Villa F., Wahlström C. G., Walczak R., Walker P. A., Wang K., Welsch A., Welsch C. P., Weng S. M., Wiggins S. M., Wolfenden J., Xia G., Yabashi M., Zhang H., Zhao Y., Zhu J. & Zigler A. (2020) European Physical Journal: Special Topics.
    This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.

  • Long-Lived Entanglement Generation of Nuclear Spins Using Coherent Light

    Katz O., Shaham R., Polzik E. S. & Firstenberg O. (2020) Physical Review Letters.
    Nuclear spins of noble-gas atoms are exceptionally isolated from the environment and can maintain their quantum properties for hours at room temperature. Here we develop a mechanism for entangling two such distant macroscopic ensembles by using coherent light input. The interaction between the light and the noble-gas spins in each ensemble is mediated by spin-exchange collisions with alkali-metal spins, which are only virtually excited. The relevant conditions for experimental realizations with He3 or Xe129 are outlined.

  • Echoes in unidirectionally rotating molecules

    Xu L., Tutunnikov I., Zhou L., Lin K., Qiang J., Lu P., Prior Y., Averbukh I. S. & Wu J. (2020) Physical Review A.
    We report the experimental observation of molecular unidirectional rotation (UDR) echoes and analyze their origin and behavior both classically and quantum mechanically. The molecules are excited by two time-delayed polarization-twisted ultrashort laser pulses and the echoes are measured by exploding the molecules and reconstructing their spatial orientation from the detected recoil ions momenta. Unlike alignment echoes which are induced by linearly polarized pulses, here the axial symmetry is broken by the twisted polarization, giving rise to molecular unidirectional rotation. We find that the rotation sense of the echo is governed by the twisting sense of the second pulse even when its intensity is much weaker than the intensity of the first pulse. In our theoretical study, we rely on classical phase-space analysis and on three-dimensional quantum simulations of the laser-driven molecular dynamics. Both approaches nicely reproduce the experimental results. Echoes in general and the unique UDR echoes in particular provide powerful tools for studies of relaxation processes in dense molecular gases.

  • Error-corrected gates on an encoded qubit

    Reinhold P., Rosenblum S., Ma W., Frunzio L., Jiang L. & Schoelkopf R. J. (2020) Nature Physics.
    To reach their full potential, quantum computers need to be resilient to noise and decoherence. In such a fault-tolerant quantum computer, errors must be corrected in real time to prevent them from propagating between components(1,2). This requirement is especially pertinent while applying quantum gates, where the interaction between components can cause errors to spread quickly throughout the system. However, the large overhead involved in most fault-tolerant architectures(2,3) makes implementing these systems a daunting task, motivating the search for hardware-efficient alternatives(4,5). Here, we present a gate enacted by an ancilla transmon on a cavity-encoded logical qubit that is fault-tolerant to ancilla decoherence and compatible with logical error correction. We maintain the purity of the encoded qubit by correcting ancilla-induced errors in real time, yielding a reduction of the logical gate error by a factor of two in the presence of naturally occurring decoherence. We also demonstrate a sixfold suppression of the gate error with increased ancilla relaxation errors and a fourfold suppression with increased ancilla dephasing errors. The results demonstrate that bosonic logical qubits can be controlled by error-prone ancilla qubits without inheriting the ancilla's inferior performance. As such, error-corrected ancilla-enabled gates are an important step towards fault-tolerant processing of bosonic qubits.Error-corrected quantum gates that can tolerate dominant errors during the execution of quantum operations have been demonstrated. Substantial improvement of the gate fidelity sheds light on fault-tolerant universal quantum computation.

  • Identification of molecular quantum states using phase-sensitive forces

    Najafian K., Meir Z., Sinhal M. & Willitsch S. (2020) Nature Communications.
    Quantum-logic techniques used to manipulate quantum systems are now increasingly being applied to molecules. Previous experiments on single trapped diatomic species have enabled state detection with excellent fidelities and highly precise spectroscopic measurements. However, for complex molecules with a dense energy-level structure improved methods are necessary. Here, we demonstrate an enhanced quantum protocol for molecular state detection using state-dependent forces. Our approach is based on interfering a reference and a signal force applied to a single atomic and molecular ion. By changing the relative phase of the forces, we identify states embedded in a dense molecular energy-level structure and monitor state-to-state inelastic scattering processes. This method can also be used to exclude a large number of states in a single measurement when the initial state preparation is imperfect and information on the molecular properties is incomplete. While the present experiments focus on N2+, the method is general and is expected to be of particular benefit for polyatomic systems.

  • Giant polarization drag in a gas of molecular super-rotors

    Steinitz U. & Averbukh I. S. (2020) Physical Review A.
    Experiments on light dragging in a moving medium laid the cornerstones of modern physics more than a century ago, and they still are in the focus of current research. When linearly polarized light is transmitted through a rotating dielectric, the polarization plane is slightly rotated-a phenomenon first studied by Fermi in 1923. For typical nonresonant dielectric materials, the measured polarization drag angle does not surpass several microradians. Here, we show that this effect may be dramatically enhanced if the light is sent to a gas of fast unidirectionally spinning molecular super-rotors. Several femtosecond-laser labs have already succeeded in optically creating such a medium. We show that the specific rotation power of the super-rotor medium exceeds the values previously observed in mechanically rotated bulk optical specimens by many orders of magnitude. This nonreciprocal optomechanical phenomenon may open other avenues for ultrafast control of the polarization state of light.

  • Evidence for laser-induced homogeneous oriented ice nucleation revealed via pulsed x-ray diffraction

    Nevo I., Jahn S., Kretzschmar N., Levantino M., Feldman Y., Naftali N., Wulff M., Oron D. & Leiserowitz L. (2020) Journal of Chemical Physics.
    The induction of homogeneous and oriented ice nucleation has to date not been achieved. Here, we report induced nucleation of ice from millimeter sized supercooled water drops illuminated by ns-optical laser pulses well below the ionization threshold making use of particular laser beam configurations and polarizations. Employing a 100 ps synchrotron x-ray pulse 100 ns after each laser pulse, an unambiguous correlation was observed between the directions and the symmetry of the laser fields and that of the H-bonding arrays of the induced ice crystals. Moreover, an analysis of the x-ray diffraction data indicates that, in the main, the induced nucleation of ice is homogeneous at temperatures well above the observed and predicted values for supercooled water.

  • Development of Lipid-Coated Semiconductor Nanosensors for Recording of Membrane Potential in Neurons

    Ludwig A., Serna P. A., Morgenstein L., Yang G., Bar-Elli O., Ortiz G., Miller E., Oron D., Grupi A., Weiss S. & Antoine T. (2020) ACS Photonics.
    In the past decade, optical imaging methods have significantly improved our understanding of the information processing principles in the brain. Although many promising tools have been designed, sensors of membrane potential are lagging behind the rest. Semiconductor nanoparticles are an attractive alternative to classical voltage indicators, such as voltage-sensitive dyes and proteins. Such nanoparticles exhibit high sensitivity to external electric fields via the quantum-confined Stark effect. Here we report the development of semiconductor voltage-sensitive nanorods (vsNRs) that self-insert into the neuronal membrane. To facilitate interaction of the nanorods with the membrane, we functionalized their surface with the lipid mixture derived from brain extract. We describe a workflow to detect and process the photoluminescent signal of vsNRs after wide-field time-lapse recordings. We also present data indicating that vsNRs are feasible for sensing membrane potential in neurons at a single-particle level. This shows the potential of vsNRs for the detection of neuronal activity with unprecedentedly high spatial and temporal resolution.

  • Boosting few-cycle soliton self-frequency shift using negative prechirp

    Rosenberg Y., Drori J., Bermudez D. & Leonhardt U. (2020) Optics Express.
    Soliton self-frequency shifting of light pulses in fibers is used for versatile tunable light sources. Few-cycle pulses of high soliton number offer unique advantages, in particular the rate of Raman frequency shift is extremely fast. However, their dynamics is complicated, which makes the optimization of the frequency shifting difficult and sometimes counter-intuitive. We performed a systematic experimental study of the effects of initial prechirp for different pulse energies (for two different fibers). We found that a negative prechirp around C=-0.75 is the most effective (C being the chirp parameter). With such prechirping we managed to cross the severe OH absorption bands of nonlinear photonic crystal fibers. The mechanism behind the effectiveness of the prechirp appears to be the power distribution between the products of soliton fission.

  • Weak-to-strong transition of quantum measurement in a trapped-ion system

    Pan Y., Zhang J., Cohen E., Wu C. w., Chen P. X. & Davidson N. (2020) Nature Physics.
    Quantum measurement remains a puzzle through its stormy history from the birth of quantum mechanics to state-of-the-art quantum technologies. Two complementary measurement schemes have been widely investigated in a variety of quantum systems: von Neumann’s projective ‘strong’ measurement and Aharonov’s weak measurement. Here, we report the observation of a weak-to-strong measurement transition in a single trapped <sup>40</sup>Ca<sup>+</sup> ion system. The transition is realized by tuning the interaction strength between the ion’s internal electronic state and its vibrational motion, which play the roles of the measured system and the measuring pointer, respectively. By pre- and post-selecting the internal state, a pointer state composed of two of the ion’s motional wavepackets is obtained, and its central-position shift, which corresponds to the measurement outcome, demonstrates the transition from the weak-value asymptotes to the expectation-value asymptotes. Quantitatively, the weak-to-strong measurement transition is characterized by a universal transition factor e−Γ2/2, where Γ is a dimensionless parameter related to the system–apparatus coupling. This transition, which continuously connects weak measurements and strong measurements, may open new experimental possibilities to test quantum foundations and prompt us to re-examine and improve the measurement schemes of related quantum technologies.

  • Theory of cavity QED with 2D atomic arrays

    Shahmoon E., Wild D. S., Lukin M. D. & Yelin S. F. (2020) arXiv.
    We develop a quantum optical formalism to treat a two-dimensional array of atoms placed in an optical cavity. Importantly, and in contrast to typical treatments, we account for cooperative dipole-dipole effects mediated by the interaction of the atoms with the outside, non-cavity-confined modes. Based on the observation that scattering to these modes is largely inhibited due to these cooperative effects, we construct a generic formalism, independent of the specific cavity structure, and apply it to an array of non-saturated atoms. By further considering the atomic motion, we show that the inhibited damping can lead to a favorable scaling of the optomechanical parameters of an atom-array membrane placed within a cavity. The developed formalism lays the basis for further investigation of many-body QED with atom arrays in transversely confined geometries.

  • Direct reconstruction of the quantum-master-equation dynamics of a trapped-ion qubit

    Ben Av E., Shapira Y., Akerman N. & Ozeri R. (2020) Physical Review A.
    The physics of Markovian open quantum systems can be described by quantum master equations. These are dynamical equations that incorporate the Hamiltonian and jump operators and generate the system's time evolution. Reconstructing the system's Hamiltonian and its coupling to the environment from measurements is important both for fundamental research and for performance evaluation of quantum machines. Here we introduce a method that reconstructs the dynamical equation of open quantum systems, directly from a set of expectation values of selected observables. We benchmark our technique both by a simulation and experimentally, by measuring the dynamics of a trapped Sr-88(+) ion qubit under spontaneous photon scattering.

  • Optical protection of a collective state from inhomogeneous dephasing

    Finkelstein R., Lahad O., Cohen I., Davidson O., Kiriati S., Poem E. & Firstenberg O. (2020) arXiv.
    We introduce and demonstrate a scheme for eliminating the inhomogeneous dephasing of a collective quantum state. The scheme employs off-resonant optical fields that dress the collective state with an auxiliary sensor state, which has an enhanced and opposite sensitivity to the same source of inhomogeneity. We derive the optimal conditions under which the dressed state is fully protected from dephasing, when using either one or two dressing fields. The latter provides better protection, prevents global phase rotation, and suppresses the sensitivity to drive noise. We further provide expressions for all residual, higher-order, sensitivities. We experimentally study the scheme by protecting a collective excitation of an atomic ensemble, where inhomogeneous dephasing originates from thermal motion. Using photon storage and retrieval, we demonstrate complete suppression of inhomogeneous dephasing and consequently a prolonged memory time. Our scheme may be applied to eliminate motional dephasing in other systems, improving the performance of quantum gates and memories with neutral atoms. It is also generally applicable to various gas, solid, and engineered systems, where sensitivity to variations in time, space, or other domains limits possible scale-up of the system.

  • Synchronization of complex human networks

    Shahal S., Wurzberg A., Sibony I., Duadi H., Shniderman E., Weymouth D., Davidson N. & Fridman M. (2020) Nature Communications.
    The synchronization of human networks is essential for our civilization and understanding its dynamics is important to many aspects of our lives. Human ensembles were investigated, but in noisy environments and with limited control over the network parameters which govern the network dynamics. Specifically, research has focused predominantly on all-to-all coupling, whereas current social networks and human interactions are often based on complex coupling configurations. Here, we study the synchronization between violin players in complex networks with full and accurate control over the network connectivity, coupling strength, and delay. We show that the players can tune their playing period and delete connections by ignoring frustrating signals, to find a stable solution. These additional degrees of freedom enable new strategies and yield better solutions than are possible within current models such as the Kuramoto model. Our results may influence numerous fields, including traffic management, epidemic control, and stock market dynamics.

  • Anti-Zeno quantum advantage in fast-driven heat machines

    Mukherjee V., Kofman A. G. & Kurizki G. (2020) Communications Physics.
    Developing quantum machines which can outperform their classical counterparts, thereby achieving quantum supremacy or quantum advantage, is a major aim of the current research on quantum thermodynamics and quantum technologies. Here, we show that a fast-modulated cyclic quantum heat machine operating in the non-Markovian regime can lead to significant heat current and power boosts induced by the anti-Zeno effect. Such boosts signify a quantum advantage over almost all heat machines proposed thus far that operate in the conventional Markovian regime, where the quantumness of the system-bath interaction plays no role. The present effect owes its origin to the time-energy uncertainty relation in quantum mechanics, which may result in enhanced system-bath energy exchange for modulation periods shorter than the bath correlation-time.

  • Minimal quantum heat manager boosted by bath spectral filtering

    Naseem M. T., Misra A., Müstecaplıoğlu Ö. E. & Kurizki G. (2020) Physical Review Research.
    We reveal the potentially important role of a general mechanism in quantum heat management schemes, namely, spectral filtering of the coupling between the heat baths in the setup and the quantum system that controls the heat flow. Such filtering is enabled by interfaces between the system and the baths by means of harmonic-oscillator modes whose resonant frequencies and coupling strengths are used as control parameters of the system-bath coupling spectra. We show that this uniquely quantum-electrodynamic mechanism, here dubbed bath spectral filtering, boosts the performance of a minimal quantum heat manager comprised of two interacting qubits or an analogous optomechanical system, allowing this device to attain either perfect heat diode action or strongly enhanced heat transistor action.

  • Precision Limits of Tissue Microstructure Characterization by Magnetic Resonance Imaging

    Zwick A., Suter D., Kurizki G. & Alvarez G. A. (2020) Physical Review Applied.
    Characterization of microstructures in living tissues is one of the keys to diagnosing early stages of pathology and understanding disease mechanisms. However, the extraction of reliable information on biomarkers based on microstructure details is still a challenge, as the size of features that can be resolved with noninvasive magnetic resonance imaging (MRI) is orders of magnitude larger than the relevant structures. Here we derive from quantum information theory the ultimate precision limits for obtaining such details by MRI probing of water-molecule diffusion. We show that currently available MRI pulse sequences can be optimized to attain the ultimate precision limits by choosing control parameters that are uniquely determined by the expected size, the diffusion coefficient, and the spin relaxation time T-2. By attaining the ultimate precision limit per measurement, the number of measurements and the total acquisition time may be drastically reduced compared to the present state of the art. These results are expected to open alternative avenues towards unraveling diagnostic information by quantitative MRI.

  • Exact mapping between a laser network loss rate and the classical XY Hamiltonian by laser loss control

    Gershenzon I., Arwas G., Gadasi S., Tradonsky C., Friesem A., Raz O. & Davidson N. (2020) Nanophotonics.
    Recently, there has been growing interest in the utilization of physical systems as heuristic optimizers for classical spin Hamiltonians. A prominent approach employs gain-dissipative optical oscillator networks for this purpose. Unfortunately, these systems inherently suffer from an inexact mapping between the oscillator network loss rate and the spin Hamiltonian due to additional degrees of freedom present in the system such as oscillation amplitude. In this work, we theoretically analyze and experimentally demonstrate a scheme for the alleviation of this difficulty. The scheme involves control over the laser oscillator amplitude through modification of individual laser oscillator loss. We demonstrate this approach in a laser network classical XY model simulator based on a digital degenerate cavity laser. We prove that for each XY model energy minimum there corresponds a unique set of laser loss values that leads to a network state with identical oscillation amplitudes and to phase values that coincide with the XY model minimum. We experimentally demonstrate an eight fold improvement in the deviation from the minimal XY energy by employing our proposed solution scheme.

  • Mission Invisible: A Novel About the Science of Light

    Leonhardt U. (2020) .
    Invisibility has fascinated people since time immemorial, but only a decade ago did invisibility become a serious subject of scientific investigation. This lively novel, authored by an expert in the field, takes the reader on a journey to fascinating places and - en passant - on an intellectual adventure involving some of the most fascinating subjects of optics. While enjoying the fun and action of a travel story, the reader will gain an accurate notion of the real science of invisibility, of the light and shade of the business of science, as well as glimpses into different cultures. From the first page, you will gradually become immersed in a different world, the world of the science of light. The book includes an appendix providing interested readers with deeper insights into the fundamental physics of space-time, gravity and light.

  • Quantum optomechanics of a two-dimensional atomic array

    Shahmoon E., Lukin M. D. & Yelin S. F. (2020) Physical Review A.
    We demonstrate that a two-dimensional atomic array can be used as a platform for quantum optomechanics. Such arrays feature both nearly perfect reflectivity and ultralight mass, leading to significantly enhanced optomechanical phenomena. Considering the collective atom-array motion under continuous laser illumination, we study the nonlinear optical response of the array. We find that the spectrum of light scattered by the array develops multiple sidebands, corresponding to collective mechanical resonances, and exhibits nearly perfect quantum-noise squeezing. Possible extensions and applications for quantum nonlinear optomechanics are discussed.

  • Quantum Simulations with Complex Geometries and Synthetic Gauge Fields in a Trapped Ion Chain

    Manovitz T., Shapira Y., Akerman N., Stern A. & Ozeri R. (2020) PRX Quantum.
    In recent years, arrays of atomic ions in a linear radio-frequency trap have proven to be a particularly successful platform for quantum simulation. However, a wide range of quantum models and phenomena have, so far, remained beyond the reach of such simulators. In this work we introduce a technique that can substantially extend this reach using an external field gradient along the ion chain and a global, uniform driving field. The technique can be used to generate both static and time-varying synthetic gauge fields in a linear chain of trapped ions, and enables continuous simulation of a variety of coupling geometries and topologies, including periodic boundary conditions and high-dimensional Hamiltonians. We describe the technique, derive the corresponding effective Hamiltonian, propose a number of variations, and discuss the possibility of scaling to quantum-advantage-sized simulators. Additionally, we suggest several possible implementations and briefly examine two: the Aharonov-Bohm ring and the frustrated triangular ladder.

  • Attosecond spectral singularities in solid-state high-harmonic generation

    Uzan A. J., Orenstein G., Jimenez-Galan A., McDonald C., Silva R. E. F., Bruner B. D., Klimkin N. D., Blanchet V., Arusi-Parpar T., Krueger M., Rubtsov A. N., Smirnova O., Ivanov M., Yan B., Brabec T. & Dudovich N. (2020) Nature Photonics.
    Strong-field-driven electric currents in condensed-matter systems are opening new frontiers in petahertz electronics. In this regime, new challenges are arising as the roles of band structure and coherent electron-hole dynamics have yet to be resolved. Here, by using high-harmonic generation spectroscopy, we reveal the underlying attosecond dynamics that dictates the temporal evolution of carriers in multi-band solid-state systems. We demonstrate that when the electron-hole relative velocity approaches zero, enhanced constructive interference leads to the appearance of spectral caustics in the high-harmonic generation spectrum. We introduce the role of the dynamical joint density of states and identify its mapping into the spectrum, which exhibits singularities at the spectral caustics. By studying these singularities, we probe the structure of multiple unpopulated high conduction bands.

  • CdSe/CdS/CdTe Core/Barrier/Crown Nanoplatelets: Synthesis, Optoelectronic Properties, and Multiphoton Fluorescence Upconversion

    Khan A. H., Bertrand G. H. V., Teitelboim A., Sekhar M C., Polovitsyn A., Brescia R., Planelles J., Climente J. I., Oron D. & Moreels I. (2020) ACS Nano.
    Colloidal two-dimensional (2D) nanoplatelet heterostructures are particularly interesting as they combine strong confinement of excitons in 2D materials with a wide range of possible semiconductor junctions due to a template-free, solution-based growth. Here, we present the synthesis of a ternary 2D architecture consisting of a core of CdSe, laterally encapsulated by a type-I barrier of CdS, and finally a type-II outer layer of CdTe as so-called crown. The CdS acts as a tunneling barrier between CdSe- and CdTe-localized hole states, and through strain at the CdS/CdTe interface, it can induce a shallow electron barrier for CdTe-localized electrons as well. Consequently, next to an extended fluorescence lifetime, the barrier also yields emission from CdSe and CdTe direct transitions. The core/barrier/crown configuration further enables two-photon fluorescence upconversion and, due to a high nonlinear absorption cross section, even allows to upconvert three near-infrared photons into a single green photon. These results demonstrate the capability of 2D heterostructured nanoplatelets to combine weak and strong confinement regimes to engineer their optoelectronic properties.

  • Observation of persistent orientation of chiral molecules by a laser field with twisted polarization

    Tutunnikov I., Floss J., Gershnabel E., Brumer P., Averbukh I. S., Milner A. A. & Milner V. (2020) Physical Review A.
    Molecular chirality is an omnipresent phenomenon of fundamental significance in physics, chemistry, and biology. For this reason, the search for various techniques for enantioselective control, detection, and separation of chiral molecules is of particular importance. It has been recently predicted that laser fields with twisted polarization may induce a persistent enantioselective field-free orientation of chiral molecules. Here, we report an experimental observation of this phenomenon using propylene oxide molecules (CH3CHCH2O, or PPO) spun by an optical centrifuge-a laser pulse-whose linear polarization undergoes an accelerated rotation around its propagation direction. We show that PPO molecules remain oriented on a timescale exceeding the duration of the centrifuge pulse by several orders of magnitude. The demonstrated long-time field-free enantioselective orientation may open new avenues for optical manipulation, discrimination, and, potentially, the separation of molecular enantiomers.

  • Transverse drag of slow light in moving atomic vapor

    Solomons Y., Banerjee C., Smartsev S., Friedman J., Eger D., Firstenberg O. & Davidson N. (2020) Optics Letters.
    The Fresnel-Fizeau effect of transverse drag, in which the trajectory of a light beam changes due to transverse motion of the optical medium, is usually extremely small and hard to detect. We observe transverse drag in a moving hot-vapor cell, utilizing slow light due to electromagnetically induced transparency (EIT). The drag effect is enhanced by a factor 400,000, corresponding to the ratio between the light speed in vacuum and the group velocity under the EIT conditions. We study the contribution of the thermal atomic motion, which is much faster than the mean medium velocity, and identify the regime where its effect on the transverse drag is negligible.

  • Single beam low frequency 2D Raman spectroscopy

    Hurwitz I., Raanan D., Ren L., Frostig H., Oulevey P., Bruner B. D., Dudovich N. & Silberberg Y. (2020) Optics Express.
    Low frequency Raman spectroscopy resolves the slow vibrations resulting from collective motions of molecular structures. This frequency region is extremely challenging to access via other multidimensional methods such as 2D-IR. In this paper, we describe a new scheme which measures 2D Raman spectra in the low frequency regime. We separate the pulse into a spectrally shaped pump and a transform-limited probe, which can be distinguished by their polarization states. Low frequency 2D Raman spectra in liquid tetrabromoethane are presented, revealing coupling dynamics at frequencies as low as 115 cm−1. The experimental results are supported by numerical simulations which replicate the key features of the measurement. This method opens the door for the deeper exploration of vibrational energy surfaces in complex molecular structures.

  • Chiral and SHG-Active Metal-Organic Frameworks Formed in Solution and on Surfaces: Uniformity, Morphology Control, Oriented Growth, and Post-assembly Functionalization

    Wen Q., Tenenholtz S., Shimon L. J. W., Bar-Elli O., Beck L., Houben L., Cohen S. R., Feldman Y., Oron D., Lahav M. & van der Boom M. E. (2020) Journal of the American Chemical Society.
    We demonstrate the formation of uniform and oriented metal-organic frameworks using a combination of anion-effects and surface-chemistry. Subtle but significant morphological changes result from the nature of the coordinative counter-anion of the following metal salts: NiX2 with (X = Br-, Cl-, NO3-, and OAc-). Crystals could be obtained in solution or by template surface growth. The latter resulting in truncated crystals that resemble a half-structure of the solution-grown ones. The oriented surface-bound metal-organic frameworks (sMOFs) are obtained via a one-step solvothermal approach, rather than in a layer-by-layer approach. The MOFs are grown on Si/SiOx substrates modified with an organic monolayer or on glass substrates covered with a transparent conductive oxide (TCO). Regardless of the different morphologies, the crystallographic packing is nearly identical and is not affected by the type of anion, nor by solution versus the surface chemistry. A propeller-type arrangement of the non-chiral ligands around the metal center affords a chiral structure with two geometrically different helical channels in a 2:1 ratio with the same handedness. To demonstrate the accessibility and porosity of the macroscopically-oriented channels, a chromophore (resorufin sodium salt) was successfully embedded into the channels of the crystals by diffusion from solution, resulting in fluorescent crystals. These "colored" crystals displayed polarized emission (red) with a high polarization ratio because of the alignment of these dyes imposed by the crystallographic structure. A second-harmonic generation (SHG) study revealed Kleinman-symmetry forbidden non-linear optical properties. These surface-bound and oriented SHG-active MOFs have the potential for use as single non-linear optical (NLO) devices.

  • Rotation sensing with improved stability using point-source atom interferometry

    Avinadav C., Yankelev D., Shuker M., Davidson N. & Firstenberg O. (2020) Physical Review A.
    Point-source atom interferometry is a promising approach for implementing robust, high-sensitivity, rotation sensors using cold atoms. However, its scale factor, i.e., the ratio between the interferometer signal and the actual rotation rate, depends on the initial conditions of the atomic cloud, which may drift in time and result in bias instability, particularly in compact devices with short interrogation times. We present two methods to stabilize the scale factor. One relies on a model-based correction which exploits correlations between multiple features of the interferometer output and works on a single-shot basis. The other is a self-calibrating method where a known bias rotation is applied to every other measurement, requiring no prior knowledge of the underlying model but reducing the sensor bandwidth by a factor of two. We demonstrate both schemes experimentally with complete suppression of scale-factor drifts, maintaining the original rotation sensitivity and allowing for bias-free operation over several hours.

  • Optimal control of an optical quantum memory based on noble-gas spins

    Katz O., Shaham R., Reches E., Gorshkov A. V. & Firstenberg O. (2020) arXiv.
    In Ref. [Katz et al., arXiv:2007.08770 (2020)], we present a mechanism and optimal procedures for mapping the quantum state of photons onto an optically inaccessible macroscopic state of noble-gas spins, which functions as a quantum memory. Here we introduce and analyze a detailed model of the memory operation. We derive the equations of motion for storage and retrieval of non-classical light and design optimal control strategies. The detailed model accounts for quantum noise and for thermal atomic motion, including the effects of optical mode structure and imperfect anti-relaxation wall coating. We conclude with proposals of practical experimental configurations of the memory, with lifetimes ranging from seconds to hours.

  • Experimental demonstration of crowd synchrony and first-order transition with lasers

    Mahler S., Friesem A. A. & Davidson N. (2020) Physical Review Research.
    Synchronization of different and independent oscillators that interact with each other via a common intermediate is ubiquitous in many fields. Here, we experimentally demonstrate the effect of crowd synchrony, analogous to that of the Millennium Bridge, by resorting to coupled lasers. When the number of lasers is below a critical number, there is no synchronization, but after reaching the critical number, the lasers instantaneously synchronize. We show that the synchronization of the lasers as a function of their number follows a first-order transition, and that our experimental results are in good agreement with those predicted by theoretical models.

  • Three-dimensional sensing of arbitrarily shaped nanoparticles by whispering gallery mode resonators

    Guendelman G., Lovsky Y., Yacoby E., Mor O. E., Kaplan-Ashiri I., Goldbart O. & Dayan B. (2020) Optics Express.
    Whispering-gallery-mode (WGM) microresonators are a promising platform for highly sensitive, label-free detection and probing of individual nano-objects. Our work expands these capabilities by providing the analysis tools required for three-dimensional (3D) characterization of arbitrarily shaped nanoparticles. Specifically, we introduce a theoretical model that describes interactions between nanoparticles and WGM resonators, taking into account effects that were often not considered, such as the elliptical polarization of the transverse-magnetic (TM) mode, the possible non-spherical shape of the nanoparticle, its finite size, and the open-system nature of the modes. We also introduce a self referencing measurement method that allows the extraction of information from measurements done at arbitrary positions of the nanoparticles within the WGM. We verify our model by experimentally probing a single Tungsten-disulfide (WS2) nanotube with a silica microtoroid resonator inside a scanning electron-microscope (SEM) and perform 3D characterization of the nanotube.

  • Spin-Phonon Interfaces in Coupled Nanomechanical Cantilevers

    Oeckinghaus T., Momenzadeh S. A., Scheiger P., Shalomayeya T., Finkler A., Dasari D., Stoehr R. & Wrachtrup J. (2020) Nano Letters.
    Coupled micro- and nanomechanical oscillators are of fundamental and technical interest for emerging quantum technologies. Upon interfacing with long-lived solid-state spins, the coherent manipulation of the quantum hybrid system becomes possible even at ambient conditions. Although the ability of these systems to act as a quantum bus inducing long-range spin-spin interactions has been known, the possibility to coherently couple electron/nuclear spins to the common modes of multiple oscillators and map their mechanical motion to spin-polarization has not been experimentally demonstrated. We here report experiments on interfacing spins to the common modes of a coupled cantilever system and show their correlation by translating ultralow forces induced by radiation from one oscillator to a distant spin. Further, we analyze the coherent spin-spin coupling induced by the common modes and estimate the entanglement generation among distant spins.

  • Deviations from generalized equipartition in confined, laser-cooled atoms

    Afek G., Cheplev A., Courvoisier A. & Davidson N. (2020) Physical Review A.
    We observe a significant steady-state deviation from the generalized equipartition theorem, one of the pivotal results of classical statistical mechanics, in a system of confined, laser-cooled atoms. We parametrize this deviation, measure its dynamics, and show that its steady-state value quantifies the departure of nonthermal states from thermal equilibrium even for anharmonic confinement. In particular, we find that deviations from equipartition grow as the system dynamics becomes more anomalous. We present numerical simulations that validate the experimental data and reveal an inhomogeneous distribution of the kinetic energy through the system, supported by an analytical examination of the phase space.

  • Efficient ion-photon qubit SWAP gate in realistic ion cavity-QED systems without strong coupling

    Borne A., Northup T. E., Blatt R. & Dayan B. (2020) Optics Express.
    We present a scheme for deterministic ion-photon qubit exchange, namely a SWAP gate, based on realistic cavity-QED systems with <sup>171</sup>Yb <sup>+</sup> <sup>40</sup>Ca <sup>+</sup> and <sup>138</sup>Ba <sup>+</sup> ions. The gate can also serve as a single-photon quantum memory, in which an outgoing photon heralds the successful arrival of the incoming photonic qubit. Although strong coupling, namely having the single-photon Rabi frequency be the fastest rate in the system, is often assumed essential, this gate (similarly to the Duan-Kimble C-phase gate) requires only Purcell enhancement, i.e. high single-atom cooperativity. Accordingly, it does not require small mode volume cavities, which are challenging to incorporate with ions due to the difficulty of trapping them close to dielectric surfaces. Instead, larger cavities, potentially more compatible with the trap apparatus, are sufficient, as long as their numerical aperture is high enough to maintain small mode area at the ion's position. We define the optimal parameters for the gate's operation and simulate the expected fidelities and efficiencies, demonstrating that efficient photon-ion qubit exchange, a valuable building block for scalable quantum computation, is practically attainable with current experimental capabilities.

  • Combining experiments and relativistic theory for establishing accurate radiative quantities in atoms: The lifetime of the 2P3/2 state in Ca40+

    Meir Z., Sinhal M., Safronova M. S. & Willitsch S. (2020) Physical review. A.
    We report a precise determination of the lifetime of the (4p)2P3/2 state of 40Ca+, τP3/2=6.639(42)ns, using a combination of measurements of the induced light shift and scattering rate on a single trapped ion. Good agreement with the result of a recent high-level theoretical calculation, 6.69(6) ns [M. S. Safronova et al., Phys. Rev. A 83, 012503 (2011)], but a 6-σ discrepancy with the most precise previous experimental value, 6.924(19) ns [J. Jin et al., Phys. Rev. Lett. 70, 3213 (1993)], is found. To corroborate the consistency and accuracy of the new measurements, relativistically corrected ratios of reduced-dipole-matrix elements are used to directly compare our result with a recent result for the P1/2 state, yielding a good agreement. The application of the present method to precise determinations of radiative quantities of molecular systems is discussed.

  • Device-independent Randomness Amplification and Privatization

    Kessler M. & Arnon-Friedman R. (2020) IEEE Journal on Selected Areas in Information Theory.
    Secret and perfect randomness is an essential resource in cryptography. Yet, it is not even clear that such exists. It is well known that the tools of classical computer science do not allow us to create secret and perfect randomness from a single weak public source. Quantum physics, on the other hand, allows for such a process, even in the most paranoid cryptographic sense termed “device-independent quantum cryptography”. We propose and prove the security of a new device-independent protocol that takes any single public Santha-Vazirani source as input and creates a secret close to uniform string in the presence of a quantum adversary. Our work is the first to achieve randomness amplification with all the following properties: (1) amplification and “privatization” of a public Santha-Vazirani source with arbitrary bias (2) the use of a device with only two components (3) non-vanishing extraction rate and (4) maximal noise tolerance. In particular, this implies that our protocol is the first protocol that can possibly be implemented with reachable parameters. We achieve these by combining three new tools: a particular family of Bell inequalities, a proof technique to lower bound entropy in the device-independent setting, and a framework for quantum-proof multi-source extractors.

  • Effects of the Transverse Instability and Wave Breaking on the Laser-Driven Thin Foil Acceleration

    Wan Y., Andriyash I. A., Lu W., Mori W. B. & Malka V. A. (2020) Physical Review Letters.
    Acceleration of ultrathin foils by the laser radiation pressure promises a compact alternative to the conventional ion sources. Among the challenges on the way to practical realization, one fundamental is a strong transverse plasma instability, which develops density perturbations and breaks the acceleration. In this Letter, we develop a theoretical model supported by three-dimensional numerical simulations to explain the transverse instability growth from noise to wave breaking and its crucial effect on stopping the acceleration. The wave-broken nonlinear mode triggers rapid stochastic heating that finally explodes the target. Possible paths to mitigate this problem for getting efficient ion acceleration are discussed.

  • Echo in a single vibrationally excited molecule

    Qiang J., Tutunnikov I., Lu P., Lin K., Zhang W., Sun F., Silberberg Y., Prior Y., Averbukh I. S. & Wu J. (2020) Nature Physics.
    Echoes occur in many physical systems, typically in inhomogeneously broadened ensembles of nonlinear objects. They are often used to eliminate the effects of dephasing caused by interactions with the environment as well as to enable the observation of proper, inherent object properties. Here, we report the experimental observation of quantum wave-packet echoes in a single, isolated molecule. The entire dephasing-rephasing cycle occurs without any inhomogeneous spread of molecular properties, or any interaction with the environment, and offers a way to probe the internal coherent dynamics of single molecules. In our experiments, we impulsively excite a vibrational wave packet in an anharmonic molecular potential and observe its oscillations and eventual dispersion with time. A second, delayed pulse gives rise to an echo-a partial recovery of the initial coherent oscillations. The vibrational dynamics of single molecules is visualized by a time-delayed probe pulse dissociating them, one at a time. Two mechanisms for the echo formation are discussed: a.c. Stark-induced molecular potential shaking and creation of a depletion-induced 'hole' in the nuclear spatial distribution. The single-molecule wave-packet echoes may lead to the development of new tools for probing ultrafast intramolecular processes in various molecules.Following an impulsive laser excitation of a single molecule, a dispersed vibrational wave-packet is partially rephased by a second pulse, and a wave-packet echo is observed. This wave-packet echo probes ultrafast intramolecular processes in the isolated molecule.

  • Attosecond spectral singularities in solid-state high-harmonic generation

    Uzan A. J., Orenstein G., Bruner B. D., Jimenez-Galan Á., McDonald C., Silva R. E., Klimkin N. D., Blanchet V., Arusi-Parpar T., Krüger M., Rubtsov A. N., Smirnova O., Ivanov M., Yan B., Brabec T. & Dudovich N. (2020) .
    Using high-harmonic generation spectroscopy, we reveal the underlying attosecond dynamics in multi-band solid-state systems. We identify the mapping of spectral caustics into the high-harmonic spectrum, and probe the structure of multiple unpopulated high conduction bands.

  • Spatiotemporal rotational dynamics of laser-driven molecules

    Lin K., Tutunnikov I., Ma J., Qiang J., Zhou L., Faucher O., Prior Y., Averbukh I. S. & Wu J. (2020) Advanced Photonics.
    Molecular alignment and orientation by laser fields has attracted significant attention in recent years, mostly due to new capabilities to manipulate the molecular spatial arrangement. Molecules can now be efficiently prepared for ionization, structural imaging, orbital tomography, and more, enabling, for example, shooting of dynamic molecular movies. Furthermore, molecular alignment and orientation processes give rise to fundamental quantum and classical phenomena like quantum revivals, Anderson localization, and rotational echoes, just to mention a few. We review recent progress on the visualization, coherent control, and applications of the rich dynamics of molecular rotational wave packets driven by laser pulses of various intensities, durations, and polarizations. In particular, we focus on the molecular unidirectional rotation and its visualization, the orientation of chiral molecules, and the three-dimensional orientation of asymmetric-top molecules. Rotational echoes are discussed as an example of nontrivial dynamics and detection of prepared molecular states.

  • Enhanced laser-driven proton acceleration with gas–foil targets

    Levy D., Davoine X., Debayle A., Gremillet L. & Malka V. (2020) Journal of Plasma Physics.
    We study numerically the mechanisms of proton acceleration in gas–foil targets driven by an ultraintense femtosecond laser pulse. The target consists of a near-critical-density hydrogen gas layer of a few tens of microns attached to a 2 μ m-thick solid carbon foil with a contaminant thin proton layer at its back side. Two-dimensional particle-in-cell simulations show that, at optimal gas density, the maximum energy of the contaminant protons is increased by a factor of ∼ 4 compared with a single foil target. This improvement originates from the near-complete laser absorption into relativistic electrons in the gas. Several energetic electron populations are identified, and their respective effect on the proton acceleration is quantified by computing the electrostatic fields that they generate at the protons’ positions. While each of those electron groups is found to contribute substantially to the overall accelerating field, the dominant one is the relativistic thermal bulk that results from the nonlinear wakefield excited in the gas, as analysed recently by Debayle et al. (New J. Phys., vol. 19, 2017, 123013). Our analysis also reveals the important role of the neighbouring ions in the acceleration of the fastest protons, and the onset of multidimensional effects caused by the time-increasing curvature of the proton layer.

  • Solitons supported by intensity-dependent dispersion

    Lin C., Chang J., Kurizki G. & Lee R. (2020) Optics Letters.
    Soliton solutions are studied for paraxial wave propagation with intensity-dependent dispersion. Although the corresponding Lagrangian density has a singularity, analytical solutions, derived by the pseudo-potential method and the corresponding phase diagram, exhibit one- and two-humped solitons with almost perfect agreement to numerical solutions. The results obtained in this work reveal a hitherto unexplored area of soliton physics associated with nonlinear corrections to wave dispersion. (C) 2020 Optical Society of America

  • Optical Imaging of Coherent Molecular Rotors

    Bert J., Prost E., Tutunnikov I., Béjot P., Hertz E., Billard F., Lavorel B., Steinitz U., Averbukh I. S. & Faucher O. (2020) Laser and Photonics Reviews.
    Short laser pulses are widely used for controlling molecular rotational degrees of freedom and inducing molecular alignment, orientation, unidirectional rotation, and other types of coherent rotational motion. To follow the ultrafast rotational dynamics in real time, several techniques for producing molecular movies have been proposed based on the Coulomb explosion of rotating molecules, or recovering molecular orientation from the angular distribution of high harmonics. The present work offers and demonstrates a novel nondestructive optical method for direct visualization and recording of movies of coherent rotational dynamics in a molecular gas. The technique is based on imaging the time-dependent polarization dynamics of a probe light propagating through a gas of coherently rotating molecules. The probe pulse continues through a radial polarizer, and is then recorded by a camera. The technique is illustrated by implementing it with two examples of time-resolved rotational dynamics: alignment–antialignment cycles in a molecular gas excited by a single linearly polarized laser pulse, and unidirectional molecular rotation induced by a pulse with twisted polarization. This method may open new avenues in studies on fast chemical transformation phenomena and ultrafast molecular dynamics caused by strong laser fields of various complexities.

  • Readout and control of an endofullerene electronic spin

    Pinto D., Paone D., Kern B., Dierker T., Wieczorek R., Singha A., Dasari D., Finkler A., Harneit W., Wrachtrup J. & Kern K. (2020) Nature Communications.
    Atomic spins for quantum technologies need to be individually addressed and positioned with nanoscale precision. C<sub>60</sub> fullerene cages offer a robust packaging for atomic spins, while allowing in-situ physical positioning at the nanoscale. However, achieving single-spin level readout and control of endofullerenes has so far remained elusive. In this work, we demonstrate electron paramagnetic resonance on an encapsulated nitrogen spin (<sup>14</sup>N@C<sub>60</sub>) within a C<sub>60</sub> matrix using a single near-surface nitrogen vacancy (NV) center in diamond at 4.7 K. Exploiting the strong magnetic dipolar interaction between the NV and endofullerene electronic spins, we demonstrate radio-frequency pulse controlled Rabi oscillations and measure spin-echos on an encapsulated spin. Modeling the results using second-order perturbation theory reveals an enhanced hyperfine interaction and zero-field splitting, possibly caused by surface adsorption on diamond. These results demonstrate the first step towards controlling single endofullerenes, and possibly building large-scale endofullerene quantum machines, which can be scaled using standard positioning or self-assembly methods.

  • From megahertz to terahertz qubits encoded in molecular ions: theoretical analysis of dipole-forbidden spectroscopic transitions in N2+

    Najafian K., Meir Z. & Willitsch S. (2020) Physical chemistry chemical physics : PCCP.
    Recent advances in quantum technologies have enabled the precise control of single trapped molecules on the quantum level. Exploring the scope of these new technologies, we studied theoretically the implementation of qubits and clock transitions in the spin, rotational, and vibrational degrees of freedom of molecular nitrogen ions including the effects of magnetic fields. The relevant spectroscopic transitions span six orders of magnitude in frequency, illustrating the versatility of the molecular spectrum for encoding quantum information. We identified two types of magnetically insensitive qubits with very low ("stretched"-state qubits) or even zero ("magic" magnetic-field qubits) linear Zeeman shifts. The corresponding spectroscopic transitions are predicted to shift by as little as a few mHz for an amplitude of magnetic-field fluctuations on the order of a few mG, translating into Zeeman-limited coherence times of tens of minutes encoded in the rotations and vibrations of the molecule. We also found that the Q(0) line of the fundamental vibrational transition is magnetic-dipole allowed by interaction with the first excited electronic state of the molecule. The Q(0) transitions, which benefit from small systematic shifts for clock operation and is thus well suited for testing a possible variation in the proton-to-electron mass ratio, were so far not considered in single-photon spectra. Finally, we explored possibilities to coherently control the nuclear-spin configuration of N2+ through the magnetically enhanced mixing of nuclear-spin states.Theoretical study of the implementation of qubits and clock transitions in the spin, rotational, and vibrational degrees of freedom of molecular nitrogen ions including the effect of magnetic fields.

  • Improved Phase Locking of Laser Arrays with Nonlinear Coupling

    Mahler S., Goh M. L., Tradonsky C., Friesem A. A. & Davidson N. (2020) Physical Review Letters.
    An arrangement based on a degenerate cavity laser for forming an array of nonlinearly coupled lasers with an intracavity saturable absorber is presented. More than 30 lasers were spatially phase locked and temporally Q switched. The arrangement with nonlinear coupling was found to be 25 times more sensitive to loss differences and converged five times faster to the lowest loss phase locked state than with linear coupling, thus providing a unique solution to problems that have several near-degenerate solutions.

  • Phase-locked laser-wakefield electron acceleration

    Caizergues C., Smartsev S., Malka V. & Thaury C. (2020) Nature Photonics.
    Subluminal and superluminal light pulses have attracted considerable attention in recent decades(1-4), opening perspectives in telecommunications, optical storage and fundamental physics(5). Usually achieved in matter, superluminal propagation has also been demonstrated in vacuum with quasi-Bessel beams(6,7)or spatio-temporal couplings(8,9). Although, in the first case, the propagation was diffraction free, but with hardly controllable pulse velocities and limited to moderate intensities, in the second, high tunability was achieved, but with substantially lengthened pulse durations. Here we report a new concept that extends these approaches to relativistic intensities and ultrashort pulses by mixing spatio-temporal couplings and quasi-Bessel beams to independently control the light velocity and intensity. When used to drive a laser-plasma accelerator(10), this concept leads to a new regime that is dephasing free, where the electron beam energy gain increases by more than one order of magnitude.

  • On the Stark Effect of the O I 777-nm Triplet in Plasma and Laser Fields

    Stambulchik E., Kroupp E., Maron Y. & Malka V. (2020) Atoms.
    The O I 777-nm triplet transition is often used for plasma density diagnostics. It is also employed in nonlinear optics setups for producing quasi-comb structures when pumped by a near-resonant laser field. Here, we apply computer simulations to situations of the radiating atom subjected to the plasma microfields, laser fields, and both perturbations together. Our results, in particular, resolve a controversy related to the spectral line anomalously broadened in some laser-produced plasmas. The importance of using time-dependent density matrix is discussed.

  • Long-Lasting Molecular Orientation Induced by a Single Terahertz Pulse

    Xu L., Tutunnikov I., Gershnabel E., Prior Y. & Averbukh I. S. (2020) Physical Review Letters.
    We present a novel, previously unreported phenomenon appearing in a thermal gas of nonlinear polar molecules excited by a single THz pulse. We find that the induced orientation lasts long after the excitation pulse is over. In the case of symmetric-top molecules, the time-averaged orientation remains indefinitely constant, whereas in the case of asymmetric-top molecules the orientation persists for a long time after the end of the pulse. We discuss the underlying mechanism, study its nonmonotonous temperature and amplitude dependencies, and show that there exist optimal parameters for maximal residual orientation. The persistent orientation implies a long-lasting macroscopic dipole moment, which may be probed by even harmonic generation and may enable deflection by inhomogeneous electrostatic fields.

  • Pulsed-pump phosphorus-doped fiber Raman amplifier around 1260 nm for applications in quantum non-linear optics

    Poem E., Golenchenko A., Davidson O., Arenfrid O., Finkelstein R. & Firstenberg O. (2020) Optics Express.
    We describe a fiber Raman amplifier for nanosecond and sub-nanosecond pulses centered around 1260 nm. The amplification takes place inside a 4.5-m-long polarizationmaintaining phosphorus-doped fiber, pumped at 1080 nm by 3-ns-long pulses with a repetition rate of 200 kHz and up to 1.75 kWpeak power. The input seed pulses are of sub-mW peak-power and minimal duration of 0.25 ns, carved out of a continuous-wave laser with sub-MHz linewidth. We obtain linearly polarized output pulses with peak powers of up to 1.4 kW, corresponding to peak-power conversion efficiency of over 80%. An ultrahigh small signal gain of 90 dB is achieved, and the signal-to-noise ratio 3 dB below the saturation power is above 20 dB. No significant temporal and spectral broadening is observed for output pulses up to 400 W peak power, and broadening at higher powers can be reduced by phase modulation of the seed pulse. Thus, nearly-transform-limited pulses with peak power up to 1 kW are obtained. Finally, we demonstrate the generation of pulses with controllable frequency chirp, pulses with variable width, and double pulses. This amplifier is thus suitable for coherent control of narrow atomic resonances, especially for the fast and coherent excitation of rubidium atoms to Rydberg states. These abilities open the way towards several important applications in quantum non-linear optics.

  • Erratum to: EuPRAXIA Conceptual Design Report: Eur. Phys. J. Special Topics 229, 3675-4284 (2020), https://doi.org/10.1140/epjst/e2020-000127-8

    Assmann R. W., Weikum M. K., Akhter T., Alesini D., Alexandrova A. S., Anania M. P., Andreev N. E., Andriyash I., Artioli M., Aschikhin A., Audet T., Bacci A., Barna I. F., Bartocci S., Bayramian A., Beaton A., Beck A., Bellaveglia M., Beluze A., Bernhard A., Biagioni A., Bielawski S., Bisesto F. G., Bonatto A., Boulton L., Brandi F., Brinkmann R., Briquez F., Brottier F., Bründermann E., Büscher M., Buonomo B., Bussmann M. H., Bussolino G., Campana P., Cantarella S., Cassou K., Chancé A., Chen M., Chiadroni E., Cianchi A., Cioeta F., Clarke J. A., Cole J. M., Costa G., Couprie M. -., Cowley J., Croia M., Cros B., Crump P. A., D’Arcy R., Dattoli G., Del Dotto A., Delerue N., Del Franco M., Delinikolas P., De Nicola S., Dias J. M., Di Giovenale D., Diomede M., Di Pasquale E., Di Pirro G., Di Raddo G., Dorda U., Erlandson A. C., Ertel K., Esposito A., Falcoz F., Falone A., Fedele R., Ferran Pousa A., Ferrario M., Filippi F., Fils J., Fiore G., Fiorito R., Fonseca R. A., Franzini G., Galimberti M., Gallo A., Galvin T. C., Ghaith A., Ghigo A., Giove D., Giribono A., Gizzi L. A., Grüner F. J., Habib A. F., Haefner C., Heinemann T., Helm A., Hidding B., Holzer B. J., Hooker S. M., Hosokai T., Hübner M., Ibison M., Incremona S., Irman A., Iungo F., Jafarinia F. J., Jakobsson O., Jaroszynski D. A., Jaster-Merz S., Joshi C., Kaluza M., Kando M., Karger O. S., Karsch S., Khazanov E., Khikhlukha D., Kirchen M., Kirwan G., Kitégi C., Knetsch A., Kocon D., Koester P., Kononenko O. S., Korn G., Kostyukov I., Kruchinin K. O., Labate L., Le Blanc C., Lechner C., Lee P., Leemans W., Lehrach A., Li X., Li Y., Libov V., Lifschitz A., Lindstrøm C. A., Litvinenko V., Lu W., Lundh O., Maier A. R., Malka V., Manahan G. G., Mangles S. P. D., Marcelli A., Marchetti B., Marcouillé O., Marocchino A., Marteau F., Martinez de la Ossa A., Martins J. L., Mason P. D., Massimo F., Mathieu F., Maynard G., Mazzotta Z., Mironov S., Molodozhentsev A. Y., Morante S., Mosnier A., Mostacci A., Müller A. -., Murphy C. D., Najmudin Z., Nghiem P. A. P., Nguyen F., Niknejadi P., Nutter A., Osterhoff J., Oumbarek Espinos D., Paillard J. -., Papadopoulos D. N., Patrizi B., Pattathil R., Pellegrino L., Petralia A., Petrillo V., Piersanti L., Pocsai M. A., Poder K., Pompili R., Pribyl L., Pugacheva D., Reagan B. A., Resta-Lopez J., Ricci R., Romeo S., Rossetti Conti M., Rossi A. R., Rossmanith R., Rotundo U., Roussel E., Sabbatini L., Santangelo P., Sarri G., Schaper L., Scherkl P., Schramm U., Schroeder C. B., Scifo J., Serafini L., Sharma G., Sheng Z. M., Shpakov V., Siders C. W., Silva L. O., Silva T., Simon C., Simon-Boisson C., Sinha U., Sistrunk E., Specka A., Spinka T. M., Stecchi A., Stella A., Stellato F., Streeter M. J. V., Sutherland A., Svystun E. N., Symes D., Szwaj C., Tauscher G. E., Terzani D., Toci G., Tomassini P., Torres R., Ullmann D., Vaccarezza C., Valléau M., Vannini M., Vannozzi A., Vescovi S., Vieira J. M., Villa F., Wahlström C. -., Walczak R., Walker P. A., Wang K., Welsch A., Welsch C. P., Weng S. M., Wiggins S. M., Wolfenden J., Xia G., Yabashi M., Zhang H., Zhao Y., Zhu J. & Zigler A. (2020) The European physical journal. ST, Special topics.

  • Quantum Matrix: Henry Bar's Perilous Struggle for Quantum Coherence

    Gordon G. & Kurizki G. (2020) .
    In this book, Henry Bar, physicist and the first quantum superhero, guides the reader through the amazing quantum world. His hair-raising adventures in his perilous struggle for quantum coherence are graphically depicted by comics and thoroughly explained to the lay reader. Behind each adventure lies a key concept in quantum physics. These concepts range from the basic quantum coherence and entanglement through tunnelling and the recently discovered quantumdecoherence control, to the principles of the emerging technologies of quantum communication and computing. The explanations of the concepts are accessible, but nonetheless rigorous and detailed. They are followed by an account of the broader context of these concepts, their historic perspective, current status and forthcoming developments. Finally, thought-provoking philosophical and cultural implications of these concepts are discussed. The mathematical appendices of all chapters cover in a straightforward manner the core aspects of quantum physics at the level of a university introductory course. The Quantum Matrix presents an entertaining, popular, yet comprehensive picture of quantum physics . It can be read as a light-hearted illustrated tale, a philosophical treatise, or a textbook. Either way, the book lets the reader delve deeply into the wondrous quantum world from diverse perspectives and obtain glimpses into the quantum technologies that are about to reshape our lives. This book offers the reader an enjoyable and rewarding voyage through the quantumworld.

  • Theory of robust multiqubit nonadiabatic gates for trapped ions

    Shapira Y., Shaniv R., Manovitz T., Akerman N., Peleg L., Gazit L., Ozeri R. & Stern A. (2020) Physical Review A.
    The prevalent approach to executing quantum algorithms on quantum computers is to break down the algorithms to a concatenation of universal gates, typically single and two-qubit gates. However such a decomposition results in long gate sequences which are exponential in the qubit register size. Furthermore, gate fidelities tend to decrease when acting in larger qubit registers. Thus high-fidelity implementations in large qubit registers are still a prominent challenge. Here we propose and investigate multiqubit entangling gates for trapped ions. Our gates couple many qubits at once, allowing us to decrease the total number of gates used while retaining a high gate fidelity. Our method employs all of the normal modes of motion of the ion chain, which allows us to operate outside of the adiabatic regime and at rates comparable to the secular ion-trapping frequency. Furthermore we extend our method for generating Hamiltonians which are suitable for quantum analog simulations, such as a nearest-neighbor spin Hamiltonian or the Su-Schrieffer-Heeger Hamiltonian.

  • Path-Independent Quantum Gates with Noisy Ancilla

    Ma W., Zhang M., Wong Y., Noh K., Rosenblum S., Reinhold P., Schoelkopf R. J. & Jiang L. (2020) Physical Review Letters.
    Ancilla systems are often indispensable to universal control of a nearly isolated quantum system. However, ancilla systems are typically more vulnerable to environmental noise, which limits the performance of such ancilla-assisted quantum control. To address this challenge of ancilla-induced decoherence, we propose a general framework that integrates quantum control and quantum error correction, so that we can achieve robust quantum gates resilient to ancilla noise. We introduce the path independence criterion for fault-tolerant quantum gates against ancilla errors. As an example, a path-independent gate is provided for superconducting circuits with a hardware-efficient design.

  • Atom interferometry with thousand-fold increase in dynamic range

    Yankelev D., Avinadav C., Davidson N. & Firstenberg O. (2020) Science Advances.
    The periodicity inherent to any interferometric signal entails a fundamental trade-off between sensitivity and dynamic range of interferometry-based sensors. Here, we develop a methodology for substantially extending the dynamic range of such sensors without compromising their sensitivity, stability, and bandwidth. The scheme is based on simultaneous operation of two nearly identical interferometers, providing a moiré-like period much larger than 2π and benefiting from close-to-maximal sensitivity and from suppression of common-mode noise. The methodology is highly suited to atom interferometers, which offer record sensitivities in measuring gravito-inertial forces but suffer from limited dynamic range. We experimentally demonstrate an atom interferometer with a dynamic-range enhancement of more than an order of magnitude in a single shot and more than three orders of magnitude within a few shots for both static and dynamic signals. This approach can considerably improve the operation of interferometric sensors in challenging, uncertain, or rapidly varying conditions.

  • Spin-bath polarization via disentanglement

    Rao D. D. B., Ghosh A., Gelbwaser-Klimovsky D., Bar-Gill N. & Kurizki G. (2020) New Journal of Physics.
    The occurrence of any physical process is restricted by the constraints imposed by the laws of thermodynamics on the energy and entropy exchange involved. A prominent class of processes where thermodynamic constraints are crucial involve polarization of nuclear spin baths that are at the heart of magnetic resonance imaging, nuclear magnetic resonance (NMR), quantum information processing. Polarizing a spin bath, is the key to enhancing the sensitivity of these tools, leading to new analytical capabilities and improved medical diagnostics. In recent years, significant effort has been invested in identifying the far-reaching consequences of quantum modifications to classical thermodynamics for such processes. Here we focus on the adverse role of quantum correlations (entanglement) in the spin bath that can impede its cooling in many realistic scenarios. We propose to remove this impediment by modified cooling schemes, incorporating probe-induced disentanglement or, equivalently, alternating non-commuting probe-bath interactions to suppress the buildup of quantum correlations in the bath. The resulting bath polarization is thereby exponentially enhanced. The underlying quantum thermodynamic principles have far-reaching implications for a broad range of quantum technological applications.

  • Spatial molecular interferometry via multidimensional high-harmonic spectroscopy

    Uzan A. J., Soifer H., Pedatzur O., Clergerie A., Larroque S., Bruner B. D., Pons B., Ivanov M., Smirnova O. & Dudovich N. (2020) Nature Photonics.
    A single-molecule attosecond interferometry that can retrieve the spectral phase information associated with the structure of molecular orbitals, as well as the phase accumulated by an electron as it tunnels out, is demonstrated.Interferometry is a basic tool to resolve coherent properties in a wide range of light or matter wave phenomena. In the strong-field regime, interferometry serves as a fundamental building block in revealing ultrafast electron dynamics. In this work we manipulate strong-field-driven electron trajectories and probe the coherence of a molecular wavefunction by inducing an interferometer on a microscopic level. The two arms of the interferometer are controlled by a two-colour field, while the interference pattern is read via advanced, three-dimensional high-harmonic spectroscopy. This scheme recovers the spectral phase information associated with the structure of molecular orbitals, as well as the spatial properties of the interaction itself. Zooming into one of the most fundamental strong-field phenomena-field-induced tunnel ionization-we reconstruct the angle at which the electronic wavefunction tunnels through the barrier and follow its evolution with attosecond precision.

  • The case for a Casimir cosmology

    Leonhardt U. (2020) Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.
    The cosmological constant, also known as dark energy, was believed to be caused by vacuum fluctuations, but naive calculations give results in stark disagreement with fact. In the Casimir effect, vacuum fluctuations cause forces in dielectric media, which is very well described by Lifshitz theory. Recently, using the analogy between geometries and media, a cosmological constant of the correct order of magnitude was calculated with Lifshitz theory (Leonhardt 2019 Ann. Phys. (New York) 411, 167973. (doi:10.1016/j.aop.2019.167973)). This paper discusses the empirical evidence and the ideas behind the Lifshitz theory of the cosmological constant without requiring prior knowledge of cosmology and quantum field theory.This article is part of a discussion meeting issue ‘The next generation of analogue gravity experiments’.

  • Integrated Experimental and Theoretical Approach for Efficient Design and Synthesis of Gold-Based Double Halide Perovskites

    Bajorowicz B., Mikolajczyk A., Pinto H. P., Miodyńska M., Lisowski W., Klimczuk T., Kaplan-Ashiri I., Kazes M., Oron D. & Zaleska-Medynska A. (2020) Journal of Physical Chemistry C.
    Applied cutting-edge electronic structure and phonon simulations provide a reliable knowledge about the stability of perovskite structures and their electronic properties, which are crucial for design of effective nanomaterials. Gold is one of the exceptional elements, which can exist both as a monovalent and a trivalent ion in the B site of a double perovskite such as A2BIBIIIX6. However, until now, electronic properties of Cs2AuIAuIIIX6 have not been sufficiently explored and this material was never synthesized using Au1+ and Au3+ precursors in the preparation route. Here, computational simulations combined with an experimental study provide new insight into the properties and synthesis route of Cs2AuIAuIIIX6 (X = Cl, Br, and I) perovskites. First-principles calculations reveal that tetragonal Cs2AuIAuIIIX6 (X = I, Br, Cl) molecules present a band gap of 1.10, 1.15, and 1.40 eV, respectively. Application of novel approaches in the simulations of the VB-XPS for Cs2AuIAuIIICl6 allows replication of the observed spectrum and provides strong evidence of the reliability of the obtained results for the other perovskites Cs2AuIAuIIIX6, X = Br, I. Following theoretical findings, a one-step preparation route of the Cs2AuIAuIIICl6 is developed using a combination of monovalent and trivalent gold precursors at a relatively low temperature. It should be emphasized that this is the first synthesis of this material at low temperatures, allowing for obtaining highly crystalline Cs2Au2Cl6 particles with controlled morphology and without gold impurities. The band gap of synthesized Cs2AuIAuIIICl6 is extended into the NIR spectral range, where most other double perovskites are limited to higher energies, limiting their usage in single junction solar cells or in photocatalysis. The as-synthesized Cs2AuIAuIIICl6 exhibits high efficiency in a photocatalytic toluene degradation reaction under visible light irradiation. The developed approach provides information necessary for structure manipulation at the early stage of its synthesis and offers a new and useful guidance for design of novel improved lead-free inorganic halide perovskite with interesting optical and photocatalytic properties.

  • Temperature Dependence of Excitonic and Biexcitonic Decay Rates in Colloidal Nanoplatelets by Time-Gated Photon Correlation

    Benjamin E., Yallapragada V. J., Amgar D., Yang G., Tenne R. & Oron D. (2020) Journal of Physical Chemistry Letters.
    Excitons in colloidal semiconductor nanoplatelets (NPLs) are weakly confined in the lateral dimensions. This results in significantly smaller Auger rates and, consequently, larger biexciton quantum yields, when compared to spherical quantum dots (QDs). Here we report a study of the temperature dependence of the biexciton Auger rate in individual CdSe/CdS core-shell NPLs, through the measurement of time-gated second-order photon correlations in the photoluminescence. We also utilize this method to directly estimate the single-exciton radiative rate. We find that whereas the radiative lifetime of NPLs increases with temperature, the Auger lifetime is almost temperature-independent. Our findings suggest that Auger recombination in NPLs is qualitatively similar to that of semiconductor quantum wells. Time-gated photon correlation measurements offer the unique ability to study multiphoton emission events, while excluding effects of competing fast processes, and can provide significant insight into the photophysics of a variety of nanocrystal multiphoton emitters.

  • A highly reflective biogenic photonic material from core-shell birefringent nanoparticles

    Palmer B. A., Yallapragada V. J., Schiffmann N., Wormser E. M., Elad N., Aflalo E. D., Sagi A., Weiner S., Addadi L. & Oron D. (2020) Nature Nanotechnology.
    The birefringence of isoxanthopterin crystalline spherulites enhances the reflectivity of a biological photonic crystal.Spectacular natural optical phenomena are produced by highly reflective assemblies of organic crystals. Here we show how the tapetum reflector in a shrimp eye is constructed from arrays of spherical isoxanthopterin nanoparticles and relate the particle properties to their optical function. The nanoparticles are composed of single-crystal isoxanthopterin nanoplates arranged in concentric lamellae around a hollow core. The spherulitic birefringence of the nanoparticles, which originates from the radial alignment of the plates, results in a significant enhancement of the back-scattering. This enables the organism to maximize the reflectivity of the ultrathin tapetum, which functions to increase the eye's sensitivity and preserve visual acuity. The particle size, core/shell ratio and packing are also controlled to optimize the intensity and spectral properties of the tapetum back-scattering. This system offers inspiration for the design of photonic crystals constructed from spherically symmetric birefringent particles for use in ultrathin reflectors and as non-iridescent pigments.

  • Optical quantum memory with optically inaccessible noble-gas spins

    Katz O., Reches E., Shaham R., Gorshkov A. V. & Firstenberg O. (2020) arXiv.
    Optical quantum memories, which store and preserve the quantum state of photons, rely on a coherent mapping of the photonic state onto matter states that are optically accessible. Here we outline a new physical mechanism to map the state of photons onto the long-lived but optically inaccessible collective state of noble-gas spins. The mapping employs the coherent spin-exchange interaction arising from random collisions with alkali vapor. We analyze optimal strategies for high-efficiency storage and retrieval of non-classical light at various parameter regimes. Based on these strategies, we identify feasible experimental conditions for realizing efficient quantum memories with noble-gas spins having hours-long coherence times at room temperature and above

  • Composite-fringe atom interferometry for high dynamic-range sensing

    Avinadav C., Yankelev D., Firstenberg O. & Davidson N. (2020) Physical Review Applied.
    Atom interferometers offer excellent sensitivity to gravitational and inertial signals but have limited dynamic range. We introduce a scheme that improves this trade-off by a factor of 50 using composite fringes, obtained from sets of measurements with slightly varying interrogation times, as in a moire effect. We analyze analytically the performance gain in this approach and the trade-offs it entails between sensitivity, dynamic range, and bandwidth, and we experimentally validate the analysis over a wide range of parameters. Combining composite-fringe measurements with a particle-filter estimation protocol, we demonstrate continuous tracking of a rapidly varying signal over a span 2 orders of magnitude larger than the dynamic range of a traditional atom interferometer.

  • Laser-plasma proton acceleration with a combined gas-foil target

    Levy D., Bernert C., Rehwald M., Andriyash I. A., Assenbaum S., Kluge T., Kroupp E., Obst-Huebl L., Pausch R., Schulze-Makuch A., Zeil K., Schramm U. & Malka V. (2020) New Journal of Physics.
    Laser-plasma proton acceleration was investigated in the target normal sheath acceleration regime with a target composed of a gas layer and a thin foil. The laser's shape, duration, energy and frequency are modified as it propagates in the gas, altering the laser-solid interaction leading to proton acceleration. The modified properties of the laser were assessed by both numerical simulations and by measurements. The 3D particle-in-cell simulations have shown that a nearly seven-fold increase in peak intensity at the foil plane is possible. In the experiment, maximum proton energies showed high dependence on the energy transmission of the laser through the gas and a lesser dependence on the size and shape of the pulse. At high gas densities, where high intensity was expected, laser energy depletion and pulse distortion suppressed proton energies. At low densities, with the laser focused far behind the foil, self-focusing was observed and the gas showed a positive effect on proton energies. The promising results of this first exploration motivate further study of the target.

  • Observation of Spin-Spin Fermion-Mediated Interactions between Ultracold Bosons

    Edri H., Raz B., Matzliah N., Davidson N. & Ozeri R. (2020) Physical Review Letters.
    Interactions in an ultracold boson-fermion mixture are often manifested by elastic collisions. In a mixture of a condensed Bose gas (BEC) and spin polarized degenerate Fermi gas (DFG), fermions can mediate spin-spin interactions between bosons, leading to an effective long-range magnetic interaction analogous to Ruderman-Kittcl-Kasuya-Yosida [Phys. Rev. 96, 99 (1954); Prog. Theor. Phys. 16, 45 (1956); Phys. Rev. 106, 893 (1957)] interaction in solids. We used Ramsey spectroscopy of the hyperfine clock transition in a Rb-87 BEC to measure the interaction mediated by a K-40 DFG. By controlling the boson density we isolated the effect of mediated interactions from mean-field frequency shifts due to direct collision with fermions. We measured an increase of boson spin-spin interaction by a factor of eta = 1.45 +/- 0.05(stat) +/- 0.13(syst) in the presence of the DFG, providing clear evidence of spin-spin fennion mediated interaction. Decoherence in our system was dominated by inhomogeneous boson density shift, which increased significantly in the presence of the DFG, again indicating mediated interactions. We also measured a frequency shift due to boson-fermion interactions in accordance with a scattering length difference of a(bf2) - a(bf1) = -5.36 +/- 0.44(stat) +/- 1.43(syst)a(0) between the clock-transition states, a first measurement beyond the low-energy elastic approximation [R. Cote, & A. Dalgarno, H. Wang, and W. C. Stwalley, Phys. Rev. A 57, R4118 (1998); A. Dalgarno and M. Rudge, Proc. R. Soc. A 286, 519 (1965)] in this mixture. This interaction can be tuned with a future use of a boson-fermion Feshbach resonance. Fermion-mediated interactions can potentially give rise to interesting new magnetic phases and extend the Bose-Hubbard model when the atoms are placed in an optical lattice.

  • Laser plasma accelerators

    Tajima T. & Malka J. (2020) Plasma Physics and Controlled Fusion.
    An ultrafast intense laser pulse drives coherent wakefields of relativistic amplitude with a high phase velocity robustly supported by the plasma. The structures of wakes and sheaths in plasma are contrasted. While the large amplitude of wakefields involves collective resonant oscillations of the eigenmode of the entire population of plasma electrons, the wake phase velocity ~c and ultrafast nature of the laser pulse introduce the wake stability and rigidity. When the phase velocity decreases, wakefields turn into sheaths, which are more suitable for ion acceleration. This short review reports on 4 decades of discoveries on laser plasma accelerators.

  • Quantum metasurfaces with atom arrays

    Bekenstein R., Pikovski I., Pichler H., Shahmoon E., Yelin S. F. & Lukin M. D. (2020) Nature Physics.
    Metasurfaces mould the flow of classical light waves by engineering subwavelength patterns from dielectric or metallic thin films. We introduce and analyse a method in which quantum operator-valued reflectivity can be used to control both the spatiotemporal and quantum properties of transmitted and reflected light. Such quantum metasurfaces are realized by entangling the macroscopic response of atomically thin atom arrays to light. We show that such a system allows for parallel quantum operations between atoms and photons as well as for the generation of highly entangled photonic states such as photonic Greenberger–Horne–Zeilinger and three-dimensional cluster states suitable for quantum information processing. We analyse the influence of imperfections as well as specific implementations based on atom arrays excited into Rydberg states.

  • COXINEL transport of laser plasma accelerated electrons

    Espinos D. O., Ghaith A., Loulergue A., Andre T., Kitegi C., Sebdaoui M., Marteau F., Blache F., Valleau M., Labat M., Lestrade A., Roussel E., Thaury C., Corde S., Lambert G., Kononenko O., Goddet J., Tafzi A., Andriyash I., Malka V. & Couprie M. (2020) Plasma Physics and Controlled Fusion.
    Laser plasma acceleration (LPA) enables the generation of an up to several GeV electron beam with a short bunch length and high peak current within a centimeter scale. In view of undulator type light source applications, electron beam manipulation has to be applied. We report here on detailed electron beam transport for an LPA electron beam on the COXINEL test line, that consists of strong permanent quadrupoles to handle the electron beam divergence, a magnetic chicane to reduce the energy spread and a second set of quadrupoles for adjusting the focusing inside the undulator. After describing the measured LPA characteristics, we show that we can properly transport the electron beam along the line, thanks to several screens. We also illustrate the influence of the chromatic effects induced by the electron beam energy spread, both experimentally and numerically. We then study the sensitivity of the transport to the electron beam pointing and skewed quadrupolar components.

  • Direct observation of ultracold atom-ion excitation exchange

    Ben-Shlomi R., Vexiau R., Meir Z., Sikorsky T., Akerman N., Pinkas M., Dulieu O. & Ozeri R. (2020) Physical Review A.
    Ultracold atom-ion collisions are an emerging field of research that can ultimately lead to their precise quantum control. In collisions in which the ion is prepared in an excited state, previous studies showed that the dominant reaction pathway was charge exchange. Here, we explored the outcome products and the energy released from a single ultracold collision between a single Sr+88 ion and a single Rb87 atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived D5/2 and D3/2 states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.

  • Quantum-nondemolition state detection and spectroscopy of single trapped molecules

    Sinhal M., Meir Z., Najafian K., Hegi G. & Willitsch S. (2020) Science (American Association for the Advancement of Science).
    Trapped atoms and ions, which are among the best-controlled quantum systems, find widespread applications in quantum science. For molecules, a similar degree of control is currently lacking owing to their complex energy-level structure. Quantum-logic protocols in which atomic ions serve as probes for molecular ions are a promising route for achieving this level of control, especially for homonuclear species that decouple from blackbody radiation. Here, a quantum-nondemolition protocol on single trapped N+2 molecules is demonstrated. The spin-rovibronic state of the molecule is detected with >99% fidelity, and a spectroscopic transition is measured without destroying the quantum state. This method lays the foundations for new approaches to molecular spectroscopy, state-to-state chemistry, and the implementation of molecular qubits.

  • Structured beams invariant to coherent diffusion

    Smartsev S., Chriki R., Eger D., Firstenberg O. & Davidson N. (2020) Optics Express.
    Bessel beams are renowned members of a wide family of non-diffracting (propagationinvariant) fields. We report on experiments showing that non-diffracting fields are also immune to diffusion. We map the phase and magnitude of structured laser fields onto the spatial coherence between two internal states of warm atoms undergoing diffusion. We measure the field after a controllable, effective, diffusion time by continuously generating light from the spatial coherence. The coherent diffusion of Bessel-Gaussian fields and more intricate, non-diffracting fields is quantitatively analyzed and directly compared to that of diffracting fields. To elucidate the origin of diffusion invariance, we show results for non-diffracting fields whose phase pattern we flatten.

  • SOFISM: Super-resolution optical fluctuation image scanning microscopy

    Sroda A., Makowski A., Tenne R., Rossman U., Lubin G., Oron D. & Lapkiewicz R. (2020) Optica.
    Super-resolution optical microscopy is a rapidly evolving scientific field dedicated to imaging sub-wavelength-sized objects, leaving its mark in multiple branches of biology and technology. While several super-resolution optical microscopy methods have become a common tool in life science imaging, new methods, supported by cutting-edge technology, continue to emerge. One rather recent addition to the super-resolution toolbox, image scanning microscopy (ISM), achieves up to twofold lateral resolution enhancement in a robust and straightforward manner. To further enhance ISM's resolution in all three dimensions, we present and experimentally demonstrate here super-resolution optical fluctuation ISM (SOFISM). Measuring the fluorescence fluctuation contrast in an ISM architecture, we obtain images with a ×2.5 lateral resolution beyond the diffraction limit along with an enhanced axial resolution for a fixed cell sample labeled with commercially available quantum dots. The inherent temporal averaging of the ISM technique enables image acquisition of the fluctuation correlation contrast within millisecond-scale pixel dwell times. SOFISM can therefore offer a robust path to achieve high-resolution images within a slightly modified confocal microscope, using standard fluorescent labels and reasonable acquisition times.

  • Cavity quantum optomechanics with an atom-array membrane

    Shahmoon E., Wild D. S., Lukin M. D. & Yelin S. F. (2020) arXiv.
    We consider a quantum optomechanical scheme wherein an ordered two-dimensional array of laser-trapped atoms is used as a movable membrane. The extremely light mass of the atoms yields very strong optomechanical coupling, while their spatial order largely eliminates scattering losses. We show that this combination opens the way for quantum optomechanical nonlinearities, well within the ultimate single-photon strong-coupling regime. As an example, we analyze the possibility to observe optomechanically induced quantum effects such as photon blockade and time-delayed non-classical correlations. We discuss novel opportunities opened by the optomechanical backaction on the internal states of the array atoms.

  • Fluorescence and Optical Activity of Chiral CdTe Quantum Dots in Their Interaction with Amino Acids

    Li G., Fei X., Liu H., Gao J., Nie J., Wang Y., Tian Z., He C., Wang J., Ji C., Oron D. & Yang G. (2020) ACS Nano.
    Ligand-induced chirality in semiconducting nanocrystals has been the subject of extensive study in the past few years and shows potential applications in optics and biology. Yet, the origin of the chiroptical effect in semiconductor nanoparticles is still not fully understood. Here, we examine the effect of the interaction with amino acids on both the fluorescence and the optical activity of chiral semiconductor quantum dots (QDs). A significant fluorescence enhancement is observed for L/D-Cys-CdTe QDs upon interaction with all the tested amino acids, indicating suppression of non-radiative pathways as well as the passivation of surface trap sites brought via the interaction of the amino group with the CdTe QDs' surface. Hetero-chiral amino acids are shown to weaken the Circular Dichroism (CD) signal, which may be attributed to a different binding configuration of cysteine molecules on the QDs surface. Furthermore, a red shift of both CD and fluorescence signals in L/D-Cys-CdTe QDs is only observed upon adding cysteine, while other tested amino acids do not exhibit such an effect. We speculate that the thiol group induces orbital hybridization of the highest occupied molecular orbital (HOMOs) of cysteine and the valance band of CdTe QDs, leading to the decrease of the energy band-gap and a concomitant red shift of CD and fluorescence spectra. This is further verified by density functional theory (DFT) calculations. Both the experimental and theoretical findings indicate that the addition of ligands which do not "directly" interact with the VB of the QD (non-cysteine moieties) changes the QD photophysical properties as it probably modifies the way cysteine is bound to the surface. Hence, we conclude that it is not only the chemistry of the amino acid ligand which affects both CD and PL, rather, it is also the exact geometry of binding which modifies these properties. Understanding the relationship between QD's surface and chiral amino acid thus provides an additional perspective on the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, potentially enabling us to optimize the design of chiral semiconductor QDs for chiroptic applications.

  • Low Frequency Collinear Pre-Resonant Impulsive Stimulated Raman Microspectroscopy

    Soffer Y., Raanan D. & Oron D. (2020) ACS Photonics.
    In this work, we extend low frequency impulsive stimulated Raman microspectroscopy to the pre-electronic resonance regime, using a broadband two-color collinear pump probe scheme which can be readily extended to imaging. We discuss the difficulties unique to this type of measurements in the form of competing resonant two-photon absorption processes and the means to overcome them, and successfully reduce the noise which arises due to those competing processes by eliminating the detected spectral components which do not contribute to the vibrational signature of the sample yet introduce most of the noise. Finally, we demonstrate low frequency spectroscopy of crystalline samples under near-resonant pumping showing both enhancement and spectral modification due to coupling with the electronic degree of freedom.

  • Quantum dynamics of collective spin states in a thermal gas

    Shaham R., Katz O. & Firstenberg O. (2020) Physical Review A.
    Ensembles of alkali-metal or noble-gas atoms at room temperature and above are widely applied in quantum optics and metrology owing to their long-lived spins. Their collective spin states maintain nonclassical nonlocal correlations, despite the atomic thermal motion in the bulk and at the boundaries. Here we present a stochastic, fully quantum description of the effect of atomic diffusion in these systems. We employ the Bloch-Heisenberg-Langevin formalism to account for the quantum noise originating from diffusion and from various boundary conditions corresponding to typical wall coatings, thus modeling the dynamics of nonclassical spin states with spatial interatomic correlations. As examples, we apply the model to calculate spin noise spectroscopy, temporal relaxation of squeezed spin states, and the coherent coupling between two spin species in a hybrid system.

  • Effect of ion-trap parameters on energy distributions of ultra-cold atom-ion mixtures

    Pinkas M., Meir Z., Sikorsky T., Ben-Shlomi R., Akerman N. & Ozeri R. (2020) New Journal of Physics.
    Experiments in which ultra-cold neutral atoms and charged ions are overlapped, constitute a new field in atomic and molecular physics, with applications ranging from studying out-of-equilibrium dynamics to simulating quantum many-body systems. The holy grail of ion-neutral systems is reaching the quantum low-energy scattering regime, known as the s-wave scattering. However, in most atom-ion systems, there is a fundamental limit that prohibits reaching this regime. This limit arises from the time-dependent trapping potential of the ion, the Paul trap, which sets a lower collision energy limit which is higher than the s-wave energy. In this work, we studied both theoretically and experimentally, the way the Paul trap parameters affect the energy distribution of an ion that is immersed in a bath of ultra-cold atoms. Heating rates and energy distributions of the ion are calculated for various trap parameters by a molecular dynamics (MD) simulation that takes into account the attractive atom-ion potential. The deviation of the energy distribution from a thermal one is discussed. Using the MD simulation, the heating dynamics for different atom-ion combinations is also investigated. In addition, we performed measurements of the heating rates of a ground-state cooled Sr-88(+) ion that is immersed in an ultra-cold cloud of Rb-87 atoms, over a wide range of trap parameters, and compare our results to the MD simulation. Both the simulation and the experiment reveal no significant change in the heating for different parameters of the trap. However, in the experiment a slightly higher global heating is observed, relative to the simulation.

  • High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits

    Elder S. S., Wang C. S., Reinhold P., Hann C. T., Chou K. S., Lester B. J., Rosenblum S., Frunzio L., Jiang L. & Schoelkopf R. J. (2020) Physical Review X.
    Qubit measurements are central to quantum information processing. In the field of superconducting qubits, standard readout techniques are limited not only by the signal-to-noise ratio, but also by state relaxation during the measurement. In this work, we demonstrate that the limitation due to relaxation can be suppressed by using the many-level Hilbert space of superconducting circuits: In a multilevel encoding, the measurement is corrupted only when multiple errors occur. Employing this technique, we show that we can directly resolve transmon gate errors at the level of one part in 10(3). Extending this idea, we apply the same principles to the measurement of a logical qubit encoded in a bosonic mode and detected with a transmon ancilla, implementing a proposal by Hann et al. [Phys. Rev. A 98, 022305 (2018)]. Qubit state assignments are made based on a sequence of repeated readouts, further reducing the overall infidelity. This approach is quite general, and several encodings are studied; the codewords are more distinguishable when the distance between them is increased with respect to photon loss. The trade-off between multiple readouts and state relaxation is explored and shown to be consistent with the photon-loss model. We report a logical assignment infidelity of 5.8 x 10(-5) for a Fock-based encoding and 4.2 x 10 (-3) for a quantum error correction code (the S = 2, N = 1 binomial code). Our results not only improve the fidelity of quantum information applications, but also enable more precise characterization of process or gate errors.

  • Recovering the Homogeneous Absorption of Inhomogeneous Media

    Lahad O., Finkelstein R., Davidson O., Michel O., Poem E. & Firstenberg O. (2019) Physical Review Letters.
    The resonant absorption of light by an ensemble of absorbers decreases when the resonance is in homogeneously broadened. Recovering the lost absorption cross section is of great importance for various applications of light-matter interactions, particularly in quantum optics, but no recovery mechanism has yet been identified and successfully demonstrated. Here, we formulate the limit set by the inhomogeneity on the absorption, and present a mechanism able to circumvent this limit and fully recover the homogeneous absorption of the ensemble. We experimentally study this mechanism using two different level schemes in atomic vapors and demonstrate up to fivefold enhancement of the absorption above the inhomogeneous limit. Our scheme relies on light shifts induced by auxiliary fields and is thus applicable to various physical systems and inhomogeneity mechanisms.

  • Cherenkov radiation of light bullets

    Leonhardt U. & Rosenberg Y. (2019) Physical Review A.
    Electrically charged particles, moving faster than the speed of light in a medium, emit Cherenkov radiation. Theory predicts electric and magnetic dipoles to radiate as well, with a puzzling behavior for magnetic dipoles pointing in transversal direction [I. M. Frank, Izv. Akad. Nauk SSSR, Ser. Fiz. 6, 3 (1942)]. A discontinuous Cherenkov spectrum should appear at threshold, where the particle velocity matches the phase velocity of light. Here we deduce theoretically that light bullets [Y. Silberberg, Opt. Lett. 15, 1282 (1990)OPLEDP0146-959210.1364/OL.15.001282] emit an analogous radiation with exactly the same spectral discontinuity for point-like sources. For extended sources the discontinuity turns into a spectral peak at threshold. We argue that this Cherenkov radiation has been experimentally observed in the first attempt to measure Hawking radiation in optics [F. Belgiorno, Phys. Rev. Lett. 105, 203901 (2010)PRLTAO0031-900710.1103/PhysRevLett.105.203901] thus giving experimental evidence for a puzzle in Cherenkov radiation instead.

  • Skew Quadrupole Effect of Laser Plasma Electron Beam Transport

    Espinos D. O., Ghaith A., Andre T., Kitegi C., Sebdaoui M., Loulergue A., Marteau F., Blache F., Valleau M., Labat M., Lestrade A., Roussel E., Thaury C., Corde S., Lambert G., Kononenko O., Goddet J., Tafzi A., Malka V. & Couprie M. (2019) Applied sciences-Basel.
    Laser plasma acceleration (LPA) capable of providing femtosecond and GeV electron beams in cm scale distances brings a high interest for different applications, such as free electron laser and future colliders. Nevertheless, LPA high divergence and energy spread require an initial strong focus to mitigate the chromatic effects. The reliability, in particular with the pointing fluctuations, sets a real challenge for the control of the dispersion along the electron beam transport. We examine here how the magnetic defects of the first strong quadrupoles, in particular, the skew terms, can affect the brightness of the transported electron beam, in the case of the COXINEL transport line, designed for manipulating the electron beam properties for a free electron laser application. We also show that the higher the initial beam divergence, the larger the degradation. Experimentally, after having implemented a beam pointing alignment compensation method enabling us to adjust the position and dispersion independently, we demonstrate that the presence of non-negligible skew quadrupolar components induces a transversal spread and tilt of the beam, leading to an emittance growth and brightness reduction. We are able to reproduce the measurements with beam transport simulations using the measured electron beam parameters.

  • Generation of optical Fock and W states with single-atom-based bright quantum scissors

    Aqua Z., Kim M. & Dayan B. (2019) Photonics Research.
    We introduce a multi-step protocol for optical quantum state engineering that performs as “bright quantum scissors,” namely truncating an arbitrary input quantum state to have at least a certain number of photons. The protocol exploits single-photon pulses and is based on the effect of single-photon Raman interaction, which is implemented with a single three-level Λ system (e.g., a single atom) Purcell-enhanced by a single-sided cavity. A single step of the protocol realizes the inverse of the bosonic annihilation operator. Multiple iterations of the protocol can be used to deterministically generate a chain of single photons in a W state. Alternatively, upon appropriate heralding, the protocol can be used to generate Fock-state optical pulses. This protocol could serve as a useful and versatile building block for the generation of advanced optical quantum states that are vital for quantum communication, distributed quantum information processing, and all-optical quantum computing.

  • Rapid quantum image scanning microscopy by joint sparse reconstruction

    Rossman U., Tenne R., Solomon O., Kaplan-Ashiri I., Dadosh T., Eldar Y. C. & Oron D. (2019) Optica.
    The evolution of experimental superresolution microscopy has been accompanied by the development of advanced computational imaging capabilities. Recently introduced, quantum image scanning microscopy (Q-ISM) has successfully harnessed quantum correlations of light to establish an improved viable imaging modality that builds upon the preceding image scanning microscopy (ISM) superresolution method. While offering improved resolution, at present the inherently weak signal demands exhaustively long acquisition periods. Here we exploit the fact that the correlation measurement in Q-ISM is complementary to the standard ISM data, acquired simultaneously, and demonstrate joint sparse recovery from Q-ISM and ISM images. Reconstructions from images of fluorescent quantum dots are validated through correlative electron microscope measurements, and exhibit superior resolution enhancement as compared to Q-ISM images. In addition, the algorithmic fusion facilitates a drastic reduction in the requisite measurement duration, since low signal-to-noise-ratio Q-ISM measurements suffice for augmenting ISM images. Finally, we obtain enhanced superresolved reconstructions from short scans of a biological sample labeled with quantum dots, demonstrating the potential of our method for quantum imaging in life science microscopy.

  • PbS quantum dots as additives in methylammonium halide perovskite solar cells: the effect of quantum dot capping

    Thi Tuyen Ngo, Masi S., Mendez P. F., Kazes M., Oron D. & Mora Sero I. (2019) Nanoscale Advances.
    Colloidal PbS quantum dots (QDs) have been successfully employed as additives in halide perovskite solar cells (PSCs) acting as nucleation centers in the perovskite crystallization process. For this strategy, the surface functionalization of the QDs, controlled via the use of different capping ligands, is likely of key importance. In this work, we examine the influence of the PbS QD capping on the photovoltaic performance of methylammonium lead iodide PSCs. We test PSCs fabricated with PbS QD additives with different capping ligands including methylammonium lead iodide (MAPI), cesium lead iodide (CsPI) and 4-aminobenzoic acid (ABA). Both the presence of PbS QDs and the specific capping used have a significant effect on the properties of the deposited perovskite layer, which affects, in turn, the photovoltaic performance. For all capping ligands used, the inclusion of PbS QDs leads to the formation of perovskite films with larger grain size, improving, in addition, the crystalline preferential orientation and the crystallinity. Yet, differences between the capping agents were observed. The use of QDs with ABA capping had a higher impact on the morphological properties while the employment of the CsPI ligand was more effective in improving the optical properties of the perovskite films. Taking advantage of the improved properties, PSCs based on the perovskite films with embedded PbS QDs exhibit an enhanced photovoltaic performance, showing the highest increase with ABA capping. Moreover, bulk recombination via trap states is reduced when the ABA ligand is used for capping of the PbS QD additives in the perovskite film. We demonstrate how surface chemistry engineering of PbS QD additives in solution-processed perovskite films opens a new approach towards the design of high quality materials, paving the way to improved optoelectronic properties and more efficient photovoltaic devices.

  • Controlling Subcycle Optical Chirality in the Photoionization of Chiral Molecules

    Rozen S., Comby A., Bloch E., Beauvarlet S., Descamps D., Fabre B., Petit S., Blanchet V., Pons B., Dudovich N. & Mairesse Y. (2019) Physical Review X.
    Controlling the polarization state of electromagnetic radiation enables the investigation of fundamental symmetry properties of matter through chiroptical processes. Over the past decades, many strategies have been developed to reveal structural or dynamical information about chiral molecules with high sensitivity, from the microwave to the extreme ultraviolet range. Most schemes employ circularly or elliptically polarized radiation, and more sophisticated configurations involve, for instance, light pulses with time-varying polarization states. All these schemes share a common property-the polarization state of light is always considered as constant over one optical cycle. In this study, we focus on the optical cycle in order to resolve and control a subcyle chiroptical process. We engineer an electric field whose instantaneous chirality can be controlled within the optical cycle, by combining two phase-locked orthogonally polarized fundamental and second harmonic fields. While the composite field has zero net ellipticity, it shows an instantaneous optical chirality which can be controlled via the two-color delay. We theoretically and experimentally investigate the photoionization of chiral molecules with this controlled chiral field. We find that electrons are preferentially ejected forward or backward relative to the laser propagation direction depending on the molecular handedness, similarly to the well-established photoelectron circular dichroism process. However, since the instantaneous chirality switches sign from one half-cycle to the next, electrons ionized from two consecutive half-cycles of the laser show opposite forward-backward asymmetries. This chiral signal, the enantiosensitive subcycle antisymmetric response gated by electric-field rotation, provides a unique insight into the influence of instantaneous chirality in the dynamical photoionization process. More generally, our results demonstrate the important role of subcycle polarization shaping of electric fields as a new route to study and manipulate chiroptical processes.

  • Coupling of laser arrays with intracavity elements in the far-field

    Mahler S., Tradonsky C., Chriki R., Friesem A. A. & Davidson N. (2019) OSA Continuum.
    A relatively simple technique for coupling lasers in an array is presented. It is based on the insertion of an intracavity optical element in the far-field plane of a degenerate cavity laser that is used to form an array of lasers. We show that it is possible to control the selection of the lasers to couple regardless of the array geometry. An intracavity spherical lens in the far-field plane is numerically and experimentally investigated and the results compared with those from the more complicated Talbot diffraction for coupling lasers. With an intracavity cylindrical lens in a two dimensional square array geometry, it is possible to obtain controlled one-dimensional coupling, and with an intracavity binary phase element it is possible to obtain versatile couplings.

  • Compact reflective system for ideal imaging concentration

    Bokor N., Jahn K. & Davidson N. (2019) Applied Optics.
    We propose a new design principle for optimal concentration of light with small diffusivity based on the conservation of local brightness in passive optical transformations. A coordinate transformation is applied on the incoming rays to compensate for the variations in local brightness by the focusing stage. We apply this analytic design for a compact reflective configuration for ideal imaging concentration of diffuse light such as sunlight in one dimension on an elongated target with arbitrary cross-sectional shape at the thermodynamic limit. As illustrations, we present the design for two different target geometries and verify its validity using numerical ray-tracing simulations. The same configuration can be used in reverse as an ideal collimator of a finite diffuse source. (C) 2019 Optical Society of America

  • Status of the Horizon 2020 EuPRAXIA conceptual design study

    Weikum M. K., Akhter T., Alesini D., Andriyash I. A. & Malka V. (2019) Journal of Physics Conference Series.
    The Horizon 2020 project EuPRAXIA (European Plasma Research Accelerator with eXcellence In Applications) is producing a conceptual design report for a highly compact and cost-effective European facility with multi-GeV electron beams accelerated using plasmas. EuPRAXIA will be set up as a distributed Open Innovation platform with two construction sites, one with a focus on beam-driven plasma acceleration (PWFA) and another site with a focus on laser-driven plasma acceleration (LWFA). User areas at both sites will provide access to free-electron laser pilot experiments, positron generation and acceleration, compact radiation sources, and test beams for high-energy physics detector development. Support centres in four different countries will complement the pan-European implementation of this infrastructure.

  • Comment on Self-Stress on a Dielectric Ball and Casimir-Polder Forces

    Leonhardt U. (2019) arxiv.org.
    In our paper [Ann. Phys. (NY) 395, 326 (2018)] we calculate the Casimir stress on a sphere immersed in a homogeneous background, assuming dispersionless dielectrics. Our results appear to challenge the conventional picture of Casimir forces. The paper [arXiv:1909.05721] criticises our approach without offering an alternative. In particular, the paper [arXiv:1909.05721] claims that we have made an unjustified mathematical step. This brief comment clarifies the matter.

  • Double-blind holography of attosecond pulses

    Pedatzur O., Trabattoni A., Leshem B., Shalmoni H., Castrovilli M. C., Galli M., Lucchini M., Mansson E., Frassetto F., Poletto L., Nadler B., Raz O., Nisoli M., Calegari F., Oron D. & Dudovich N. (2019) Nature Photonics.
    A key challenge in attosecond science is the temporal characterization of attosecond pulses that are essential for understanding the evolution of electronic wavefunctions in atoms, molecules and solids(1-7). Current characterization methods, based on nonlinear light-matter interactions, are limited in terms of stability and waveform complexity. Here, we experimentally demonstrate a conceptually new linear and all-optical pulse characterization method, inspired by double-blind holography. Holography is realized by measuring the extreme ultraviolet (XUV) spectra of two unknown attosecond signals and their interference. Assuming a finite pulse duration constraint, we reconstruct the missing spectral phases and characterize the unknown signals in both isolated pulse and double pulse scenarios. This method can be implemented in a wide range of experimental realizations, enabling the study of complex electron dynamics via a single-shot and linear measurement.

  • In situ growth of alpha-CsPbI3 perovskite nanocrystals on the surface of reduced graphene oxide with enhanced stability and carrier transport quality

    Zhang Q., Nan H., Zhou Y., Gu Y., Tai M., Wei Y., Hao F., Li J., Oron D. & Lin H. (2019) Journal of Materials Chemistry C.
    Herein, an in situ solution growth method to prepare preferentially assembled and well-distributed alpha-CsPbI3 nanocrystals (NCs)/reduced graphene oxide (rGO) heterostructures is presented. Owing to its excellent thermal conductivity, carrier mobility, hydrophobic nature and passivation effect, rGO could reduce the number of ligands on the surface of alpha-CsPbI3 NCs, provide protection against air and moisture, and enhance the carrier separation and carrier transport properties of nanocrystals. The homogeneous growth of nanocrystals and their distribution along the surface of rGO also improved the stability and carrier transport quality compared to that of alpha-CsPbI3 NCs. Particularly, alpha-CsPbI3 NCs/rGO heterostructures show a suitable band gap of B1.74 eV, an acceptable photoluminescence (PL) intensity and a PL quantum yield (PLQY) of similar to 10.7%. The decay lifetime of these heterostructures was maintained at similar to 43.5 ns and PLQY was maintained at similar to 68% of the initial value when stored in ambient conditions for similar to 4 weeks. Finally, we demonstrate the inkjet printing of these heterostructures, manifesting their favorable dispersibility in organic solvents, and showing their utility as optically active materials for applications in optoelectronic devices.

  • Excitation and Emission Transition Dipoles of Type-II Semiconductor Nanorods

    Ghosh S., Chizhik A. M., Yang G., Karedla N., Gregor I., Oron D., Weiss S., Enderlein J. & Chizhik A. (2019) Nano Letters.
    The mechanisms of exciton generation and recombination in semiconductor nanocrystals are crucial to the understanding of their photophysics and for their application in nearly all fields. While many studies have been focused on type-I heterojunction nanocrystals, the photophysics of type-II nanorods, where the hole is located in the core and the electron is located in the shell of the nanorod, remain largely unexplored. In this work, by scanning single nanorods through the focal spot of radially and azimuthally polarized laser beams and by comparing the measured excitation patterns with a theoretical model, we determine the dimensionality of the excitation transition dipole of single type-II nanorods. Additionally, by recording defocused patterns of the emission of the same particles, we measure their emission transition dipoles. The combination of these techniques allows us to unambiguously deduce the dimensionality and orientation of both excitation and emission transition dipoles of single type-II semiconductor nanorods. The results show that in contrast to previously studied quantum emitters, the particles possess a 3D degenerate excitation and a fixed linear emission transition dipole.

  • Sub-second hyper-spectral low-frequency vibrational imaging via impulsive Raman excitation

    Raanan D., Audier X., Shivkumar S., Asher M., Menahem M., Yaffe O., Forget N., Rigneault H. & Oron D. (2019) Optics Letters.
    Real-time vibrational microscopy has been recently demonstrated by various techniques, most of them utilizing the well-known schemes of coherent anti-stokes Raman scattering and stimulated Raman scattering. These techniques readily provide valuable chemical information mostly in the higher vibrational frequency regime (>400 cm(-1)). Addressing the low vibrational frequency regime (

  • Interferometric Attosecond Lock-in Measurement of Extreme Ultraviolet Circular Diehroism

    Kneller O., Azoury D., Kruger M., Bruner B. D., Cohen O., Mairesse Y. & Dudovich N. (2019) .
    Probing vectorial properties of light-matter interactions requires control over the polarization state of light. The generation of extreme-ultraviolet (XUV) attosecond pulses opened new perspectives in measurements of chiral phenomena. Recently, new methods for polarization control in the XUV range, which are based on manipulation of the high harmonic generation (HHG) process were demonstrated [1-4]. However, the limited polarization control in this regime prevents the development of advanced measurement schemes for weak vectorial signals, which require polarization modulation.

  • Quantum correlation measurement with single photon avalanche diode arrays

    Lubin G., Tenne R., Antolovic I. M., Charbon E., Bruschini C. & Oron D. (2019) Optics Express.
    Temporal photon correlation measurement, instrumental to probing the quantum properties of light, typically requires multiple single photon detectors. Progress in single photon avalanche diode (SPAD) array technology highlights their potential as high-performance detector arrays for quantum imaging and photon number-resolving (PNR) experiments. Here, we demonstrate this potential by incorporating a novel on-chip SPAD array with 42% peak photon detection efficiency, low dark count rate and crosstalk probability of 0.14% per detection in a contbcal microscope. This enables reliable measurements of second and third order photon correlations from a single quantum dot emitter. Our analysis overcomes the inter-detector optical crosstalk background even though it is over an order of magnitude larger than our faint signal. To showcase the vast application space of such an approach, we implement a recently introduced super-resolution imaging method, quantum image scanning microscopy (Q-ISM). (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

  • Scalar Dark Matter in the Radio-Frequency Band: Atomic-Spectroscopy Search Results

    Antypas D., Tretiak O., Garcon A., Ozeri R., Perez G. & Budker D. (2019) Physical Review Letters.
    Among the prominent candidates for dark matter are bosonic fields with small scalar couplings to the standard-model particles. Several techniques are employed to search for such couplings, and the current best constraints are derived from tests of gravity or atomic probes. In experiments employing atoms, observables would arise from expected dark-matter-induced oscillations in the fundamental constants of nature. These studies are primarily sensitive to underlying particle masses below 10(-14) eV. We present a method to search for fast oscillations of fundamental constants using atomic spectroscopy in cesium vapor. We demonstrate sensitivity to scalar interactions of dark matter associated with a particle mass in the range 8 x 10(-11) to 4 x 10(-7) eV. In this range our experiment yields constraints on such interactions, which within the framework of an astronomical-size dark matter structure are comparable with, or better than, those provided by experiments probing deviations from the law of gravity.

  • Dynamics of dissipative topological defects in coupled phase oscillators

    Mahler S., Pal V., Tradonsky C., Chriki R., Friesem A. A. & Davidson N. (2019) Journal of Physics B: Atomic, Molecular and Optical Physics.
    The dynamics of topological defects in a system of coupled phase oscillators, arranged in one and two-dimensional arrays, was numerically investigated using the Kuramoto model. After a rapid decay of the number of topological defects, a long-time quasi steady state with few topological defects was detected. Two competing time scales governed the dynamics corresponding to the dissipation rate and the coupling quench rate. The density of topological defects scales as a power law function of the coupling quench rate rho similar to C-nu with nu = 0.25. Reducing the number of topological defects improves the long time coherence and order parameter of the system, enhancing the probability to reach a global minimal loss state that can be mapped to the ground state of a classical XY spin Hamiltonian.

  • Transverse optical pumping of spin states

    Katz O. & Firstenberg O. (2019) Communications Physics.
    Optical pumping is an efficient method for initializing and maintaining atomic spin ensembles in a well-defined quantum spin state. Standard optical pumping methods orient the spins by transferring photonic angular momentum to spin polarization. Generally the spins are oriented along the propagation direction of the light due to selection rules of the dipole interaction. Here we present and experimentally demonstrate that by modulating the light polarization, angular momentum perpendicular to the optical axis can be transferred efficiently to cesium vapor. The transverse pumping scheme employs transversely oriented dark states, allowing for control of the trajectory of the spins on the Bloch sphere. This new mechanism is suitable and potentially beneficial for diverse applications, particularly in quantum metrology.

  • Mathematics of vectorial Gaussian beams

    Levy U., Silberberg Y. & Davidson N. (2019) Adv. Opt. Photon..
    Since the development of laser light sources in the early 1960s, laser beams are everywhere. Laser beams are central in many industrial applications and are essential in ample scientific research fields. Prime scientific examples are optical trapping of ultracold atoms, optical levitation of particles, and laser-based detection of gravitational waves. Mathematically, laser beams are well described by Gaussian beam expressions. Rather well covered in the literature to date are basic expressions for scalar Gaussian beams. In the past, however, higher accuracy mathematics of scalar Gaussian beams and certainly high-accuracy mathematics of vectorial Gaussian beams were far less studied. The objective of the present review then is to summarize and advance the mathematics of vectorial Gaussian beams. When a weakly diverging Gaussian beam, approximated as a linearly polarized two-component plane wave, say (Ex,By), is tightly focused by a high-numerical-aperture lens, the wave is x201C;depolarized.x201D; Namely, the prelens (practically) missing electric field Ey,Ez components suddenly appear. This is similar for the prelens missing Bx,Bz components. In fact, for any divergence angle (x03B8;dlt;1), the ratio of maximum electric field amplitudes of a Gaussian beam Ex:Ez:Ey is roughly 1:x03B8;d2:x03B8;d4. It follows that if a research case involves a tightly focused laser beam, then the case analysis calls for the mathematics of vectorial Gaussian beams. Gaussian-beam-like distributions of the six electricx2013;magnetic vector field components that nearly exactly satisfy Maxwellx2019;s equations are presented. We show that the near-field distributions with and without evanescent waves are markedly different from each other. The here-presented nearly exact six electricx2013;magnetic Gaussian-beam-like field components are symmetric, meaning that the cross-sectional amplitude distribution of Ex(x,y) at any distance (z) is similar to the By(x,y) distribution, Ey(x,y) is similar to Bx(x,y), and a 90x00B0; rotated Ez(x,y) is similar to Bz(x,y). Componentsx2019; symmetry was achieved by executing the steps of an outlined symmetrization procedure. Regardless of how tightly a Gaussian beam is focused, its divergence angle is limited. We show that the full-cone angle to full width at half-maximum intensity of the dominant vector field component does not exceed 60x00B0;. The highest accuracy field distributions to date of the less familiar higher-order Hermitex2013;Gaussian vector components are also presented. Hermitex2013;Gaussian E-B vectors only approximately satisfy Maxwellx2019;s equations. We have defined a Maxwellx2019;s-residual power measure to quantify the approximation quality of different vector sets, and each set approximately (or exactly) satisfies Maxwellx2019;s equations. Several vectorial x201C;applications,x201D; i.e., research fields that involve vector laser beams, are briefly discussed. The mathematics of vectorial Gaussian beams is particularly applicable to the analysis of the physical systems associated with such applications. Two user-friendly x201C;Mathematicax201D; programs, one for computing six high-accuracy vector components of a Hermitex2013;Gaussian beam, and the other for computing the six practically Maxwellx2019;s-equations-satisfying components of a focused laser beam, supplement this review.

  • Device-independent certification of one-shot distillable entanglement

    Arnon-Friedman R. & Bancal J. (2019) New Journal of Physics.
    Entanglement sources that produce many entangled states act as a main component in applications exploiting quantum physics such as quantum communication and cryptography. Realistic sources are inherently noisy, cannot run for an infinitely long time, and do not necessarily behave in an independent and identically distributed manner. An important question then arises-how can one test, or certify, that a realistic source produces high amounts of entanglement? Crucially, a meaningful and operational solution should allow us to certify the entanglement which is available for further applications after performing the test itself (in contrast to assuming the availability of an additional source which can produce more entangled states, identical to those which were tested). To answer the above question and lower bound the amount of entanglement produced by an uncharacterised source, we present a protocol that can be run by interacting classically with uncharacterised (but not entangled to one another) measurement devices used to measure the states produced by the source. A successful run of the protocol implies that the remaining quantum state has high amounts of one-shot distillable entanglement. That is, one can distill many maximally entangled states out of the single remaining state. Importantly, our protocol can tolerate noise and, thus, certify entanglement produced by realistic sources. With the above properties, the protocol acts as the first 'operational device-independent entanglement certification protocol' and allows one to test and benchmark uncharacterised entanglement sources which may be otherwise incomparable.

  • Power narrowing: counteracting Doppler broadening in two-color transitions

    Finkelstein R., Lahad O., Michel O., Davidson O., Poem E. & Firstenberg O. (2019) New Journal of Physics.
    Doppler broadening in thermal ensembles degrades the absorption cross-section and the coherence time of collective excitations. In two photon transitions, it is common to assume that this problem becomes worse with larger wavelength mismatch. Here we identify an opposite mechanism, where such wavelength mismatch leads to cancellation of Doppler broadening via the counteracting effects of velocity-dependent light-shifts and Doppler shifts. We show that this effect is general, common to both absorption and transparency resonances, and favorably scales with wavelength mismatch. We experimentally confirm the enhancement of transitions for different low-lying orbitals in rubidium atoms and use calculations to extrapolate to high-lying Rydberg orbitals. These calculations predict a dramatic enhancement of up to 20-fold increase in absorption, even in the presence of large homogeneous broadening. More general configurations, where an auxiliary dressing field is used to counteract Doppler broadening, are also discussed and experimentally demonstrated. The mechanism we study can be applied as well for rephasing of spin waves and increasing the coherence time of quantum memories.

  • Precision Measurement of Atomic Isotope Shifts Using a Two-Isotope Entangled State

    Manovitz T., Shaniv R., Shapira Y., Ozeri R. & Akerman N. (2019) Physical Review Letters.
    Atomic isotope shifts (ISs) are the isotope-dependent energy differences between atomic electron energy levels. These shifts have an important role in atomic and nuclear physics, and have been recently suggested as unique probes of physics beyond the standard model under the condition that they are determined significantly more precisely than the current state of the art. In this Letter, we present a simple and robust method for measuring ISs by taking advantage of Hilbert subspaces that are insensitive to common-mode noise yet sensitive to the IS. Using this method we evaluate the IS of the 5S(1/2) 4D(5/2) transition between Sr-86(+) and Sr-88(+) with a 1.6 x 10(-11) relative uncertainty to be 570 264 063.435(5)(8) (statistical)(systematic) Hz. Furthermore, we detect a relative difference of 3.46(23) x 10(-8) between the orbital g factors of the electrons in the 4D(5/2) level of the two isotopes. Our method is relatively easy to implement and is indifferent to element or isotope, paving the way for future tabletop searches for new physics, posing interesting prospects for testing quantum many-body calculations, and for the study of nuclear structure.

  • Shaping electron-hole trajectories for solid-state high harmonic generation control

    Orenstein G., Uzan A. J., Gadasi S., Arusi-Parpar T., Krüger M., Cireasa R., Bruner B. D. & Dudovich N. (2019) Optics Express.
    Solid-state high-harmonic generation (HHG) by an intense infra-red (IR) laser field offers a new route to generate coherent attosecond light pulses in the extreme ultraviolet regime. The propagation of the IR driving field in the dense solid medium is accompanied by non-linear processes which shape the generating waveform. In this work, we introduce a monolithic scheme in which we both exploit the non-linear propagation to manipulate a two color driving field, as well as generate high harmonics within a single crystal. We show that the resulting non-commensurate, bi-chromatic, generating field provides precise control over the periodicity of the HHG process. This control enables us to manipulate the spectral positions of the discrete harmonic peaks. Our method advances solid-state HHG spectroscopy, and offers a simple route towards tunable, robust XUV sources.

  • Band Gap Engineering Improves the Efficiency of Double Quantum Dot Upconversion Nanocrystals

    Yang G., Meir N., Raanan D. & Oron D. (2019) Advanced Functional Materials.
    Solution-processed core/multishell semiconductor quantum dots (QDs) could be tailored to facilitate the carrier separation, promotion, and recombination mechanisms necessary to implement photon upconversion. In contrast to other upconversion schemes, upconverting QDs combine the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. Nevertheless, their upconversion quantum yield (UCQY) is fairly low. Here, design rules are uncovered that enable to significantly enhance the performance of double QD upconversion systems, and these findings are leveraged to fabricate upconverting QDs with increased photon upconversion efficiency and reduced saturation intensities under pulsed excitation. The role of the intra-QD band alignment is exemplified by comparing the upconversion process in PbS/CdS/ZnSe QDs with that of PbS/CdS/CdSe ones with variable CdSe shell thicknesses. It is shown that electron delocalization into the shell leads to a longer-lived intermediate state in the QDs, facilitating further absorption of photons, and enhancing the upconversion process. The performance of these upconversion QDs under pulsed excitation versus continuous pumping is also compared; the reasons for the significant differences between these two regimes are discussed. The results show how one can overcome some of the limitations of previous upconverting QDs, with potential applications in biophotonics and infrared detection.

  • Phase stability transfer across the optical domain using a commercial optical frequency comb system

    Peleg L., Akerman N., Manovitz T., Alon M. & Ozeri R. (2019) arXiv.
    We report the frequency noise suppression of a 674nm diode laser by phase-locking it to a 1560nm cavity-stabilized laser, using a commercial optical frequency comb. By phase-locking the frequency comb to the narrow reference at telecom wavelength we were able to phase-coherently distribute the reference stability across the optical spectrum. Subsequently, we used one of the comb teeth as an optical reference for a 674nm external cavity diode laser. We demonstrated the locked 674nm laser frequency stability by comparing it to an independent cavity-stabilized laser of the same wavelength and by performing spectroscopic measurements on a dipole-forbidden narrow optical transition in a single $^{88}$Sr$^+$ ion. These measurements indicated a fast laser linewidth of 19Hz and 16Hz, respectively.

  • Electron wavefunctions probed by all-optical attosecond interferometry

    Kruger M., Azoury D., Kneller O., Rozen S., Bruner B. D., Clergerie A., Fabre B., Pons B., Mairesse Y. & Dudovich N. (2019) .
    Photoelectron spectroscopy is a powerful method that provides insight into the quantum mechanical properties of a wide range of systems. The ionized electron wavefunction carries information on the structure of the bound orbital, the ionic potential as well as the photo-ionization dynamics itself. While photoelectron spectroscopy resolves the absolute amplitude of the wavefunction, retrieving the spectral phase information has been a long-standing challenge. Established photo-ionization spectroscopy methods, such as reconstruction of attosecond beating by interference of two-photon transitions (RABBITT), are able to access only the first derivative of the spectral phase, the group delay, due to their nonlinear nature [1,2]. Here, we transfer the electron phase retrieval problem into an optical one by measuring the time-reversed process of photo-ionization - photo-recombination - in high-harmonic generation (HHG). The extreme-ultraviolet attosecond pulses produced in HHG carry the full information of the light-matter interaction, including the electronic structure of the system under scrutiny. Their spectral phase directly encodes the photo-ionization dipole phase due to the final step of HHG - photo-recombination of a well-defined electron wavepacket into the ion. In this work, we access this phase using interferometry, which is highly challenging in the XUV spectral domain due to the absence of efficient optics.

  • NIR-to-visible upconversion in quantum dots via a ligand induced charge transfer state

    Meir N., Pinkas I. & Oron D. (2019) RSC Advances.
    Nanomaterials that possess the ability to upconvert two low-energy photons into a single high-energy photon are of great potential to be useful in a variety of applications. Recent attempts to realize upconversion (UC) in semiconducting quantum dot (QD) systems focused mainly on fabrication of heterostructured colloidal double QDs, or by using colloidal QDs as sensitizers for triplet-triplet annihilation in organic molecules. Here we propose a simplified approach, in which colloidal QDs are coupled to organic thiol ligands and UC is achieved via a charge-transfer state at the molecule-dot interface. We synthesized core/shell CdSe/CdS QDs and replaced their native ligands with thiophenol molecules. The alignment of the molecular HOMO with respect to the QD conduction band resulted in the formation of a new charge-transfer transition from which UC can be promoted. We performed a series of pump-probe experiments and proved the non-linear emission exhibited by these QDs is the result of UC by sequential photon absorption, and further characterized the QD-ligand energy landscape by transient absorption. Finally, we demonstrate that this scheme can also be applied in a QD solid.

  • Band alignment and charge transfer in CsPbBr<sub>3</sub>-CdSe nanoplatelet hybrids coupled by molecular linkers

    Dey S., Cohen H., Pinkas I., Lin H., Kazes M. & Oron D. (2019) Journal of Chemical Physics.
    Formation of a p-n junction-like with a large built-in field is demonstrated at the nanoscale, using two types of semiconducting nanoparticles, CsPbBr<sub>3</sub> nanocrystals and CdSe nanoplatelets, capped with molecular linkers. By exploiting chemical recognition of the capping molecules, the two types of nanoparticles are brought into mutual contact, thus initiating spontaneous charge transfer and the formation of a strong junction field. Depending on the choice of capping molecules, the magnitude of the latter field is shown to vary in a broad range, corresponding to an interface potential step as large as ∼1 eV. The band diagram of the system as well as the emergence of photoinduced charge transfer processes across the interface is studied here by means of optical and photoelectron based spectroscopies. Our results propose an interesting template for generating and harnessing internal built-in fields in heterogeneous nanocrystal solids.

  • Higher-Order Photon Correlation as a Tool To Study Exciton Dynamics in Quasi-2D Nanoplatelets

    Amgar D., Yang G., Tenne R. & Oron D. (2019) Nano Letters.
    Colloidal semiconductor nanoplatelets, in which carriers are strongly confined only along one dimension, present fundamentally different excitonic properties than quantum dots, which support strong confinement in all three dimensions. In particular, multiple excitons strongly confined in just one dimension are free to rearrange in the lateral plane, reducing the probability for multibody collisions. Thus, while simultaneous multiple photon emission is typically quenched in quantum dots, in nanoplatelets its probability can be tuned according to size and shape. Here, we focus on analyzing multiexciton dynamics in individual CdSe/CdS nanoplatelets of various sizes through the measurement of second-, third-, and fourth-order photon correlations. For the first time, we can directly probe the dynamics of the two, three, and four exciton states at the single nanocrystal level. Remarkably, although higher orders of correlation vary substantially among the synthesis products, they strongly correlate with the value of second order antibunching. The scaling of the higher-order moments with the degree of antibunching presents a small yet clear deviation from the accepted model of Auger recombination through binary collisions. Such a deviation suggests that many-body contributions are present already at the level of triexcitons. These findings highlight the benefit of high-order photon correlation spectroscopy as a technique to study multiexciton dynamics in colloidal semiconductor nanocrystals.

  • Coherent diffusion of partial spatial coherence

    Chriki R., Smartsev S., Eger D., Firstenberg O. & Davidson N. (2019) Optica.
    Partially coherent fields are abundant in many physical systems. While the propagation of partially coherent light undergoing diffraction is well understood, its evolution in the presence of coherent diffusion (i.e., diffusion of complex fields) remains largely unknown. Here we develop an analytic model describing the diffusion of partially coherent beams and study it experimentally. Our model is based on a diffusion analog of the famous Van Cittert–Zernike theorem. Experimentally, we use a four-wave mixing scheme with electromagnetically induced transparency to couple optical speckle patterns to diffusing atoms in a warm vapor. The spatial coherence properties of the speckle fields are monitored under diffusion and are compared to our model and to the familiar evolution of spatial coherence of light speckles under diffraction. We identify several important differences between the evolution dynamics of the spatial coherence under diffraction and diffusion. Our findings shed light on the propagation of partially coherent fields in media where multiple scattering or thermal motion lead to coherent diffusion.

  • Shaping of a laser-accelerated proton beam for radiobiology applications via genetic algorithm

    Cavallone M., Flacco A. & Malka V. (2019) Physica Medica-European Journal Of Medical Physics.
    Laser-accelerated protons have a great potential for innovative experiments in radiation biology due to the sub-picosecond pulse duration and high dose rate achievable. However, the broad angular divergence makes them not optimal for applications with stringent requirements on dose homogeneity and total flux at the irradiated target. The strategy otherwise adopted to increase the homogeneity is to increase the distance between the source and the irradiation plane or to spread the beam with flat scattering systems or through the transport system itself. Such methods considerably reduce the proton flux and are not optimal for laser-accelerated protons. In this paper we demonstrate the use of a Genetic Algorithm (GA) to design an optimal non-flat scattering system to shape the beam and efficiently flatten the transversal dose distribution at the irradiated target. The system is placed in the magnetic transport system to take advantage of the presence of chromatic focusing elements to further mix the proton trajectories. The effect of a flat scattering system placed after the transport system is also presented for comparison. The general structure of the GA and its application to the shaping of a laser-accelerated proton beam are presented, as well as its application to the optimisation of dose distribution in a water target in air.

  • Complex lasers with controllable coherence

    Cao H., Chriki R., Bittner S., Friesem A. A. & Davidson N. (2019) Nature Reviews Physics.
    Lasers have enabled scientific and technological progress, owing to their high brightness and high coherence. However, the high spatial coherence of laser illumination is not always desirable, because it can cause adverse artefacts such as speckle noise. To reduce spatial coherence, new laser cavity geometries and alternative feedback mechanisms have been developed. By tailoring the spatial and spectral properties of cavity resonances, the number of lasing modes, the emission profiles and the coherence properties can be controlled. In this Technical Review, we present an overview of such unconventional, complex lasers, with a focus on their spatial coherence properties. Laser coherence control not only provides an efficient means for eliminating coherent artefacts but also enables new applications in imaging and wavefront shaping. High spatial coherence of laser illumination is not always desirable, because it can cause adverse artefacts such as speckle noise. This Technical Review describes unconventional lasers that have inherently low and/or tunable spatial coherence. Key pointsHigh spatial coherence of laser emission, a common feature of conventional lasers, causes deleterious effects, including speckle noise and crosstalk, in applications such as full-field imaging, display, materials processing, photolithography, holography and optical trapping.Fundamental changes in laser design or operation are more effective than schemes to reduce the spatial coherence outside of the laser cavity to achieve low or tunable spatial coherence.Random lasers and wave-chaotic microcavity lasers support numerous lasing modes with distinct spatial profiles, producing emission of low spatial coherence suitable for speckle-free, full-field imaging and spatial coherence gating.The number of modes and thus spatial coherence of degenerate cavity laser emission can be tuned with little change in power, allowing fast switching between speckle-free imaging and speckle-contrast imaging.Wavefront shaping inside a degenerate cavity laser can generate propagation-invariant output beams or spin-dependent twisted light beams. The dynamic wavefront control can focus laser light through a random scattering medium.

  • Simple and Tight Device-Independent Security Proofs

    Arnon-Friedman R., Renner R. & Vidick T. (2019) SIAM Journal on Computing.
    Device-independent security is the gold standard for quantum cryptography: not only is security based entirely on the laws of quantum mechanics, but it holds irrespective of any a priori assumptions on the quantum devices used in a protocol, making it particularly applicable in a quantum-wary environment. While the existence of device-independent protocols for tasks such as randomness expansion and quantum key distribution has recently been established, the underlying proofs of security remain very challenging, yield rather poor key rates, and demand very high quality quantum devices, thus making them all but impossible to implement in practice. We introduce a technique for the analysis of device-independent cryptographic protocols. We provide a flexible protocol and give a security proof that provides quantitative bounds that are asymptotically tight, even in the presence of general quantum adversaries. At a high level our approach amounts to establishing a reduction to the scenario in which the untrusted device operates in an identical and independent way in each round of the protocol. This is achieved by leveraging the sequential nature of the protocol and makes use of a newly developed tool, the "entropy accumulation theorem" of Dupuis, Fawzi, and Renner [Entropy Accumulation, preprint, 2016]. As concrete applications we give simple and modular security proofs for device-independent quantum key distribution and randomness expansion protocols based on the CHSH inequality. For both tasks, we establish essentially optimal asymptotic key rates and noise tolerance. In view of recent experimental progress, which has culminated in loophole-free Bell tests, it is likely that these protocols can be practically implemented in the near future.

  • Quantum interface for noble-gas spins

    Katz O., Shaham R. & Firstenberg O. (2019) arXiv.
    An ensemble of noble-gas nuclear spins is a unique quantum system that could maintain coherence for many hours at room temperature and above, owing to exceptional isolation from the environment. This isolation, however, is a mixed blessing, limiting the ability of these ensembles to coherently interface with other quantum systems. Here we show that spin-exchange collisions with alkali-metal atoms render a quantum interface for noble-gas spins without impeding their long coherence times. We formulate the many-body theory of the hybrid system and reveal a collective mechanism that strongly couples the macroscopic quantum states of the two spin ensembles. Despite their stochastic and random nature, weak collisions enable entanglement and reversible exchange of nonclassical excitations in an efficient, controllable, and deterministic process. We outline feasible parameters for reaching the strong-coupling regime, paving the way towards an experimental realization of hour-long quantum memories and entanglement at room-temperature.

  • A Nanoscopic View of Photoinduced Charge Transfer in Organic Nanocrystalline Heterojunctions

    Zhang Q., Cohen S. R., Rosenhek-Goldian I., Amgar D., Bar-Elli O., Tsarfati Y., Bendikov T., Shimon L. J. W., Feldman Y., Iron M. A., Weissman H., Levine I., Oron D. & Rybtchinski B. (2019) Journal of Physical Chemistry C.
    Organic photovoltaics enable cost-efficient, tunable, and flexible platforms for solar energy conversion, yet their performance and stability are still far from optimal. Here, we present a study of photoinduced charge transfer processes between electron donor and acceptor organic nanocrystals as part of a pathfinding effort to develop robust and efficient organic nanocrystalline materials for photovoltaic applications. For this purpose, we utilized nanocrystals of perylenediimides as the electron acceptors and nanocrystalline copper phthalocyanine as the electron donor. Three different configurations of donor-acceptor heterojunctions were prepared. Charge transfer in the heterojunctions was studied with Kelvin probe force microscopy under laser or white light excitation. Moreover, detailed morphology characterizations and time-resolved photoluminescence measurements were conducted to understand the differences in the photovoltaic processes of these organic nanocrystals. Our work demonstrates that excitonic properties can be tuned by controlling the crystal and interface structures in the nanocrystalline heterojunctions, leading to a minimization of photovoltaic losses.

  • State-selective coherent motional excitation as a new approach for the manipulation, spectroscopy and state-to-state chemistry of single molecular ions

    Meir Z., Hegi G., Najafian K., Sinhal M. & Willitsch S. (2019) Faraday Discussions.
    We present theoretical and experimental progress towards a new approach for the precision spectroscopy, coherent manipulation and state-to-state chemistry of single isolated molecular ions in the gas phase. Our method uses a molecular beam for creating packets of rotationally cold neutrals from which a single molecule is state-selectively ionized and trapped inside a radiofrequency ion trap. In addition to the molecular ion, a single co-trapped atomic ion is used to cool the molecular external degrees of freedom to the ground state of the trap and to detect the molecular state using state-selective coherent motional excitation from a modulated optical-dipole force acting on the molecule. We present a detailed discussion and theoretical characterization of the present approach. We simulate the molecular signal experimentally using a single atomic ion, indicating that different rovibronic molecular states can be resolved and individually detected with our method. The present approach for the coherent control and non-destructive detection of the quantum state of a single molecular ion opens up new perspectives for precision spectroscopies relevant for, e.g., tests of fundamental physical theories and the development of new types of clocks based on molecular vibrational transitions. It will also enable the observation and control of chemical reactions of single particles on the quantum level. While focusing on N2+ as a prototypical example in the present work, our method is applicable to a wide range of diatomic and polyatomic molecules.

  • Observation of Stimulated Hawking Radiation in an Optical Analogue

    Drori J., Rosenberg Y., Bermudez D., Silberberg Y. & Leonhardt U. (2019) Physical Review Letters.
    The theory of Hawking radiation can be tested in laboratory analogues of black holes. We use light pulses in nonlinear fiber optics to establish artificial event horizons. Each pulse generates a moving perturbation of the refractive index via the Kerr effect. Probe light perceives this as an event horizon when its group velocity, slowed down by the perturbation, matches the speed of the pulse. We have observed in our experiment that the probe stimulates Hawking radiation, which occurs in a regime of extreme nonlinear fiber optics where positive and negative frequencies mix.

  • Temperature Control in Dissipative Cavities by Entangled Dimers

    Dag C. B., Niedenzu W., Ozaydin F., Mustecaplioglu O. E. & Kurizki G. (2019) Journal of Physical Chemistry C.
    We show that the temperature of a cavity field can be drastically varied by its interaction with suitably entangled atom pairs (dimers) traversing the cavity under realistic atomic decoherence. To this end we resort to the hitherto untapped resource of naturally entangled dimers whose state can be simply controlled via molecular dissociation, collisions forming the dimer, or unstable dimers such as positronium. Depending on the chosen state of the dimer, the cavity-field mode can be driven to a steady-state temperature that is either much lower or much higher than the ambient temperature, despite adverse effects of cavity loss and atomic decoherence. Entangled dimers enable much broader range of cavity temperature control than single "phaseonium" atoms with coherently superposed levels. Such dimers are shown to constitute highly caloric fuel that can ensure high efficiency or power in photonic thermal engines. Alternatively, they can serve as controllable thermal baths for quantum simulation of energy exchange in photosynthesis or quantum annealing.

  • Resonant Faraday effect using high-order harmonics for the investigation of ultrafast demagnetization

    Alves C., Lambert G., Malka V., Hehn M., Malinowski G., Hennes M., Chardonnet V., Jal E., Luning J. & Vodungbo B. (2019) Physical Review B.
    During the past few years high-order harmonic generation (HHG) has opened up the field of ultrafast spectroscopy to an ever larger community by providing a table-top and affordable femtosecond extreme ultraviolet (EUV) and soft-x-ray source. In particular, the field of femtomagnetism has largely benefited from the development of these sources. However, the use of x-ray magnetic circular dichroism (XMCD) as a probe of magnetization, the most versatile and reliable one, has been constrained by the lack of polarization control at HHG sources, so studies have relied on more specific magneto-optical effects. Even the recent developments on the generation of elliptically polarized harmonics have only resulted in a few time-resolved experiments relying on this powerful technique since they add complexity to already-difficult measurements. In this article we show how to easily probe magnetization dynamics with linearly polarized EUV or soft-x-ray light with a versatility similar to XMCD by exploiting the Faraday effect. Static and time-resolved measurements of the Faraday effect are presented around the Co M edges. Using simple theoretical considerations, we show how to retrieve the samples magnetization dynamics from the Faraday rotation and ellipticity transients. Ultrafast demagnetization dynamics of a few nanometers in Co-based samples are measured with this method in out-of-plane as well as in-plane magnetization configurations, showing its great potential for the study of femtomagnetism.

  • An Excellent Modifier: Carbon Quantum Dots for Highly Efficient Carbon-Electrode-Based Methylammonium Lead Iodide Solar Cells

    Han J., Zhou Y., Yin X., Nan H., Tai M., Gu Y., Li J., Oron D. & Lin H. (2019) Solar Energy Materials and Solar Cells.
    Low-temperature paintable carbon-electrode-based perovskite solar cells (LC-PSCs) are developed predominantly due to several significant advantages of carbon electrodes: they do not require a hole transport layer (HTL) and are low-cost, easy to fabricate on a large scale, and possess high ambient stability. The most critical hindrance to the photovoltaic performance of LC-PSCs is the inferior contact between the perovskite and carbon layers. Herein, carbon quantum dots (CQDs) as interface modifiers between the perovskite layer and carbon electrode are applied, which can facilitate hole injection into the carbon electrode, thus improving the photovoltaic performance of LC-PSCs. Meanwhile, the crystalline properties and hole mobility of the perovskite layer are improved significantly, and defect states in the perovskite layer are passivated following the embedding of CQDs. Finally, a champion efficiency of 13.3% in LC-PSCs based on perovskite-CQDs hybrid films without HTL is achieved for an active area of 1 cm(2), which represents a 24.3% improvement over the pristine device. Furthermore, LC-PSC devices maintain more than 95% of their initial efficiency under demanding conditions (humidity >40%, 1000 h). This work opens up a promising pathway to improve the photovoltaic performance of LC-PSCs and potentially also of other thin-film solar cells.

  • The Role of Electron Trajectories in XUV-Initiated High-Harmonic Generation

    Krueger M., Azoury D., Bruner B. D. & Dudovich N. (2019) Applied Sciences (Switzerland).
    High-harmonic generation spectroscopy is a powerful tool for ultrafast spectroscopy with intrinsic attosecond time resolution. Its major limitation-the fact that a strong infrared driving pulse is governing the entire generation process-is lifted by extreme ultraviolet (XUV)-initiated high-harmonic generation (HHG). Tunneling ionization is replaced by XUV photoionization, which decouples ionization from recollision. Here we probe the intensity dependence of XUV-initiated HHG and observe strong spectral frequency shifts of the high harmonics. We are able to tune the shift by controlling the instantaneous intensity of the infrared field. We directly access the reciprocal intensity parameter associated with the electron trajectories and identify short and long trajectories. Our findings are supported and analyzed by ab initio calculations and a semiclassical trajectory model. The ability to isolate and control long trajectories in XUV-initiated HHG increases the range of the intrinsic attosecond clock for spectroscopic applications.

  • Two-layer Gaussian-based MCTDH study of the S1 ← S0 vibronic absorption spectrum of formaldehyde using multiplicative neural network potentials

    Koch W., Bonfanti M., Eisenbrandt P., Nandi A., Fu B., Bowman J., Tannor D. & Burghardt I. (2019) Journal of Chemical Physics.
    The absorption spectrum of the vibronically allowed S1(1A2) ← S0(1A1) transition of formaldehyde is computed by combining multiplicative neural network (NN) potential surface fits, based on multireference electronic structure data, with the two-layer Gaussian-based multiconfiguration time-dependent Hartree (2L-GMCTDH) method. The NN potential surface fit avoids the local harmonic approximation for the evaluation of the potential energy matrix elements. Importantly, the NN surface can be constructed so as to be physically well-behaved outside the domain spanned by the ab initio data points. A comparison with experimental results shows spectroscopic accuracy of the converged surface and 2L-GMCTDH quantum dynamics.

  • Quadrupole Shift Cancellation Using Dynamic Decoupling

    Shaniv R., Akerman N., Manovitz T., Shapira Y. & Ozeri R. (2019) Physical Review Letters.
    We present a method that uses radio-frequency pulses to cancel the quadrupole shift in optical clock transitions. Quadrupole shifts are an inherent inhomogeneous broadening mechanism in trapped ion crystals and impose one of the limitations forcing current optical ion clocks to work with a single probe ion. Canceling this shift, at each interrogation cycle of the ion frequency, reduces the complexity in using N > 1 ions in clocks, thus allowing for a reduction of the instability in the clock frequency by root N according to the standard quantum limit. Our sequence relies on the tensorial nature of the quadrupole shift, and thus also cancels other tensorial shifts, such as the tensor ac stark shift. We experimentally demonstrate our sequence on three and seven Sr-88(+) ions trapped in a linear Paul trap, using correlation spectroscopy. We show a reduction of the quadrupole shift difference between ions to the approximate to 10 mHz level where other shifts, such as the relativistic second-order Doppler shift, are expected to limit our spectral resolution. In addition, we show that using radio-frequency dynamic decoupling we can also cancel the effect of first-order Zeeman shifts.

  • Interferometric attosecond lock-in measurement of extreme-ultraviolet circular dichroism

    Azoury D., Kneller O., Kruger M., Bruner B. D., Cohen O., Mairesse Y. & Dudovich N. (2019) Nature Photonics.
    Probing the vectorial properties of light-matter interactions inherently requires control over the polarization state of light. The generation of extreme-ultraviolet attosecond pulses has opened new perspectives in measurements of chiral phenomena. However, limited polarization control in this regime prevents the development of advanced vectorial measurement schemes. Here, we establish an extreme-ultraviolet lock-in detection scheme, allowing the isolation and amplification of extremely weak chiral signals, by achieving dynamical polarization control. We demonstrate a time-domain approach to control and modulate the polarization state, and perform its characterization via an in situ measurement. Our approach is based on the collinear superposition of two independent, phase-locked, orthogonally polarized extreme-ultraviolet sources and the control of their relative delay with sub-cycle accuracy. We achieve lock-in detection of magnetic circular dichroism, transferring weak amplitude variations into a phase modulation. This approach holds the potential to significantly extend the scope of vectorial measurements to the attosecond and nanometre frontiers.

  • Optimizing the Nonlinear Optical Response of Plasmonic Metasurfaces

    Blechman Y., Almeida E., Sain B. & Prior Y. (2019) Nano Letters.
    Controlling the nonlinear optical response of nano scale metamaterials opens new exciting applications such as frequency conversion or flat metal optical elements. To utilize the already well-developed fabrication methods, a systematic design methodology for obtaining high nonlinearities is required. In this paper we consider an optimization-based approach, combining a multiparameter genetic algorithm with three-dimensional finite-difference time domain (FDTD) simulations. We investigate two choices of the optimization function: one which looks for plasmonic resonance enhancements at the frequencies of the process using linear FDTD, and another one, based on nonlinear FDTD, which directly computes the predicted nonlinear response. We optimize a four-wave-mixing process with specific predefined input frequencies in an array of rectangular nanocavities milled in a thin free-standing gold film. Both approaches yield a significant enhancement of the nonlinear signal. Although the direct calculation gives rise to the maximum possible signal, the linear optimization provides the expected triply resonant configuration with almost the same enhancement, while being much easier to implement in practice.

  • Electronic wavefunctions probed by all-optical attosecond interferometry

    Azoury D., Kneller O., Rozen S., Bruner B. D., Clergerie A., Mairesse Y., Fabre B., Pons B., Dudovich N. & Kruger M. (2019) Nature Photonics.
    In photoelectron spectroscopy, the ionized electron wavefunction carries information about the structure of the bound orbital and the ionic potential as well as about the photoionization dynamics. However, retrieving the quantum phase information has been a long-standing challenge. Here, we transfer the electron phase retrieval problem into an optical one by measuring the time-reversed process of photoionization-photo-recombination-in attosecond pulse generation. We demonstrate all-optical interferometry of two independent phase-locked attosecond light sources. This measurement enables us to directly determine the phase shift associated with electron scattering in simple quantum systems such as helium and neon, over a large energy range. Moreover, the strong-field nature of attosecond pulse generation resolves the dipole phase around the Cooper minimum in argon through a single scattering angle. This method may enable the probing of complex orbital phases in molecular systems as well as electron correlations through resonances subject to strong laser fields.

  • Terahertz coherent anti-Stokes Raman scattering microscopy

    Ren L., Hurwitz I., Raanan D., Oulevey P., Oron D. & Silberberg Y. (2019) Optica.
    Vibrational spectroscopic imaging is useful and important in biological and medical studies. Yet, vibrational imaging in the terahertz region (

  • Controlled Enantioselective Orientation of Chiral Molecules with an Optical Centrifuge

    Milner A. A., Fordyce J. A. M., MacPhail-Bartley I., Wasserman W., Milner V., Tutunnikov I. & Averbukh I. S. (2019) Physical Review Letters.
    We report on the first experimental demonstration of enantioselective rotational control of chiral molecules with a laser field. In our experiments, two enantiomers of propylene oxide are brought to accelerated unidirectional rotation by means of an optical centrifuge. Using Coulomb explosion imaging, we show that the centrifuged molecules acquire preferential orientation perpendicular to the plane of rotation, and that the direction of this orientation depends on the relative handedness of the enantiomer and the rotating centrifuge field. The observed effect is in agreement with theoretical predictions and is reproduced in numerical simulations of the centrifuge excitation followed by Coulomb explosion of the centrifuged molecules. The demonstrated technique opens new avenues in optical enantioselective control of chiral molecules with a plethora of potential applications in differentiation, separation, and purification of chiral mixtures.

  • Axiparabola: a long-focal-depth, high-resolution mirror for broadband high-intensity lasers

    Smartsev S., Caizergues C., Oubrerie K., Gautier J., Goddet J., Tafzi A., Kim Ta Phuoc, Malka V. & Thaury C. (2019) Optics Letters.
    Diffraction puts a fundamental limit on the distance over which a light beam can remain focused. For about 30 years, several techniques to overcome this limit have been demonstrated. Here, we propose a reflective optics, namely, the axiparabola, that allows to extend the production of “diffraction-free” beams to high-peak-power and broadband laser pulses. We first describe the properties of this aspheric optics. We then analyze and compare its performances in numerical simulations and in experiments. Finally, we use it to produce a plasma waveguide that can guide an intense laser pulse over 10 millimeters.

  • Rapid laser solver for the phase retrieval problem

    Tradonsky C., Gershenzon I., Pal V., Chriki R., Friesem A. A., Raz O. & Davidson N. (2019) Science Advances.
    Tailored physical systems were recently exploited to rapidly solve hard computational challenges, such as spin simulators, combinatorial optimization, and focusing through scattering media. Here, we address the phase retrieval problem where an object is reconstructed from its scattered intensity distribution. This is a key problem in many applications, ranging from x-ray imaging to astrophysics, and currently, it lacks efficient direct reconstruction methods: The widely used indirect iterative algorithms are inherently slow. We present an optical approach based on a digital degenerate cavity laser, whose most probable lasing mode rapidly and efficiently reconstructs the object. Our experimental results suggest that the gain competition between the many lasing modes acts as a highly parallel computer that could rapidly solve the phase retrieval problem. Our approach applies to most two-dimensional objects with known compact support, including complex-valued objects, and can be generalized to imaging through scattering media and other hard computational tasks.

  • Flat-top laser beams over an extended range

    Reddy A. N. K., Pal V., Mahler S., Friesem A. A. & Davidson N. (2019) Journal of Physics: Conference Series.
    Designs based on single diffractive-optical-elements for obtaining flat-top laser intensity distributions that remain constant over a long range during free-space propagation are presented. Flat-top beams with different orders n exhibit a different range of propagation. For various working distances z, the resulting flat-top beam yields a different depth of focus. By controlling spectral properties of laser distributions, it is possible to maintain invariant flat-top intensity distributions for relatively long propagation distances.

  • Are quantum thermodynamic machines better than their classical counterparts?

    Ghosh A., Mukherjee V., Niedenzu W. & Kurizki G. (2019) European Physical Journal-Special Topics.
    Interesting effects arise in cyclic machines where both heat and ergotropy transfer take place between the energising bath and the system (the working fluid). Such effects correspond to unconventional decompositions of energy exchange between the bath and the system into heat and work, respectively, resulting in efficiency bounds that may surpass the Carnot efficiency. However, these effects are not directly linked with quantumness, but rather with heat and ergotropy, the likes of which can be realised without resorting to quantum mechanics.

  • Ratiometric widefield imaging with spectrally balanced detection

    Yudovich S., Shani L., Grupi A., Bar-Elli O., Steinitz D., Oron D. & Weiss S. (2019) Biomedical Optics Express.
    Ratiometric imaging is an invaluable tool for quantitative microscopy, allowing for robust detection of FRET, anisotropy, and spectral shifts of nano-scale optical probes in response to local physical and chemical variations such as local pH, ion composition, and electric potential. In this paper, we propose and demonstrate a scheme for widefield ratiometric imaging that allows for continuous tuning of the cutoff wavelength between its two spectral channels. This scheme is based on angle-tuning the image splitting dichroic beamsplitter, similar to previous works on tunable interference filters. This configuration allows for ratiometric imaging of spectrally heterogeneous samples, which require spectral tunability of the detection path in order to achieve good spectrally balanced ratiometric detection.

  • Simplified approach to low-frequency coherent anti-Stokes Raman spectroscopy using a sharp spectral edge filter

    Ren L., Asher M., Yaffe O., Silberberg Y. & Oron D. (2019) Optics Letters.
    Coherent anti-Stokes Raman scattering (CARS) has found wide applications in biomedical research. Compared with alternatives, single-beam CARS is especially attractive at low frequencies. Yet, currently existing schemes necessitate a relatively complicated setup to perform high-resolution spectroscopy. Here we show that the spectral sharp edge formed by an ultra-steep long-pass filter is sufficient for performing CARS spectroscopy, simplifying the system significantly. We compare the sensitivity of the presented methodology with available counterparts both theoretically and experimentally. Importantly, we show that this method, to the best of our knowledge, is the simplest and most suitable for vibrational imaging and spectroscopy in the very low-frequency regime (

  • Colloidal Mercury-Doped CdSe Nanoplatelets with Dual Fluorescence

    Galle T., Kazes M., Huebner R., Lox J., Khoshkhoo M. S., Sonntag L., Tietze R., Sayevich V., Oron D., Koitzsch A., Lesnyak V. & Eychmueller A. (2019) Chemistry of Materials.
    Quasi-two-dimensional (2D) CdSe nanoplatelets (NPLs) are distinguished by their unique optical properties in comparison to classical semiconductor nano crystals, such as extremely narrow emission line widths, reduced Auger recombination, and relatively high absorption cross sections. Inherent to their anisotropic 2D structure, however, is the loss of continuous tunability of their photoluminescence (PL) properties due to stepwise growth. On top of that, limited experimental availability of NPLs of different thicknesses and ultimately the bulk band gap of CdSe constrain the achievable PL wavelengths. Here, we report on the doping of CdSe NPLs with mercury, which gives rise to additional PL in the red region of the visible spectrum and in the near-infrared region. We employ a seeded-growth method with injection solutions containing cadmium, selenium, and mercury. The resulting NPLs retain their anisotropic structure, are uniform in size and shape, and present significantly altered spectroscopic characteristics due to the existence of additional energetic states. We conclude that doping takes place by employing elemental analysis in combination with PL excitation spectroscopy, X-ray photoelectron spectroscopy, and single particle fluorescence spectroscopy, confirming single emitters being responsible for multiple distinct emission signals.

  • Quantized refrigerator for an atomic cloud

    Niedenzu W., Mazets I., Kurizki G. & Jendrzejewski F. (2019) Quantum Chaos.
    We propose to implement a quantized thermal machine based on a mixture of two atomic species. One atomic species implements the working medium and the other implements two (cold and hot) baths. We show that such a setup can be employed for the refrigeration of a large bosonic cloud starting above and ending below the condensation threshold. We analyze its operation in a regime conforming to the quantized Otto cycle and discuss the prospects for continuous-cycle operation, addressing the experimental as well as theoretical limitations. Beyond its applicative significance, this setup has a potential for the study of fundamental questions of quantum thermodynamics.

  • Rotational Echoes as a Tool for Investigating Ultrafast Collisional Dynamics of Molecules

    Zhang H., Lavorel B., Billard F., Hartmann J. -., Hertz E., Faucher O., Ma J., Wu J., Gershnabel E., Prior Y. & Averbukh I. S. (2019) Physical Review Letters.
    We show that recently discovered rotational echoes of molecules provide an efficient tool for studying collisional molecular dynamics in high-pressure gases. Our study demonstrates that rotational echoes enable the observation of extremely fast collisional dissipation, at timescales of the order of a few picoseconds, and possibly shorter. The decay of the rotational alignment echoes in CO2 gas and CO2-He mixture up to 50 bar was studied experimentally, delivering collision rates that are in good agreement with the theoretical expectations. The suggested measurement protocol may be used in other high-density media, and potentially in liquids.

  • Challenges and opportunities in attosecond and XFEL science

    Lindroth E., Calegari F., Young L., Harmand M., Dudovich N., Berrah N. & Smirnova O. (2019) Nature Reviews Physics.
    Seven scientists share their views on some of the latest developments in attosecond science and X-ray free electron lasers (XFELs) and highlight exciting new directions.

  • Resonant Hawking radiation as an instability

    Bermudez D. & Leonhardt U. (2019) Classical and Quantum Gravity.
    We consider a simple model for a black-hole laser: a Bose-Einstein condensate with uniform speed of sound and partially uniform flow, establishing two horizons, a black-hole and a white-hole horizon. Waves confined between the horizons are amplified similar to radiation in a laser cavity. Black-hole lasing appears as an instability with discrete sets of modes given approximately by a round-trip condition. We found that, in addition to the regular Hawking radiation, trans-Planckian radiation does tunnel out of the black-hole laser.

  • Laser-induced persistent orientation of chiral molecules

    Tutunnikov I., Floss J., Gershnabel E., Brumer P. & Averbukh I. S. (2019) Physical Review A.
    We study, both classically and quantum mechanically, enantioselective orientation of gas-phase chiral molecules excited by laser fields with twisted polarization. Counterintuitively, the induced orientation, whose direction is laser controllable, does not disappear after the excitation but stays long after the end of the laser pulses. We computationally demonstrate this long-lasting orientation, using propylene oxide molecules (CH3CHCH2O, or PPO) as an example, and consider two kinds of fields with twisted polarization: a pair of delayed cross-polarized pulses and an optical centrifuge. This chiral effect opens avenues for detecting molecular chirality, measuring enantiomeric excess, and separating enantiomers with the help of inhomogeneous external fields.

  • Lifshitz theory of the cosmological constant

    Leonhardt U. (2019) Annals of Physics.
    Astrophysics has given empirical evidence for the cosmological constant that accelerates the expansion of the universe. Atomic, Molecular, and Optical Physics have proven experimentally that the quantum vacuum exerts forces - the van der Waals and Casimir forces - on neutral matter. It has long been conjectured (Zel'dovich, 1968) that the two empirical facts, the cosmological constant and the Casimir force, have a common theoretical explanation, but all attempts of deriving both from a unified theory in quantitative detail have not been successful so far. In AMO Physics, Lifshitz theory has been the standard theoretical tool for describing the measured forces of the quantum vacuum. This paper develops a version of Lifshitz theory that also accounts for the electromagnetic contribution to the cosmological constant. Assuming that the other fields of the Standard Model behave similarly, gives a possible quantum-optical explanation for what has been called dark energy. 

  • Quantum optical two-atom thermal diode

    Kargi C., Naseem M. T., Opatrny T., Mustecaplioglu O. E. & Kurizki G. (2019) Physical Review E.
    We put forward a quantum-optical model for a thermal diode based on heat transfer between two thermal baths through a pair of interacting qubits. We find that if the qubits are coupled by a Raman field that induces an anisotropic interaction, heat flow can become nonreciprocal and undergoes rectification even if the baths produce equal dissipation rates of the qubits, and these qubits can be identical, i.e., mutually resonant. The heat flow rectification is explained by four-wave mixing and Raman transitions between dressed states of the interacting qubits and is governed by a global master equation. The anisotropic two-qubit interaction is the key to the operation of this simple quantum thermal diode, whose resonant operation allows for high-efficiency rectification of large heat currents. Effects of spatial overlap of the baths are addressed. We discuss the possible realizations of the model in various platforms, including optomechanical setups, systems of trapped ions, and circuit QED.

  • Collectively enhanced thermalization via multiqubit collisions

    Manatuly A., Niedenzu W., Roman-Ancheyta R., Cakmak B., Mustecaplioglu O. E. & Kurizki G. (2019) Physical Review. E.
    We investigate the evolution of a target qubit caused by its multiple random collisions with N-qubit clusters. Depending on the cluster state, the evolution of the target qubit may correspond to its effective interaction with a thermal bath, a coherent (laser) drive, or a squeezed bath. In cases where the target qubit relaxes to a thermal state, its dynamics can exhibit a quantum advantage, whereby the target-qubit temperature can be scaled up proportionally to N-2 and the thermalization time can be shortened by a similar factor, provided the appropriate coherence in the cluster is prepared by nonthermal means. We dub these effects quantum superthermalization because of the analogies to superradiance. Experimental realizations of these effects are suggested.

  • Quantum image scanning microscopy: concept and considerations towards applicability

    Tenne R., Rossman U., Rephael B., Israel Y., Krupinski-Ptaszek A., Lapkiewicz R., Silberberg Y. & Oron D. (2019) .
    Technological advancements in the creation, manipulation and detection of quantum states of light have motivated the application of such states to overcome classical limits in sensing and imaging. In particular, there has been a surge of recent interest in super-resolution imaging based on principles of quantum optics. However, the application of such schemes for practical imaging of biological samples is demanding in terms of signal-to-noise ratio, speed of acquisition and robustness with respect to sample labeling. Here, we re-introduce the concept of quantum image scanning microscopy (Q-ISM), a super-resolution method that enhances the classical image scanning microscopy (ISM) method by measuring photon correlations. Q-ISM was already utilized to achieve super-resolved images of a biological sample labeled with fluorescent nanoscrystals whose contrast is based entirely on a quantum optical phenomenon, photon antibunching. We present here an experimental demonstration of the method and discuss with further details its prospects for application in life science microscopy.

  • Light focusing through scattering media via linear fluorescence variance maximization, and its application for fluorescence imaging

    Daniel A., Oron D. & Silberberg Y. (2019) Optics Express.
    We demonstrate focusing and imaging through a scattering medium without access to the fluorescent object by using wavefront shaping. Our concept is based on utilizing the spatial fluorescence contrast which naturally exists in the hidden target object. By scanning the angle of incidence of the illuminating laser beam and maximizing the variation of the detected fluorescence signal from the object, as measured by a bucket detector at the front of the scattering medium, we are able to generate a tightly focused excitation spot. Thereafter, an image is obtained by scanning the focus over the object within the memory effect range. The requirements for applicability of the method and the comparison with speckle-correlation based focusing methods are discussed. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

  • Fast dose fractionation using ultra-short laser accelerated proton pulses can increase cancer cell mortality, which relies on functional PARP1 protein

    Bayart E., Flacco A., Delmas O., Pommarel L., Levy D., Cayallone M., Megnin-Chanet F., Deutsch E. & Malka V. A. (2019) Scientific Reports.
    Radiotherapy is a cornerstone of cancer management. The improvement of spatial dose distribution in the tumor volume by minimizing the dose deposited in the healthy tissues have been a major concern during the last decades. Temporal aspects of dose deposition are yet to be investigated. Laser-plasma-based particle accelerators are able to emit pulsed-proton beams at extremely high peak dose rates (~10 <sup>9</sup> Gy/s) during several nanoseconds. The impact of such dose rates on resistant glioblastoma cell lines, SF763 and U87-MG, was compared to conventionally accelerated protons and X-rays. No difference was observed in DNA double-strand breaks generation and cells killing. The variation of the repetition rate of the proton bunches produced an oscillation of the radio-induced cell susceptibility in human colon carcinoma HCT116 cells, which appeared to be related to the presence of the PARP1 protein and an efficient parylation process. Interestingly, when laser-driven proton bunches were applied at 0.5 Hz, survival of the radioresistant HCT116 p53 <sup>−/−</sup> cells equaled that of its radiosensitive counterpart, HCT116 WT, which was also similar to cells treated with the PARP1 inhibitor Olaparib. Altogether, these results suggest that the application modality of ultrashort bunches of particles could provide a great therapeutic potential in radiotherapy.

  • Super-resolution enhancement by quantum image scanning microscopy

    Tenne R., Rossman U., Rephael B., Israel Y., Krupinski-Ptaszek A., Lapkiewicz R., Silberberg Y. & Oron D. (2019) Nature Photonics.
    The principles of quantum optics have yielded a plethora of ideas to surpass the classical limitations of sensitivity and resolution in optical microscopy. While some ideas have been applied in proof-of-principle experiments, imaging a biological sample has remained challenging, mainly due to the inherently weak signal measured and the fragility of quantum states of light. In principle, however, these quantum protocols can add new information without sacrificing the classical information and can therefore enhance the capabilities of existing super-resolution techniques. Image scanning microscopy, a recent addition to the family of super-resolution methods, generates a robust resolution enhancement without reducing the signal level. Here, we introduce quantum image scanning microscopy: combining image scanning microscopy with the measurement of quantum photon correlation allows increasing the resolution of image scanning microscopy up to twofold, four times beyond the diffraction limit. We introduce the Q-ISM principle and obtain super-resolved optical images of a biological sample stained with fluores-cent quantum dots using photon antibunching, a quantum effect, as a resolution-enhancing contrast mechanism.

  • Collective motion of an atom array under laser illumination

    Shahmoon E., Lukin M. D. & Yelin S. F. (2019) .
    We develop a theoretical formalism for the study of light-induced motion of atoms trapped in a two-dimensional (2D) array, considering the effect of multiple scattering of light between the atoms. We find that the atomic motion can be described by a collective diffusion equation, wherein laser-induced dipole–dipole forces couple the motion of different atoms. This coupling leads to the formation of collective mechanical modes of the array atoms, whose spatial structure and stability depend on the parameters of the illuminating laser and the geometry of the 2D array. We demonstrate the application of our formalism for the analysis of light-induced heating of the 2D array. The presented approach should be useful for treating the optomechanical properties of recently proposed quantum optical platforms made of atomic arrays.

  • Optical properties of spherulite opals

    Yallapragada V. J. & Oron D. (2019) Optics Letters.
    Spherulites are birefringent structures with spherical symmetry, typically observed in crystallized polymers. We compute the band structure of opals made of close-packed assemblies of highly birefringent spherulites. We demonstrate that spherulitic birefringence of constituent spheres does not affect the symmetries of an opal, yet significantly affects the dispersion of eigenmodes, leading to new pseudogaps in sections of the band structure and, consequently, enhanced reflectivity. 

  • Two-stage laser acceleration of high quality protons using a tailored density plasma

    Wan Y., Andriyash I. A., Hua J. F., Pai C., Lu W., Mori W. B., Joshi C. & Malka V. (2019) Physical Review Accelerators and Beams.
    A new scheme for a laser-driven proton accelerator based on a sharply tailored near-critical-density plasma target is proposed. The designed plasma profile allows for the laser channeling of the dense plasma, which triggers a two-stage acceleration of protons-first accelerated by the laser acting as a snowplow in plasma, and then by the collisionless shock launched from the sharp density downramp. Thanks to laser channeling in the near-critical plasma, the formed shock is radially small and collimated. This allows it to generate a significant space-charge field, which acts as a monochromator, defocusing the lower energy protons while the highest ones remain collimated. Our theoretical and numerical analysis demonstrates production of high-energy proton beams with few tens of percent energy spread, few degrees divergence angle and charge up to few nC. With a PW-class ultrashort laser this scheme predicts the generation of such high quality proton beams with energies up to several hundreds of MeV.

  • Tunable High Spatio-Spectral Purity Undulator Radiation from a Transported Laser Plasma Accelerated Electron Beam

    Ghaith A., Oumbarek D., Roussel E., Corde S., Labat M., Andre T., Loulergue A., Andriyash I. A., Chubar O., Kononenko O., Smartsev S., Marcouille O., Kitegi C., Marteau F., Valleau M., Thaury C., Gautier J., Sebban S., Tafzi A., Blache F., Briquez F., Tavakoli K., Carcy A., Bouvet F., Dietrich Y., Lambert G., Hubert N., El Ajjouri M., Polack F., Dennetiere D., Leclercq N., Rommeluere P., Duval J. -., Sebdaoui M., Bourgoin C., Lestrade A., Benabderrahmane C., Veteran J., Berteaud P., De Oliveira C., Goddet J. P., Herbeaux C., Szwaj C., Bielawski S., Malka V. & Couprie M. -. (2019) Scientific Reports.
    Undulator based synchrotron light sources and Free Electron Lasers (FELs) are valuable modern probes of matter with high temporal and spatial resolution. Laser Plasma Accelerators (LPAs), delivering GeV electron beams in few centimeters, are good candidates for future compact light sources. However the barriers set by the large energy spread, divergence and shot-to-shot fluctuations require a specific transport line, to shape the electron beam phase space for achieving ultrashort undulator synchrotron radiation suitable for users and even for achieving FEL amplification. Proof-of-principle LPA based undulator emission, with strong electron focusing or transport, does not yet exhibit the full specific radiation properties. We report on the generation of undulator radiation with an LPA beam based manipulation in a dedicated transport line with versatile properties. After evidencing the specific spatio-spectral signature, we tune the resonant wavelength within 200–300 nm by modification of the electron beam energy and the undulator field. We achieve a wavelength stability of 2.6%. We demonstrate that we can control the spatio-spectral purity and spectral brightness by reducing the energy range inside the chicane. We have also observed the second harmonic emission of the undulator.

  • Improving techniques for diagnostics of laser pulses by compact representations

    Sidorenko P., Dikopoltsev A., Zahavy T., Lahav O., Gazit S., Shechtman Y., Szameit A., Tannor D. J., Eldar Y. C., Segev M. & Cohen O. (2019) Optics Express.
    We propose and demonstrate, numerically and experimentally, use of sparsity as prior information for extending the capabilities and performance of techniques and devices for laser pulse diagnostics. We apply the concept of sparsity in three different applications. First, we improve a photodiode-oscilloscope system’s resolution for measuring the intensity structure of laser pulses. Second, we demonstrate the intensity profile reconstruction of ultrashort laser pulses from intensity autocorrelation measurements. Finally, we use a sparse representation of pulses (amplitudes and phases) to retrieve measured pulses from incomplete spectrograms of cross-correlation frequency-resolved optical gating traces.

  • Simple route to enhancement of soft X-ray high harmonic generation sources

    Bruner B. D., Arusi-Parpar T., Kruger M. & Dudovich N. (2019) .
    Soft x-ray sources based on laser-driven high-harmonic generation (HHG) offer a tabletop alternative to sources generated at synchrotron and free-electron laser facilities [1,2]. In this work we demonstrate two orders of magnitude enhancement in conversion efficiency of HHG soft x-rays. The enhancement occurs on a single particle level and is based upon sub-optical-cycle control and enhancement of the tunnelling ionization rate [3]. Using a simple two-colour synthesizer to drive HHG, here we show that both high enhancement and high HHG flux can be achieved in the soft x-ray (SXR) region. In the presented results, the enhancement spans over a 250 eV bandwidth with pulse energies reaching the pJ level.

  • Measuring magnetic fields with magnetic field insensitive transitions

    Shapira Y., Dallal Y., Ozeri R. & Stern A. (2019) Physical Review Letters.
    Atomic sensing is, at large, based on measuring energy differences. Specifically, magnetometry is typically performed by using a superposition of two quantum states, the energy difference of which depends linearly on the magnetic field due to the Zeeman effect. The magnetic field is then evaluated from repeated measurements of the accumulated dynamic phase between the two Zeeman states. Here we show that atomic clock states, with an energy separation that is independent of the magnetic field, can nevertheless acquire a phase that is magnetic field dependent. We experimentally demonstrate this on an ensemble of optically trapped Rb87 atoms. Finally, we use this effect to propose a magnetic field sensing method for static and time-dependent magnetic fields and analyze its sensitivity, showing it essentially allows for high-sensitivity magnetometery.

  • HHG probing of atomic dipoles by electronic wave-packet caustics

    Facciala D., Pabst S., Bruner B. D., Ciriolo A. G., Devetta M., Negro M., Soifer H., Dudovich N., Stagira S. & Vozzi C. (2019) XXI INTERNATIONAL CONFERENCE ON ULTRAFAST PHENOMENA 2018 (UP 2018).
    We exploit high-order harmonic generation spectroscopy at the caustics of the recombining electron wave-packet as a method for directly comparing experimental spectra with ab-initio theories. Experimental results in xenon and comparison with ab-initio time-dependent configuration-interaction singles calculations allowed to assess the role of the wave-packet enhancement during the giant resonance. Results in argon show that this technique can also be applied to other targets.

  • Multiport Atom Interferometry for Inertial Sensing

    Yankelev D., Avinadav C., Davidson N. & Firstenberg O. (2019) Physical Review A.
    We present techniques for inertial-sensing atom interferometers which produce multiple phase measurements per experimental cycle. With these techniques, we realize two types of multiport measurements, namely, quadrature phase detection and real-time systematic phase cancellation, which address challenges in operating high-sensitivity cold-atom sensors in mobile and field applications. We confirm experimentally the increase in sensitivity due to quadrature phase detection in the presence of large phase uncertainty, and demonstrate suppression of systematic phases on a single-shot basis.

  • Two-Dimensional Maxwell Fisheye for Integrated Optics

    Bitton O., Bruch R. & Leonhardt U. (2018) Physical Review Applied.
    Maxwell invented a refractive-index profile where light goes in circles and every point is focused. A device with such a profile is called the Maxwell fisheye and it is an absolute optical instrument: it has the ability to collect all rays from any emitting source and recombine them in phase at the corresponding focal point inside the device. Absolute optical instruments may find diverse applications if they can be made in integrated optics on a silicon chip for infrared light. We have fabricated the Maxwell fisheye in silicon photonics and have demonstrated its focusing properties. Our fabrication technique can also be applied to the manufacturing of other devices where smooth and sharp structures need to be made in one lithography step.

  • Quasi-monoenergetic multi-GeV electron acceleration by optimizing the spatial and spectral phases of PW laser pulses

    Shin J., Kim H. T., Pathak V. B., Hojbota C., Lee S. K., Sung J. H., Lee H. W., Yoon J. W., Jeon C., Nakajima K., Sylla F., Lifschitz A., Guillaume E., Thaury C., Malka V. & Nam C. H. (2018) Plasma Physics and Controlled Fusion.
    Generation of high-quality electron beams from laser wakefield acceleration requires optimization of initial experimental parameters. We present here the dependence of accelerated electron beams on the temporal profile of a driving PW laser, the density, and length of an interacting medium. We have optimized the initial parameters to obtain 2.8 GeV quasi-monoenergetic electrons which can be applied further to the development of compact electron accelerators and radiations sources.

  • Spin-controlled twisted laser beams: intra-cavity multi-tasking geometric phase metasurfaces

    Chriki R., Maguid E., Tradonsky C., Kleiner V., Friesem A. A., Davidson N. & Hasman E. (2018) Optics Express.
    Novel multi-tasking geometric phase metasurfaces were incorporated into a modified degenerate cavity laser as an output coupler to efficiently generate spin-dependent twisted light beams of different topologies. Multiple harmonic scalar vortex laser beams were formed by replacing the laser output coupler with a shared-aperture metasurface. A variety of distinct wave functions were obtained with an interleaving approach - random interspersing of geometric phase profiles within shared-aperture metasurfaces. Utilizing the interleaved metasurfaces, we generated vectorial vortices by coherently superposing of scalar vortices with opposite topological charges and spin states. We also generated multiple partially coherent vortices by incorporating harmonic response metasurfaces. The incorporation of the metasurface platforms into a laser cavity opens a pathway to novel types of nanophotonic functionalities and enhanced light-matter interactions, offering exciting new opportunities for light manipulation. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

  • Cooperative many-body enhancement of quantum thermal machine power

    Niedenzu W. & Kurizki G. (2018) New Journal of Physics.
    We study the impact of cooperative many-body effects on the operation of periodically-driven quantum thermal machines, particularly heat engines and refrigerators. In suitable geometries, N two-level atoms can exchange energy with the driving field and the (hot and cold) thermal baths at a faster rate than a single atom due to their SU(2) symmetry that causes the atoms to behave as a collective spin-N/2 particle. This cooperative effect boosts the power output of heat engines compared to the power output of N independent, incoherent, heat engines. In the refrigeration regime, similar cooling-power boost takes place.

  • Control of ellipticity in high-order harmonic generation driven by two linearly polarized fields

    Mahieu B., Stremoukhov S., Gauthier D., Spezzani C., Alves C., Vodungbo B., Zeitoun P., Malka V., De Ninno G. & Lambert G. (2018) Physical Review A.
    We demonstrate experimentally the control of the polarization (ellipticity and polarization axis) of femtosecond high-order harmonics. The method relies on a two-color (ω - 2ω) configuration, where both ω and 2ω generating fields have linear polarizations with a variable crossing angle. We correlate our measurements with the conservation rules of energy and linear momentum accounting for harmonic generation in a two-color field. We evidence that the generation process, and especially the number of ω and 2ω photons absorbed for generating a given harmonic, strongly depends on the crossing angle. Finally, relying on a simple formalism, we derive analytical formulæ for calculating both polarization axis and ellipticity of the separate harmonics. The model corroborates our results and represents a base for future investigations.

  • Toward Heisenberg-Limited Rabi Spectroscopy

    Shaniv R., Manovitz T., Shapira Y., Akerman N. & Ozeri R. (2018) Physical Review Letters.
    The use of entangled states was shown to improve the fundamental limits of spectroscopy to beyond the standard-quantum limit. Here, rather than probing the free evolution of the phase of an entangled state with respect to a local oscillator, we probe the evolution of an initially separable two-atom register under an Ising spin Hamiltonian with a transverse field. The resulting correlated spin-rotation spectrum is twice as narrow as that of an uncorrelated rotation. We implement this ideally Heisenberg-limited Rabi spectroscopy scheme on the optical-clock electric-quadrupole transition of Sr-88(+) using a two-ion crystal. We further show that depending on the initial state, correlated rotation can occur in two orthogonal subspaces of the full Hilbert space, yielding entanglement-enhanced spectroscopy of either the average transition frequency of the two ions or their difference from the mean frequency. The use of correlated spin rotations can potentially lead to new paths for clock stability improvement.

  • Producing an efficient, collimated, and thin annular beam with a binary axicon

    Livneh O., Afek G. & Davidson N. (2018) Applied Optics.
    We propose and demonstrate a method to produce a thin and highly collimated annular beam that propagates similarly to an ideal thin Gaussian ring beam, maintaining its excellent propagation properties. Our optical configuration is composed of a binary axicon, a circular binary phase grating, and a lens, making it robust and well suited for high-power lasers. It has a near-perfect circular profile with a dark center, and its large radius to waist ratio is achieved with high conversion efficiency. The measured profile and propagation are in excellent agreement with a numerical Fourier simulation we perform. (C) 2018 Optical Society of America

  • Robust Entanglement Gates for Trapped-Ion Qubits

    Shapira Y., Shaniv R., Manovitz T., Akerman N. & Ozeri R. (2018) Physical Review Letters.
    High-fidelity two-qubit entangling gates play an important role in many quantum information processing tasks and are a necessary building block for constructing a universal quantum computer. Such high-fidelity gates have been demonstrated on trapped-ion qubits; however, control errors and noise in gate parameters may still lead to reduced fidelity. Here we propose and demonstrate a general family of two-qubit entangling gates which are robust to different sources of noise and control errors. These gates generalize the renowned Molmer-Sorensen gate by using multitone drives. We experimentally implemented several of the proposed gates on Sr-88(+) ions trapped in a linear Paul trap and verified their resilience.

  • Topologically Controlled Intracavity Laser Modes Based on Pancharatnam-Berry Phase

    Maguid E., Chriki R., Yannai M., Kleiner V., Hasman E., Friesem A. A. & Davidson N. (2018) ACS Photonics.
    Incorporation of a metasurface that involves spin-orbit interaction phenomenon into a laser cavity provides a route to the generation of spin-controlled intracavity modes with different topologies. By utilizing the geometric phase, Pancharatnam-Berry phase, we found a spin-enabled self-consistent cavity solution of a Nd:YAG laser with a silicon-based metasurface. Using this solution we generated a laser mode possessing spin-controlled orbital-angular momentum. Moreover, an experimental demonstration of a vectorial vortex is achieved by the coherent superposition of modes with opposite spin and orbital angular momenta. We experimentally achieved a high mode purity of 95% due to laser mode competition and purification. The photonic spin-orbit interaction mechanism within a laser-cavity can be implemented with multifunctional shared aperture nanoantenna arrays to achieve multiple intracavity topologies.

  • Rapid Voltage Sensing with Single Nanorods via the Quantum Confined Stark Effect

    Bar-Elli O., Steinitz D., Yang G., Tenne R., Ludwig A., Kuo Y., Triller A., Weiss S. & Oron D. (2018) ACS Photonics.
    Properly designed colloidal semiconductor quantum dots (QDs) have already been shown to exhibit high sensitivity to external electric fields via the quantum confined Stark effect (QCSE). Yet, detection of the characteristic spectral shifts associated with the effect of the QCSE has traditionally been painstakingly slow, dramatically limiting the sensitivity of these QD sensors to fast transients. We experimentally demonstrate a new detection scheme designed to achieve shot-noise-limited sensitivity to emission wavelength shifts in QDs, showing feasibility for their use as local electric field sensors on the millisecond time scale. This regime of operation is already potentially suitable for detection of single action potentials in neurons at a high spatial resolution.

  • High-order harmonic generation spectroscopy by recolliding electron caustics

    Facciala D., Pabst S., Bruner B. D., Ciriolo A. G., Devetta M., Negro M., Geetha P. P., Pusala A., Soifer H., Dudovich N., Stagira S. & Vozzi C. (2018) JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS.
    Spectral focusing of the recolliding electron in high-order harmonic generation driven by two-color fields is shown to be a powerful tool for isolating and enhancing hidden spectral features of the target under study. In previous works we used this technique for probing multi-electron effects in xenon and we compared our experimental results with time-dependent configuration-interaction singles calculations. We demonstrate here that this technique can be exploited for reconstructing the enhancement factor of the xenon giant dipole resonance and we discuss the sensitivity of this method to macroscopic effects. We then extend the technique to argon in order to test the applicability of this procedure to other targets.

  • Control of laser plasma accelerated electrons for light sources

    Andre T., Andriyash I. A., Loulergue A., Labat M., Roussel E., Ghaith A., Khojoyan M., Thaury C., Valleau M., Briquez F., Marteau F., Tavakoli K., N'Gotta P., Dietrich Y., Lambert G., Malka V., Benabderrahmane C., Veteran J., Chapuis L., El Ajjouri T., Sebdaoui M., Hubert N., Marcouille O., Berteaud P., Leclercq N., El Ajjouri M., Rommeluere P., Bouvet F., Duval J. -., Kitegi C., Blache F., Mahieu B., Corde S., Gautier J., Ta Phuoc K., Goddet J. P., Lestrade A., Herbeaux C., Evain C., Szwaj C., Bielawski S., Tafzi A., Rousseau P., Smartsev S., Polack F., Dennetiere D., Bourassin-Bouchet C., De Oliveira C. & Couprie M. -. (2018) Nature Communications.
    With gigaelectron-volts per centimetre energy gains and femtosecond electron beams, laser wakefield acceleration (LWFA) is a promising candidate for applications, such as ultrafast electron diffraction, multistaged colliders and radiation sources (betatron, compton, undulator, free electron laser). However, for some of these applications, the beam performance, for example, energy spread, divergence and shot-to-shot fluctuations, need a drastic improvement. Here, we show that, using a dedicated transport line, we can mitigate these initial weaknesses. We demonstrate that we can manipulate the beam longitudinal and transverse phase-space of the presently available LWFA beams. Indeed, we separately correct orbit mis-steerings and minimise dispersion thanks to specially designed variable strength quadrupoles, and select the useful energy range passing through a slit in a magnetic chicane. Therefore, this matched electron beam leads to the successful observation of undulator synchrotron radiation after an 8m transport path. These results pave the way to applications demanding in terms of beam quality.

  • Fast, noise-free memory for photon synchronization at room temperature

    Poem E., Finkelstein R., Michel O., Lahad O. & Firstenberg O. (2018) .
    Future quantum photonic networks require coherent optical memories for synchronizing quantum sources and gates of probabilistic nature. Room temperature operation is also desirable for ease of scaling up. Until now, however, room-temperature atomic memories have suffered from an intrinsic read-out noise due to spontaneous four-wave-mixing. Here we demonstrate a new scheme for storing photons at room temperature, the fast ladder memory (FLAME). In this scheme, stimulated two-photon absorption is used instead of the previously used stimulated Raman scattering. As here the competing spontaneous processes would require spontaneous absorption of an optical photon, rather than emission, the noise is greatly suppressed. Furthermore, high external efficiency can be achieved as the control is well separated in frequency from the signal, and could be filtered out using highly efficient interference filters. We run the protocol in rubidium vapour, both on and off single-photon resonance, demonstrating a ratio of 50 between storage time and signal pulse width, an external total efficiency of over 25%, and only 2.3 × 10 <sup>-4</sup> noise photons per extracted signal photon. This paves the way towards the efficient synchronization of probabilistic gates and sources at room temperature, and the controlled production of large quantum states of light.

  • Rapid and efficient formation of propagation invariant shaped laser beams

    Chriki R., Barach G., Tradosnky C., Smartsev S., Pal V., Friesem A. A. & Davidson N. (2018) Optics Express.
    A rapid and efficient all-optical method for forming propagation invariant shaped beams by exploiting the optical feedback of a laser cavity is presented. The method is based on the modified degenerate cavity laser (MDCL), which is a highly incoherent cavity laser. The MDCL has a very large number of degrees of freedom (320,000 modes in our system) that can be coupled and controlled, and allows direct access to both the real space and Fourier space of the laser beam. By inserting amplitude masks into the cavity, constraints can be imposed on the laser in order to obtain minimal loss solutions that would optimally lead to a superposition of Bessel-Gauss beams forming a desired shaped beam. The resulting beam maintains its transverse intensity distribution for relatively long propagation distances. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

  • Casimir self-stress in a dielectric sphere

    Avni Y. & Leonhardt U. (2018) Annals of Physics.
    The dielectric sphere has been an important test case for understanding and calculating the vacuum force of a dielectric body onto itself. Here we develop a method for computing this force in homogeneous spheres of arbitrary dielectric properties embedded in arbitrary homogeneous backgrounds, assuming only that both materials are isotropic and dispersionless. Our results agree with known special cases; most notably we reproduce the prediction of Boyer and Schwinger et al. of a repulsive Casimir force of a perfectly reflecting shell. Our results disagree with the literature in the dilute limit. We argue that the Casimir self-stress cannot be regarded as due to pair-wise Casimir–Polder interactions, but rather due to reflections of virtual electromagnetic waves.

  • Fast, Noise-Free Memory for Photon Synchronization at Room Temperature

    Poem E., Finkelstein R., Michel O., Lahad O. & Firstenberg O. (2018) .
    Future quantum photonic networks require coherent optical memories for synchronizing quantum sources and gates of probabilistic nature. Room temperature operation is also desirable for ease of scaling up. Until now, however, room-temperature atomic memories have suffered from an intrinsic read-out noise due to spontaneous four-wave-mixing. Here we demonstrate a new scheme for storing photons at room temperature, the fast ladder memory (FLAME). In this scheme, stimulated two-photon absorption is used instead of the previously used stimulated Raman scattering. As here the competing spontaneous processes would require spontaneous absorption of an optical photon, rather than emission, the noise is greatly suppressed. Furthermore, high external efficiency can be achieved as the control is well separated in frequency from the signal, and could be filtered out using highly efficient interference filters. We run the protocol in rubidium vapour, both on and off single-photon resonance, demonstrating a ratio of 50 between storage time and signal pulse width, an external total efficiency of over 25%, and only 2.3x10(-4) noise photons per extracted signal photon. This paves the way towards the efficient synchronization of probabilistic gates and sources at room temperature, and the controlled production of large quantum states of light.

  • Optically functional isoxanthopterin crystals in the mirrored eyes of decapod crustaceans

    Palmer B. A., Hirsch A., Brumfeld V., Aflalo E. D., Pinkas I., Sagi A., Rosenne S., Oron D., Leiserowitz L., Kronik L., Weiner S. & Addadi L. (2018) Proceedings of the National Academy of Sciences of the United States of America.
    The eyes of some aquatic animals form images through reflective optics. Shrimp, lobsters, crayfish, and prawns possess reflecting superposition compound eyes, composed of thousands of square-faceted eye units (ommatidia). Mirrors in the upper part of the eye (the distal mirror) reflect light collected from many ommatidia onto the photosensitive elements of the retina, the rhabdoms. A second reflector, the tapetum, underlying the retina, back-scatters dispersed light onto the rhabdoms. Using microCT and cryo-SEM imaging accompanied by in situ micro-X-ray diffraction and micro-Raman spectroscopy, we investigated the hierarchical organization and materials properties of the reflective systems at high resolution and under close-to-physiological conditions. We show that the distal mirror consists of three or four layers of plate-like nanocrystals. The tapetum is a diffuse reflector composed of hollow nanoparticles constructed from concentric lamellae of crystals. Isoxanthopterin, a pteridine analog of guanine, forms both the reflectors in the distal mirror and in the tapetum. The crystal structure of isoxanthopterin was determined from crystal-structure prediction calculations and verified by comparison with experimental X-ray diffraction. The extended hydrogen-bonded layers of the molecules result in an extremely high calculated refractive index in the H-bonded plane, n = 1.96, which makes isoxanthopterin crystals an ideal reflecting material. The crystal structure of isoxanthopterin, together with a detailed knowledge of the reflector superstructures, provide a rationalization of the reflective optics of the crustacean eye.

  • Robust enhancement of high harmonic generation via attosecond control of ionization

    Bruner B. D., Kruger M., Pedatzur O., Orenstein G., Azoury D. & Dudovich N. (2018) Optics Express.
    High-harmonic generation (HHG) is a powerful tool to generate coherent attosecond light pulses in the extreme ultraviolet. However, the low conversion efficiency of HHG at the single atom level poses a significant practical limitation for many applications. Enhancing the efficiency of the process defines one of the primary challenges in the application of HHG as an advanced XUV source. In this work, we demonstrate a new mechanism, which in contrast to current methods, enhances the HHG conversion efficiency purely on a single particle level. We show that using a bichromatic driving field, sub-optical-cycle control and enhancement of the tunnelling ionization rate can be achieved, leading to enhancements in HHG efficiency by up to two orders of magnitude. Our method advances the perspectives of HHG spectroscopy, where isolating the single particle response is an essential component, and offers a simple route toward scalable, robust XUV sources. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

  • High-Brilliance Betatron γ -Ray Source Powered by Laser-Accelerated Electrons

    Ferri J., Corde S., Dopp A., Lifschitz A., Doche A., Thaury C., Phuoc K. T., Mahieu B., Andriyash I. A., Malka V. A. & Davoine X. (2018) Physical Review Letters.
    Recent progress in laser-driven plasma acceleration now enables the acceleration of electrons to several gigaelectronvolts. Taking advantage of these novel accelerators, ultrashort, compact, and spatially coherent x-ray sources called betatron radiation have been developed and applied to high-resolution imaging. However, the scope of the betatron sources is limited by a low energy efficiency and a photon energy in the 10 s of kiloelectronvolt range, which for example prohibits the use of these sources for probing dense matter. Here, based on three-dimensional particle-in-cell simulations, we propose an original hybrid scheme that combines a low-density laser-driven plasma accelerator with a high-density beam-driven plasma radiator, thereby considerably increasing the photon energy and the radiated energy of the betatron source. The energy efficiency is also greatly improved, with about 1% of the laser energy transferred to the radiation, and the γ-ray photon energy exceeds the megaelectronvolt range when using a 15 J laser pulse. This high-brilliance hybrid betatron source opens the way to a wide range of applications requiring MeV photons, such as the production of medical isotopes with photonuclear reactions, radiography of dense objects in the defense or industrial domains, and imaging in nuclear physics.

  • Roadmap on transformation optics

    McCall M., Pendry J. B., Galdi V., Lai Y., Horsley S. A. R., Li J., Zhu J., Mitchell-Thomas R. C., Quevedo-Teruel O., Tassin P., Ginis V., Martini E., Minatti G., Maci S., Ebrahimpouri M., Hao Y., Kinsler P., Gratus J., Lukens J. M., Weiner A. M., Leonhardt U., Smolyaninov I. I., Smolyaninova V. N., Thompson R. T., Wegener M., Kadic M. & Cummer S. A. (2018) Journal of Optics.
    Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues.Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.

  • Mode conversion via wavefront shaping

    Daniel A., Song X. B., Oron D. & Silberberg Y. (2018) Optics Express.
    In recent years, wavefront shaping has been utilized to control and correct distorted light for enhancing a bright spot, generation of a Bessel beam or darkening a complete area at the output of a scattering system. All these outcomes can be thought of as enhancing a particular mode of the output field. In this letter, we study the relation between the attainable enhancement factor, corresponding to the efficiency of mode conversion, and the field distribution of the target mode. Working in the limit of a thin diffuser enables not only a comparison between experimental and simulated results, but also allows for derivation of an analytic formula. These results shed light on the ability to use a scattering medium as a mode converter and on the relationship between the desired shape and the efficiency. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

  • Fast, noise-free memory for photon synchronization at room temperature

    Poem E., Finkelstein R., Michel O., Lahad O. & Firstenberg O. (2018) .
    Future quantum photonic networks require coherent optical memories, preferably operating at room temperature, for synchronizing quantum sources and gates of probabilistic nature. Until now, however, room-temperature atomic memories have suffered from an intrinsic read-out noise. Here we demonstrate a fast ladder memory (FLAME) mapping the optical field onto the superposition between electronic orbitals of rubidium vapor. Employing a ladder level-system of orbital transitions with nearly degenerate frequencies simultaneously enables high bandwidth, low noise, and long memory lifetime. We store and retrieve 1.7-ns-long pulses, containing 0.5 photons on average, and observe short-time external efficiency of 25%, memory lifetime (1/e) of 86 ns, and below 10 <sup>-4</sup> added noise photons. Consequently, coupling this memory to a probabilistic source would enhance the on-demand photon generation probability by a factor of 12, the highest number yet reported for a noise-free, room-temperature memory. This paves the way towards the controlled production of large quantum states of light from probabilistic photon sources.

  • Orienting Asymmetric Molecules by Laser Fields with Twisted Polarization

    Gershnabel E. & Averbukh I. S. (2018) Physical Review Letters.
    We study interaction of generic asymmetric molecules with laser fields having twisted polarization, using a pair of strong time-delayed short laser pulses with crossed linear polarizations as an example. We show that such an excitation not only provides unidirectional rotation of the most polarizable molecular axis, but also induces a directed torque along this axis, which results in a transient orientation of the molecules. The asymmetric molecules are chiral in nature and different molecular enantiomers experience the orienting action in opposite directions causing out-of-phase oscillations of their dipole moments. The resulting microwave radiation was recently suggested to be used for analysis or discrimination of chiral molecular mixtures. We reveal the mechanism behind this laser-induced orientation effect, show that it is classical in nature, and envision further applications of light with twisted polarization.

  • Questioning the Recent Observation of Quantum Hawking Radiation

    Leonhardt U. (2018) Annalen der Physik.
    A recent article [J. Steinhauer, Nat. Phys. 2016, 12, 959] has reported the observation of quantum Hawking radiation and its entanglement in an analogue black hole. Here, the published evidence, its consistency with theoretical bounds, and the statistical significance of the results are analyzed. The analysis raises severe doubts on the observation of Hawking radiation.

  • Impulsive Raman spectroscopy via precision measurement of frequency shift with low energy excitation

    Raanan D., Ren L., Oron D. & Silberberg Y. (2018) Optics Letters.
    Stimulated Raman scattering (SRS) has recently become useful for chemically selective bioimaging. It is usually measured via modulation transfer from the pump beam to the Stokes beam. Impulsive stimulated Raman spectroscopy, on the other hand, relies on the spectral shift of ultrashort pulses as they propagate in a Raman active sample. This method was considered impractical with low energy pulses since the observed shifts are very small compared to the excitation pulse bandwidth, spanning many terahertz. Here we present a new apparatus, using tools borrowed from the field of precision measurement, for the detection of low-frequency Raman lines via stimulated-Raman-scattering-induced spectral shifts. This method does not require any spectral filtration and is therefore an excellent candidate to resolve low-lying Raman lines (

  • A Mechanistic Study of Phase Transformation in Perovskite Nanocrystals Driven by Ligand Passivation

    Udayabhaskararao T., Houben L., Cohen H., Menahem M., Pinkas I., Avram L., Wolf T., Teitelboim A., Leskes M., Yaffe O., Oron D. & Kazes M. (2018) Chemistry of Materials.
    Active control over the shape, composition, and crystalline habit of nanocrystals has long been a goal. Various methods have been shown to enable postsynthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement, and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can be induced at room temperature solely by modification of the ligand shell composition in solution. The reversible transformation of cubic CsPbX3 nanocrystals to rhombohedral Cs4PbX6 nanocrystals is achieved by controlling the ratio of oleylamine to oleic acid capping molecules. High-resolution transmission electron microscopy investigation of Cs4PbX6 reveals the growth habit of the rhombohedral crystal structure is composed of a zero-dimensional layered network of isolated PbX6 octahedra separated by Cs cation planes. The reversible transformation between the two phases involves an exfoliation and recrystalliztion process. This scheme enables fabrication of high-purity monodispersed Cs4PbX6 nanoparticles with controlled sizes. Also, depending on the final size of the Cs4PbX6 nanoparticles as tuned by the reaction time, the back reaction yields CsPbX3 nanoplatelets with a controlled thickness. In addition, detailed surface analysis provides insight into the impact of the ligand composition on surface stabilization that, consecutively, acts as the driving force in phase and shape transformations in cesium lead halide perovskites.

  • Temperature Rise under Two-Photon Optogenetic Brain Stimulation

    Picot A., Dominguez S., Liu C., Chen I., Tanese D., Ronzitti E., Berto P., Papagiakoumou E., Oron D., Tessier G., Forget B. C. & Emiliani V. (2018) Cell Reports.
    In recent decades, optogenetics has been transforming neuroscience research, enabling neuroscientists to drive and read neural circuits. The recent development in illumination approaches combined with two-photon (2P) excitation, either sequential or parallel, has opened the route for brain circuit manipulation with single-cell resolution and millisecond temporal precision. Yet, the high excitation power required for multi-target photostimulation, especially under 2P illumination, raises questions about the induced local heating inside samples. Here, we present and experimentally validate a theoretical model that makes it possible to simulate 3D light propagation and heat diffusion in optically scattering samples at high spatial and temporal resolution under the illumination configurations most commonly used to perform 2P optogenetics: single-and multi-spot holographic illumination and spiral laser scanning. By investigating the effects of photostimulation repetition rate, spot spacing, and illumination dependence of heat diffusion, we found conditions that make it possible to design a multi-target 2P optogenetics experiment with minimal sample heating.

  • Spatiotemporal supermodes: Rapid reduction of spatial coherence in highly multimode lasers

    Chriki R., Mahler S., Tradonsky C., Pal V., Friesem A. A. & Davidson N. (2018) Physical Review A.
    Spatial coherence quantifies spatial field correlations and is one of the fundamental properties of light. Here we investigate the spatial coherence of highly multimode lasers in the regime of short timescales. Counterintuitively, we show that in this regime, the temporal (longitudinal) modes play a crucial role in spatial coherence reduction. To evaluate the spatial coherence we measured the temporal dynamics of speckle fields generated by a highly multimode laser with over 10(5) lasing spatial (transverse) modes and examined the dependence of speckle contrast on the exposure time of the detecting device. We show that in the regime of short timescales, the spatial and temporal modes interact to form spatiotemporal supermodes, such that the spatial degrees of freedom are encoded onto the temporal modes. As a result, the speckle contrast is suppressed according to the number of temporal modes, and the degree of spatial coherence is reduced. Moreover, the functional form of the spatial coherence is shown to have a bimodal distribution. In the regime of long timescales, the supermodes are no longer a valid representation of the laser modal structure. Consequently, the spatial coherence is independent of the temporal modes, and the classical result, where the speckle contrast is suppressed according to the number of spatial modes, is obtained. Due to this spatiotemporal mechanism, highly multimode lasers can be used for speckle suppression in high-speed full-field imaging applications, as we demonstrate here for imaging of a fast moving object.

  • Probing New Long-Range Interactions by Isotope Shift Spectroscopy

    Berengut J. C., Budker D., Delaunay C., Flambaum V. V., Frugiuele C., Fuchs E., Grojean C., Harnik R., Ozeri R., Perez G. & Soreq Y. (2018) Physical Review Letters.
    We explore a method to probe new long- and intermediate-range interactions using precision atomic isotope shift spectroscopy. We develop a formalism to interpret linear King plots as bounds on new physics with minimal theory inputs. We focus only on bounding the new physics contributions that can be calculated independently of the standard model nuclear effects. We apply our method to existing Ca+ data and project its sensitivity to conjectured new bosons with spin-independent couplings to the electron and the neutron using narrow transitions in other atoms and ions, specifically, Sr and Yb. Future measurements are expected to improve the relative precision by 5 orders of magnitude, and they can potentially lead to an unprecedented sensitivity for bosons within the 0.3 to 10 MeV mass range.

  • Fault-tolerant detection of a quantum error

    Rosenblum S., Reinhold P., Mirrahimi M., Jiang L., Frunzio L. & Schoelkopf R. J. (2018) Science.
    A critical component of any quantum error-correcting scheme is detection of errors by using an ancilla system. However, errors occurring in the ancilla can propagate onto the logical qubit, irreversibly corrupting the encoded information. We demonstrate a fault-tolerant error-detection scheme that suppresses spreading of ancilla errors by a factor of 5, while maintaining the assignment fidelity. The same method is used to prevent propagation of ancilla excitations, increasing the logical qubit dephasing time by an order of magnitude. Our approach is hardware-efficient, as it uses a single multilevel transmon ancilla and a cavity-encoded logical qubit, whose interaction is engineered in situ by using an off-resonant sideband drive. The results demonstrate that hardware-efficient approaches that exploit system-specific error models can yield advances toward fault-tolerant quantum computation.

  • Vibrational spectroscopy via stimulated Raman induced Kerr lensing

    Raanan D., Luttig J., Silberberg Y. & Oron D. (2018) APL Photonics.
    We present a new method for the measurement of the stimulated Raman spectrum based on time-dependent spatial modulation of a laser beam as it passes through a Raman active medium. This effect is similar to the instantaneous Kerr lensing and Kerr deflection yet involves resonant vibrations which result in a time-dependent refractive index change. We use sub-nanojoule pulses together with a sensitive pump-probe measurement apparatus to excite and detect the fine (10(-5)-10(-4)) temporal and spatial variations in intensity resulting from the Raman-induced Kerr effect. We demonstrate the effect by changing the spatial overlap between the pump and probe at the sample and measuring the time-dependent deformation of the probe beam's cross section. This method is particularly useful for detection of low-frequency Raman lines, as we demonstrate by measuring the Raman spectrum of neat liquids in a cuvette.

  • Markovian heat sources with the smallest heat capacity

    Uzdin R., Gasparinetti S., Ozeri R. & Kosloff R. (2018) New Journal of Physics.
    Thermal Markovian dynamics is typically obtained by coupling a system to a sufficiently hot bath with a large heat capacity. Here we present a scheme for inducing Markovian dynamics using an arbitrarily small and cold heat bath. The scheme is based on injecting phase noise to the small bath. Markovianity emerges when the dephasing rate is larger than the system-bath coupling. Several unique signatures of small baths are studied. We discuss realizations in ion traps and superconducting qubits and show that it is possible to create an ideal setting where the system dynamics is indifferent to the internal bath dynamics.

  • The Organic Crystalline Materials of Vision: Structure-Function Considerations from the Nanometer to the Millimeter Scale

    Palmer B. A., Gur D., Weiner S., Addadi L. & Oron D. (2018) Advanced Materials.
    Vision mechanisms in animals, especially those living in water, are diverse. Many eyes have reflective elements that consist of multilayers of nanometer-sized crystalline plates, composed of organic molecules. The crystal multilayer assemblies owe their enhanced reflectivity to the high refractive indices of the crystals in preferred crystallographic directions. The high refractive indices are due to the molecular arrangements in their crystal structures. Herein, data regarding these difficult-to-characterize crystals are reviewed. This is followed by a discussion on the function of these crystalline assemblies, especially in visual systems whose anatomy has been well characterized under close to in vivo conditions. Three test cases are presented, and then the relations between the reflecting crystalline components and their functions, including the relations between molecular structure, crystal structure, and reflecting properties are discussed. Some of the underlying mechanisms are also discussed, and finally open questions in the field are identified.

  • Mineral Deposits in Ficus Leaves: Morphologies and Locations in Relation to Function

    Pierantoni M., Tenne R., Rephael B., Brumfeld V., van Casteren A., Kupczik K., Oron D., Addadi L. & Weiner S. (2018) Plant Physiology.
    Ficus trees are adapted to diverse environments and have some of the highest rates of photosynthesis among trees. Ficus leaves can deposit one or more of the three major mineral types found in leaves: amorphous calcium carbonate cystoliths, calcium oxalates, and silica phytoliths. In order to better understand the functions of these minerals and the control that the leaf exerts over mineral deposition, we investigated leaves from 10 Ficus species from vastly different environments (Rehovot, Israel; Bologna, Italy; Issa Valley, Tanzania; and Ngogo, Uganda). We identified the mineral locations in the soft tissues, the relative distributions of the minerals, and mineral volume contents using microcomputed tomography. Each Ficus species is characterized by a unique 3D mineral distribution that is preserved in different environments. The mineral distribution patterns are generally different on the adaxial and abaxial sides of the leaf. All species examined have abundant calcium oxalate deposits around the veins. We used micromodulated fluorimetry to examine the effect of cystoliths on photosynthetic efficiency in two species having cystoliths abaxially and adaxially (Ficus microcarpa) or only abaxially (Ficus carica). In F. microcarpa, both adaxial and abaxial cystoliths efficiently contributed to light redistribution inside the leaf and, hence, increased photosynthetic efficiency, whereas in F. carica, the abaxial cystoliths did not increase photosynthetic efficiency.

  • Selective Orientation of Chiral Molecules by Laser Fields with Twisted Polarization

    Tutunnikov I., Gershnabel E., Gold S. & Averbukh I. S. (2018) Journal of Physical Chemistry Letters.
    We explore a pure optical method for enantioselective orientation of chiral molecules by means of laser fields with twisted polarization. Several field implementations are considered, including a pair of delayed, cross-polarized laser pulses, an optical centrifuge, and polarization-shaped pulses. We show that these schemes lead to out-of-phase time-dependent dipole signals for different enantiomers, and we also predict a substantial permanent molecular orientation persisting long after the laser fields are over. The underlying classical orientation mechanism common to all of these fields is discussed, and its operation is demonstrated for a range of chiral molecules of various complexity: hydrogen thioperoxide (HSOH), propylene oxide (CH3CHCH2O), and ethyl oxirane (CH3CH2CHCH2O). The presented results demonstrate generality, versatility, and robustness of this optical method for manipulating molecular enantiomers in the gas phase.

  • Phase‐Space Versus Coordinate‐Space Methods: Prognosis for Large Quantum Calculations

    Tannor D., Machnes S., Assemat E. & Larsson H. R. (2018) .
    This chapter provides a simple pedagogical presentation of the discrete variable representation (DVR). It reviews the von Neumann (vN) basis of phase‐space Gaussians which include the Projected von Neumann Basis (PvN) and the Biorthogonal von Neumann Basis (PvB). The chapter includes a variety of interesting formal properties of nonorthogonal bases that are an extension of the DVR presentation and provides insight into the method. It presents an analysis of multidimensional considerations, including details of a highly efficient tensor formulation for performing pruned multidimensional DVR calculations for sparse but unstructured grids. The chapter contains illustrative applications. Pruned phase‐space methods have been successfully used for computing eigenenergies of (ro‐) vibrational systems. The chapter focuses on the applications in the context of solving the time‐dependent Schrodinger equation (TDSE). The efficiency of phase‐space versus coordinate‐space methods will certainly depend on the particular system studied and the strength of coupling between degrees of freedom.

  • Optimizing the nonlinear optical response of plasmonic metasurfaces

    Blechman Y., Almeida E., Sain B. & Prior Y. (2018) .
    We demonstrate that the enhancement of nonlinear optical processes in plasmonic nanomaterials cannot be fully predicted by their linear properties.

  • Communication: Systematic elimination of Stokes divergences emanating from complex phase space caustics

    Koch W. & Tannor D. J. (2018) Journal of Chemical Physics.
    Stokes phenomenon refers to the fact that an asymptotic expansion of complex functions can differ in different regions of the complex plane, and that beyond the so-called Stokes lines the expansion has an unphysical divergence. An important special case is when the Stokes lines emanate from phase space caustics of a complex trajectory manifold. In this case, symmetry determines that to second order there is a double coverage of the space, one portion of which is unphysical. Building on the seminal but laconic findings of Adachi, we show that the deviation from second order can be used to rigorously determine the Stokes lines and therefore the region of the space that should be removed. The method has applications to wavepacket reconstruction from complex valued classical trajectories. With a rigorous method in hand for removing unphysical divergences, we demonstrate excellent wavepacket reconstruction for the Morse, Quartic, Coulomb, and Eckart systems.

  • Electronic zero-point fluctuation forces inside circuit components

    Shahmoon E. & Leonhardt U. (2018) Science Advances.
    One of the most intriguing manifestations of quantum zero-point fluctuations are the van der Waals and Casimir forces, often associated with vacuum fluctuations of the electromagnetic field. We study generalized fluctuation potentials acting on internal degrees of freedom of components in electrical circuits. These electronic Casimir-like potentials are induced by the zero-point current fluctuations of any general conductive circuit. For realistic examples of an electromechanical capacitor and a superconducting qubit, our results reveal the possibility of tunable forces between the capacitor plates, or the level shifts of the qubit, respectively. Our analysis suggests an alternative route toward the exploration of Casimir-like fluctuation potentials, namely, by characterizing and measuring them as a function of parameters of the environment. These tunable potentials may be useful for future nanoelectromechanical and quantum technologies.

  • Classical analog of the Unruh effect

    Leonhardt U., Griniasty I., Wildeman S., Fort E. & Fink M. (2018) Physical Review A.
    In the Unruh effect an observer with constant acceleration perceives the quantum vacuum as thermal radiation. The Unruh effect has been believed to be a pure quantum phenomenon, but here we show theoretically how the effect arises from the correlation of noise, regardless of whether this noise is quantum or classical. We demonstrate this idea with a simple experiment on water waves where we see the first indications of a Planck spectrum in the correlation energy.

  • Spectrally narrow features in a supercontinuum generated by shaped pulse trains

    Yallapragada V. J., Rigneault H. & Oron D. (2018) Optics Express.
    Supercontinuum generation using photonic crystal fibers is a useful technique to generate light spanning a broad wavelength range, using femtosecond laser pulses. For some applications, one may desire higher power density at specific wavelengths. Increasing the pump power results primarily in further broadening of the output spectrum and is not particularly useful for this purpose. In this paper we demonstrate that by applying a periodic spectral phase modulation to the input pulse using a pulse shaper, the spectral energy density of the output supercontinuum can be enhanced by nearly an order of magnitude at specific wavelengths, which are tunable. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

  • High phase space density loading of a falling magnetic trap

    Almog I., Coslovsky J., Loewenthal G., Courvoisier A. & Davidson N. (2018) Applied Physics B: Lasers and Optics.
    Loading an ultra-cold ensemble into a static magnetic trap involves unavoidable loss of phase space density when the gravitational energy dominates the kinetic energy of the ensemble. In such a case the gravitational energy is transformed into heat, making a subsequent evaporation process slower and less efficient. We apply a high phase space loading scheme on a sub-doppler cooled ensemble of Rubidium atoms, with a gravitational energy much higher than its temperature of . Using the regular configuration of a quadrupole magnetic trap, but driving unequal currents through the coils to allow the trap center to fall, we dissipate most of the gravitational energy and obtain a 20-fold improvement in the phase space density as compared to optimal loading into a static magnetic trap. Applying this scheme, we start an efficient and fast evaporation process as a result of the sub-second thermalization rate of the magnetically trapped ensemble.

  • Programmable Interference between Two Microwave Quantum Memories

    Gao Y. Y., Lester B. J., Zhang Y., Wang C., Rosenblum S., Frunzio L., Jiang L., Girvin S. M. & Schoelkopf R. J. (2018) Physical Review X.
    Interference experiments provide a simple yet powerful tool to unravel fundamental features of quantum physics. Here we engineer a driven, time-dependent bilinear coupling that can be tuned to implement a robust 50:50 beam splitter between stationary states stored in two superconducting cavities in a three-dimensional architecture. With this, we realize high-contrast Hong-Ou-Mandel interference between two spectrally detuned stationary modes. We demonstrate that this coupling provides an efficient method for measuring the quantum state overlap between arbitrary states of the two cavities. Finally, we showcase concatenated beam splitters and differential phase shifters to implement cascaded Mach-Zehnder interferometers, which can control the signature of the two-photon interference on demand. Our results pave the way toward implementation of scalable boson sampling, the application of linear optical quantum computing protocols in the microwave domain, and quantum algorithms between long-lived bosonic memories.

  • Numerical study of laser energy effects on density transition injection in laser wakefield acceleration

    Massimo F., Lifschitz A. F., Thaury C. & Malka V. (2018) Plasma Physics and Controlled Fusion.
    Density transition (or shock-front) injection is a technique to obtain high quality electron beams in laser wakefield acceleration. This technique, which requires no additional laser pulse, is easy to implement and is receiving increasing interest. In addition to its performances, its setup realized with a blade inserted in a gas jet allows a certain flexibility in controlling the density transition shape, whose effects on the beam quality have been studied theoretically and experimentally. We report the results of particle-in-cell simulations where the laser energy is systematically varied for different shapes of the density transition. Our study shows how the laser energy affects the injection process, increasing the injected charge and influencing the other beam characteristics (e.g. energy and duration).

  • Phase Locking between Different Partial Waves in Atom-Ion Spin-Exchange Collisions

    Sikorsky T., Morita M., Meir Z., Buchachenko A. A., Ben-Shlomi R., Akerman N., Narevicius E., Tscherbul T. V. & Ozeri R. (2018) Physical review letters.
    We present a joint experimental and theoretical study of spin dynamics of a single Sr-88(+) ion colliding with an ultracold cloud of Rb atoms in various hyperfine states. While spin exchange between the two species occurs after 9.1(6) Langevin collisions on average, spin relaxation of the Sr+ ion Zeeman qubit occurs after 48(7) Langevin collisions, which is significantly slower than in previously studied systems due to a small second-order spin-orbit coupling. Furthermore, a reduction of the endothermic spin-exchange rate is observed as the magnetic field is increased. Interestingly, we find that while the phases acquired when colliding on the spin singlet and triplet potentials vary largely between different partial waves, the singlet-triplet phase difference, which determines the spin-exchange cross section, remains locked to a single value over a wide range of partial waves, which leads to quantum interference effects.

  • Energy-Chirp Compensation in a Laser Wakefield Accelerator

    Dopp A., Thaury C., Guillaume E., Massimo F., Lifschitz A., Andriyash I., Goddet J. -., Tazfi A., Phuoc K. T. & Malka V. (2018) Physical Review Letters.
    The energy spread in laser wakefield accelerators is primarily limited by the energy chirp introduced during the injection and acceleration processes. Here, we propose the use of longitudinal density tailoring to reduce the beam chirp at the end of the accelerator. Experimental data sustained by quasi-3D particle-in-cell simulations show that broadband electron beams can be converted to quasimonoenergetic beams of ≤10% energy spread while maintaining a high charge of more than 120 pC. In the linear and quasilinear regimes of wakefield acceleration, the method could provide even lower, subpercent level, energy spread.

  • Chiral 2D Colloidal Semiconductor Quantum Wells

    Yang G., Kazes M. & Oron D. (2018) Advanced Functional Materials.
    Induced chirality in colloidal semiconductor nanoparticles has raised significant attention in the past few years as an extremely sensitive spectroscopic tool and due to the promising applications of chiral quantum dots in sensing, quantum optics, and spintronics. Yet, the origin of the induced chiroptical effects in semiconductor nanoparticles is still not fully understood, partly because almost all the theoretical and experimental studies to date are based on the simple model system of a spherical nanocrystal. Here, the realization of induced chirality in atomically flat 2D colloidal quantum wells is shown. A strong circular dichroism (CD) response as well as an absorptive-like CD line shape is observed in chiral CdSe nanoplatelets (NPLs), significantly differing from that previously observed in spherical dots. Furthermore, this intense CD signal almost completely disappears after coating with a very thin CdS shell. In contrast, CdSe-CdS core-crown NPLs exhibit a spectral response which seems to originate independently from the core and the crown regions of the NPL. This work on the one hand further advances the understanding of the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, and on the other opens a pathway toward applications using chiroptical materials.

  • Reductions to IID in Device-independent Quantum Information Processing

    Arnon-Friedman R. (2018) arXiv.
    The field of device-independent (DI) quantum information processing concerns itself with devising and analysing protocols, such as quantum key distribution, without referring to the quality of the physical devices utilised to execute the protocols. Instead, the analysis is based on the observed correlations that arise during a repeated interaction with the devices and, in particular, their ability to violate the so called Bell inequalities. Since the analysis of DI protocols holds irrespectively of the underlying physical device, it implies that any device can be used to execute the protocols: If the apparatus is of poor quality, the users of the protocol will detect it and abort; otherwise, they will accomplish their goal. This strong statement comes at a price-- the analysis of DI protocols is, a priori, extremely challenging. The thesis presents an approach that can be taken to simplify the analysis of DI information processing protocols. The idea is the following: Instead of analysing the most general device leading to the observed correlations, one should first analyse a significantly simpler device that, in each interaction with the user, behaves in an identical way, independently of all other interactions. We call such a device an independently and identically distributed (IID) device. As the next step, special techniques are used to prove that, without loss of generality, the analysis of the IID device implies similar results for the most general device. These are termed reductions to IID. We present two mathematical techniques that can be used as reductions to IID in the DI setting, each accompanied by a showcase-application that exemplifies the reduction's usage and benefits. Performing the analysis via a reduction to IID leads to simpler proofs and significant quantitive improvements, matching the tight results proven when analysing IID devices.

  • Light storage for one second in room-temperature alkali vapor

    Katz O. & Firstenberg O. (2018) Nature Communications.
    Light storage, the controlled and reversible mapping of photons onto long-lived states of matter, enables memory capability in optical quantum networks. Prominent storage media are warm alkali vapors due to their strong optical coupling and long-lived spin states. In a dense gas, the random atomic collisions dominate the lifetime of the spin coherence, limiting the storage time to a few milliseconds. Here we present and experimentally demonstrate a storage scheme that is insensitive to spin-exchange collisions, thus enabling long storage times at high atomic densities. This unique property is achieved by mapping the light field onto spin orientation within a decoherence-free subspace of spin states. We report on a record storage time of 1 s in room-temperature cesium vapor, a 100-fold improvement over existing storage schemes. Furthermore, our scheme lays the foundations for hour-long quantum memories using rare-gas nuclear spins.

  • High phase space density loading of a falling magnetic trap (vol 124, 158, 2018)

    Almog I., Coslovsky J., Loewenthal G., Courvoisier A. & Davidson N. (2018) Applied Physics B: Lasers and Optics.
    In the original publication of the article, typesetters have incorrectly processed.

  • Gap-mode-assisted light-induced switching of sub-wavelength magnetic domains

    Scheunert G., McCarron R., Kullock R., Cohen S. R., Rechav K., Kaplan-Ashiri I., Bitton O., Hecht B. & Oron D. (2018) Journal of Applied Physics.
    Creating sub-micron hotspots for applications such as heat-assisted magnetic recording (HAMR) is a challenging task. The most common approach relies on a surface-plasmon resonator (SPR), whose design dictates the size of the hotspot to always be larger than its critical dimension. Here, we present an approach which circumvents known geometrical restrictions by resorting to electric field confinement via excitation of a gap-mode (GM) between a comparatively large Gold (Au) nano-sphere (radius of 100 nm) and the magnetic medium in a grazing-incidence configuration. Operating a lambda = 785 nm laser, sub-200 nm hot spots have been generated and successfully used for GM-assisted magnetic switching on commercial CoCrPt perpendicular magnetic recording media at laser powers and pulse durations comparable to SPR-based HAMR. Lumerical electric field modelling confirmed that operating in the near-infrared regime presents a suitable working point where most of the light's energy is deposited in the magnetic layer, rather than in the nano-particle. Further, modelling is used for predicting the limits of our method which, in theory, can yield sub-30 nm hotspots for Au nano-sphere radii of 25-50 nm for efficient heating of FePt recording media with a gap of 5 nm. Published by AIP Publishing.

  • Atomic combination clocks

    Akerman N. & Ozeri R. (2018) New Journal of Physics.
    Atomic clocks use atomic transitions as frequency references. The susceptibility of the atomic transition to external fields limits clock stability and introduces systematic frequency shifts. Here, we propose to realize an atomic clock that utilizes an entangled superposition of states of multiple atomic species, where the reference frequency is a sum of the individual transition frequencies. The superposition is selected such that the susceptibilities of the respective transitions, in individual species, partially cancel leading to improved stability and a reduction in the corresponding systematic shifts. We present and analyze two examples of such combinations. The first uses the optical quadrupole transitions in a Ca-40(+)-Yb-174(+) two-ion system. The second is a superposition of optical quadrupole transitions in one Sr-88(+) ion and three Hg-202(+) ions. These combinations have reduced susceptibility to external magnetic fields and blackbody radiation.

  • Quantum Nonlinear Optics in Atomically Thin Materials

    Wild D. S., Shahmoon E., Yelin S. F. & Lukin M. D. (2018) Physical Review Letters.
    We show that a nonlinear optical response associated with a resonant, atomically thin material can be dramatically enhanced by placing it in front of a partially reflecting mirror, rendering otherwise weakly nonlinear systems suitable for experiments and applications involving quantum nonlinear optics. Our approach exploits the nonlinear response of long-lived polariton resonances that arise at particular distances between the material and the mirror. The scheme is entirely based on free-space optics, eliminating the need for cavities or complex nanophotonic structures. We analyze a specific implementation based on exciton-polariton resonances in two-dimensional semiconductors and discuss the role of imperfections and loss.

  • Self-Healing Inside APbBr3 Halide Perovskite Crystals

    Ceratti D. R., Rakita Y., Cremonesi L., Tenne R., Kalchenko V., Elbaum M., Oron D., Potenza M. A. C., Hodes G. & Cahen D. (2018) Advanced Materials.
    Self-healing, where a modification in some parameter is reversed with time without any external intervention, is one of the particularly interesting properties of halide perovskites. While there are a number of studies showing such self-healing in perovskites, they all are carried out on thin films, where the interface between the perovskite and another phase (including the ambient) is often a dominating and interfering factor in the process. Here, self-healing in perovskite (methylammonium, formamidinium, and cesium lead bromide (MAPbBr3, FAPbBr3, and CsPbBr3)) single crystals is reported, using two-photon microscopy to create damage (photobleaching) ≈110 µm inside the crystals and to monitor the recovery of photoluminescence after the damage. Self-healing occurs in all three perovskites with FAPbBr3 the fastest (≈1 h) and CsPbBr3 the slowest (tens of hours) to recover. This behavior, different from surface-dominated stability trends, is typical of the bulk and is strongly dependent on the localization of degradation products not far from the site of the damage. The mechanism of self-healing is discussed with the possible participation of polybromide species. It provides a closed chemical cycle and does not necessarily involve defect or ion migration phenomena that are often proposed to explain reversible phenomena in halide perovskites.

  • Single-shot noninterferometric measurement of the phase transmission matrix in multicore fibers

    Sivankutty S., Tsvirkun V., Bouwmans G., Andresen E. R., Oron D., Rigneault H. & Alons M. A. (2018) Optics Letters.
    A simple technique for far-field single-shot noninterferometric determination of the phase transmission matrix of a multicore fiber with over 100 cores is presented. This phase retrieval technique relies on the aperiodic arrangement of the cores. (C) 2018 Optical Society of America

  • Two-level masers as heat-to-work converters

    Ghosh A., Gelbwaser-Klimovsky D., Niedenzu W., Lvovsky A., Mazets I., Scully M. O. & Kurizki G. (2018) Proceedings Of The National Academy Of Sciences Of The United States Of America-Physical Sciences.
    Heat engines, which cyclically transform heat into work, are ubiquitous in technology. Lasers and masers may be viewed as heat engines that rely on population inversion or coherence in the active medium. Here we put forward an unconventional paradigm of a remarkably simple and robust electromagnetic heat-powered engine that bears basic differences to any known maser or laser: The proposed device makes use of only one Raman transition and does not rely on population inversion or coherence in its two-level working medium. Nor does it require any coherent driving. The engine can be powered by the ambient temperature difference between the sky and the ground surface. Its autonomous character and "free" power source make this engine conceptually and technologically enticing.

  • Hybrid PbS Quantum-Dot-in-Perovskite for High-Efficiency Perovskite Solar Cell

    Han J., Luo S., Yin X., Zhou Y., Nan H., Li J., Li X., Oron D., Shen H. & Lin H. (2018) Small.
    In this study, a facile and effective approach to synthesize high-quality perovskite-quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH3NH3PbI3 (MAPbI(3)) precursor to form a QD-in-perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X-ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI(3)-PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over approximate to 0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.

  • New Methods for Testing Lorentz Invariance with Atomic Systems

    Shaniv R., Ozeri R., Safronova M. S., Porsev S. G., Dzuba V. A., Flambaum V. V. & Haffner H. (2018) Physical Review Letters.
    We describe a broadly applicable experimental proposal to search for the violation of local Lorentz invariance (LLI) with atomic systems. The new scheme uses dynamic decoupling and can be implemented in current atomic clock experiments, with both single ions and arrays of neutral atoms. Moreover, the scheme can be performed on systems with no optical transitions, and therefore it is also applicable to highly charged ions which exhibit a particularly high sensitivity to Lorentz invariance violation. We show the results of an experiment measuring the expected signal of this proposal using a two-ion crystal of Sr-88(+) ions. We also carry out a systematic study of the sensitivity of highly charged ions to LLI to identify the best candidates for the LLI tests.

  • Experimental apparatus for overlapping a ground-state cooled ion with ultracold atoms

    Meir Z., Sikorsky T., Ben-shlomi R., Akerman N., Pinkas M., Dallal Y. & Ozeri R. (2018) Journal of Modern Optics.
    Experimental realizations of charged ions and neutral atoms in overlapping traps are gaining increasing interest due to their wide research application ranging from chemistry at the quantum level to quantum simulations of solid state systems. In this paper, we describe our experimental system in which we overlap a single ground-state cooled ion trapped in a linear Paul trap with a cloud of ultracold atoms such that both constituents are in the µK regime. Excess micromotion (EMM) currently limits atom–ion interaction energy to the mK energy scale and above. We demonstrate spectroscopy methods and compensation techniques which characterize and reduce the ion’s parasitic EMM energy to the µK regime even for ion crystals of several ions. We further give a substantial review on the non-equilibrium dynamics which governs atom–ion systems. The non-equilibrium dynamics is manifested by a power law distribution of the ion’s energy. We also give an overview on the coherent and non-coherent thermometry tools which can be used to characterize the ion’s energy distribution after single to many atom–ion collisions.

  • Spin-controlled atom-ion chemistry

    Sikorsky T., Meir Z., Ben-shlomi R., Akerman N. & Ozeri R. (2018) Nature Communications.
    Quantum control of chemical reactions is an important goal in chemistry and physics. Ultracold chemical reactions are often controlled by preparing the reactants in specific quantum states. Here we demonstrate spin-controlled atom–ion inelastic (spin-exchange) processes and chemical (charge-exchange) reactions in an ultracold Rb-Sr+ mixture. The ion’s spin state is controlled by the atomic hyperfine spin state via spin-exchange collisions, which polarize the ion’s spin parallel to the atomic spin. We achieve ~ 90% spin polarization due to the absence of strong spin-relaxation channel. Charge-exchange collisions involving electron transfer are only allowed for (RbSr)+ colliding in the singlet manifold. Initializing the atoms in various spin states affects the overlap of the collision wave function with the singlet molecular manifold and therefore also the reaction rate. Our observations agree with theoretical predictions.

  • Quantum engine efficiency bound beyond the second law of thermodynamics

    Niedenzu W., Mukherjee V., Ghosh A., Kofman A. G. & Kurizki G. (2018) Nature Communications.
    According to the second law, the efficiency of cyclic heat engines is limited by the Carnot bound that is attained by engines that operate between two thermal baths under the reversibility condition whereby the total entropy does not increase. Quantum engines operating between a thermal and a squeezed-thermal bath have been shown to surpass this bound. Yet, their maximum efficiency cannot be determined by the reversibility condition, which may yield an unachievable efficiency bound above unity. Here we identify the fraction of the exchanged energy between a quantum system and a bath that necessarily causes an entropy change and derive an inequality for this change. This inequality reveals an efficiency bound for quantum engines energised by a non-thermal bath. This bound does not imply reversibility, unless the two baths are thermal. It cannot be solely deduced from the laws of thermodynamics.

  • Characterizing the Quantum-Confined Stark Effect in Semiconductor Quantum Dots and Nanorods for Single-Molecule Electrophysiology

    Kuo Y., Li J., Michalet X., Chizhik A., Meir N., Bar-Elli O., Chan E., Oron D., Enderlein J. & Weiss S. (2018) ACS Photonics.
    We optimized the performance of quantum-confined Stark effect (QCSE)-based voltage nanosensors. A high throughput approach for single-particle QCSE characterization was developed and utilized to screen a library of such nanosensors. Type-II ZnSe/CdS-seeded nanorods were found to have the best performance among the different nanosensors evaluated in this work. The degree of correlation between intensity changes and spectral changes of the exciton's emission under an applied field was characterized. An upper limit for the temporal response of individual ZnSe/CdS nanorods to voltage modulation was characterized by high-throughput, high temporal resolution intensity measurements using a novel photon counting camera. The measured 3.5 mu s response time is limited by the voltage modulation electronics and represents,similar to 30 times higher bandwidth than needed for recording an action potential in a neuron.

  • Attosecond time-resolved photoelectron holography

    Porat G., Alon G., Rozen S., Pedatzur O., Kruger M., Azoury D., Natan A., Orenstein G., Bruner B. D., Vrakking M. J. J. & Dudovich N. (2018) Nature Communications.
    Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography-all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds.

  • Fast, noise-free memory for photon synchronization at room temperature

    Finkelstein R., Poem E., Michel O., Lahad O. & Firstenberg O. (2018) Science advances.
    Future quantum photonic networks require coherent opticalmemories for synchronizing quantum sources and gates of probabilistic nature. We demonstrate a fast ladder memory (FLAME) mapping the optical field onto the superposition between electronic orbitals of rubidium vapor. Using a ladder-level system of orbital transitions with nearly degenerate frequencies simultaneously enables high bandwidth, low noise, and long memory lifetime. We store and retrieve 1.7-ns-long pulses, containing 0.5 photons on average, and observe short-time external efficiency of 25%, memory lifetime (1/e) of 86 ns, and below 10(-4) added noise photons. Consequently, coupling this memory to a probabilistic source would enhance the on-demand photon generation probability by a factor of 12, the highest number yet reported for a noise-free, room temperature memory. This paves the way toward the controlled production of large quantum states of light from probabilistic photon sources.

  • A CNOT gate between multiphoton qubits encoded in two cavities

    Rosenblum S., Gao Y. Y., Reinhold P., Wang C., Axline C. J., Frunzio L., Girvin S. M., Jiang L., Mirrahimi M., Devoret M. H. & Schoelkopf R. J. (2018) Nature Communications.
    Entangling gates between qubits are a crucial component for performing algorithms in quantum computers. However, any quantum algorithm must ultimately operate on error-protected logical qubits encoded in high-dimensional systems. Typically, logical qubits are encoded in multiple two-level systems, but entangling gates operating on such qubits are highly complex and have not yet been demonstrated. Here we realize a controlled NOT (CNOT) gate between two multiphoton qubits in two microwave cavities. In this approach, we encode a qubit in the high-dimensional space of a single cavity mode, rather than in multiple two-level systems. We couple two such encoded qubits together through a transmon, which is driven by an RF pump to apply the gate within 190 ns. This is two orders of magnitude shorter than the decoherence time of the transmon, enabling a high-fidelity gate operation. These results are an important step towards universal algorithms on error-corrected logical qubits.

  • Noise-tolerant testing of high entanglement of formation

    Arnon-Friedman R. & Yuen H. (2018) .
    In this work we construct tests that allow a classical user to certify high dimensional entanglement in uncharacterized and possibly noisy quantum devices. We present a family of non-local games (G<sub>n</sub>) that for all n certify states with entanglement of formation (n). These tests can be derived from any bipartite non-local game with a classical-quantum gap. Furthermore, our tests are noise-tolerant in the sense that fault tolerant technologies are not needed to play the games; entanglement distributed over noisy channels can pass with high probability, making our tests relevant for realistic experimental settings. This is in contrast to, e.g., results on self-testing of high dimensional entanglement, which are only relevant when the noise rate goes to zero with the system's size n. As a corollary of our result, we supply a lower-bound on the entanglement cost of any state achieving a quantum advantage in a bipartite non-local game. Our proof techniques heavily rely on ideas from the work on classical and quantum parallel repetition theorems.

  • Multivalued classical mechanics arising from singularity loops in complex time

    Koch W. & Tannor D. J. (2018) Journal of Chemical Physics.
    Complex-valued classical trajectories in complex time encounter singular times at which the momentum diverges. A closed time contour around such a singular time may result in final values for q and p that differ from their initial values. In this work, we develop a calculus for determining the exponent and prefactor of the asymptotic time dependence of p from the singularities of the potential as the singularity time is approached. We identify this exponent with the number of singularity loops giving distinct solutions to Hamilton's equations of motion. The theory is illustrated for the Eckart, Coulomb, Morse, and quartic potentials. Collectively, these potentials illustrate a wide variety of situations: poles and essential singularities at finite and infinite coordinate values. We demonstrate quantitative agreement between analytical and numerical exponents and prefactors, as well as the connection between the exponent and the time circuit count. This work provides the theoretical underpinnings for the choice of time contours described in the studies of Doll et al. [J. Chem. Phys. 58(4), 1343-1351 (1973)] and Petersen and Kay [J. Chem. Phys. 141(5), 054114 (2014)]. It also has implications for wavepacket reconstruction from complex classical trajectories when multiple branches of trajectories are involved.

  • Physical mechanism of the electron-ion coupled transverse instability in laser pressure ion acceleration for different regimes

    Wan Y., Pai C. -., Zhang C. J., Li F., Wu Y. P., Hua J. F., Lu W., Joshi C., Mori W. B. & Malka V. (2018) Physical Review E.
    In radiation pressure ion acceleration (RPA) research, the transverse stability within laser plasma interaction has been a long-standing, crucial problem over the past decades. In this paper, we present a one-dimensional two-fluid theory extended from a recent work Wan et al. Phys. Rev. Lett. 117, 234801 (2016)PRLTAO0031-900710.1103/PhysRevLett.117.234801 to clearly clarify the origin of the intrinsic transverse instability in the RPA process. It is demonstrated that the purely growing density fluctuations are more likely induced due to the strong coupling between the fast oscillating electrons and quasistatic ions via the ponderomotive force with spatial variations. The theory contains a full analysis of both electrostatic (ES) and electromagnetic modes and confirms that the ES mode actually dominates the whole RPA process at the early linear stage. By using this theory one can predict the mode structure and growth rate of the transverse instability in terms of a wide range of laser plasma parameters. Two-dimensional particle-in-cell simulations are systematically carried out to verify the theory and formulas in different regimes, and good agreements have been obtained, indicating that the electron-ion coupled instability is the major factor that contributes the transverse breakup of the target in RPA process.

  • Plasmonic flat surface Fabry-Perot interferometry

    Sain B., Kaner R., Bondy Y. & Prior Y. (2018) Nanophotonics.
    We report measurements of the optical transmission through a plasmonic flat surface interferometer. The transmission spectrum shows Fabry-Perot-like modes, where for each mode order, the maximal transmission occurs at a gap that grows linearly with wavelength, giving the appearance of diagonal dependence on gap and wavelength. The experimental results are supported by numerical solutions of the wave equations and by a simplified theoretical model that is based on the coupling between localized and propagating surface plasmon. This work explains not only the appearance of the modes but also their sharp dependence on the gap, taking into consideration the refractive indices of the surrounding media. The transmission spectra provide information about the phase difference between the light impinging on the two cavities, enabling interferometric measurement of the light phase by transmission through the coupled plasmonic cavities. The 1° phase-difference resolution is obtained without any propagation distance, thus making this interferometer suitable for on-chip operation.

  • The Dual Functional Reflecting Iris of the Zebrafish

    Gur D., Nicolas J., Brumfeld V., Bar-Elli O., Oron D. & Levkowitz G. (2018) Advanced Science.
    Many marine organisms have evolved a reflective iris to prevent unfocused light from reaching the retina. The fish iris has a dual function, both to camouflage the eye and serving as a light barrier. Yet, the physical mechanism that enables this dual functionality and the benefits of using a reflective iris have remained unclear. Using synchrotron microfocused diffraction, cryo-scanning electron microscopy imaging, and optical analyses on zebrafish at different stages of development, it is shown that the complex optical response of the iris is facilitated by the development of high-order organization of multilayered guanine-based crystal reflectors and pigments. It is further demonstrated how the efficient light reflector is established during development to allow the optical functionality of the eye, already at early developmental stages.

  • Synchronization of strongly interacting alkali-metal spins

    Katz O. & Firstenberg O. (2018) Physical Review A.
    The spins of gaseous alkali-metal atoms are commonly assumed to oscillate at a constant hyperfine frequency, which for many years has been used to define a standard unit of time, the second. Indeed, under standard experimental conditions, the spins oscillate independently, only weakly perturbed and slowly decaying due to random spin-spin collisions. Here we consider a different, unexplored regime of very dense gas, where collisions, more frequent than the hyperfine frequency, dominate the dynamics. We find that the hyperfine oscillations become significantly longer lived, and their frequency becomes dependent on the state of the ensemble, manifesting strong nonlinear dynamics. We reveal that the nonlinearity originates from a many-body interaction which synchronizes the electronic spins, driving them into a single collective mode. The conditions for experimental realizations of this regime are outlined.

  • Generating flat-top beams with extended depth of focus

    Pal V., Tradonsky C., Chriki R., Kaplan N., Brodsky A., Attia M., Davidson N. & Friesem A. A. (2018) Applied Optics.
    Two approaches for generating flat-top beams (uniform intensity profile) with extended depth of focus are presented. One involves two diffractive optical elements (DOEs) and the other only a single DOE. The results indicate that the depth of focus of such beams strongly depends on the phase distribution at the output of the DOEs. By having uniform phase distribution, it is possible to generate flat-top beams with extended depth of focus. (C) 2018 Optical Society of America

  • A passive photon–atom qubit swap operation

    Bechler O., Borne A., Rosenblum S., Guendelman G., Mor O. E., Netser M., Ohana T., Aqua Z., Drucker N., Finkelstein R., Lovsky Y., Bruch R., Gurovich D., Shafir E. & Dayan B. (2018) Nature Physics.
    Deterministic quantum interactions between single photons and single quantum emitters are a vital building block towards the distribution of quantum information between remote systems(1-4). Deterministic photon-atom state transfer has previously been demonstrated with protocols that include active feedback or synchronized control pulses(5-10). Here we demonstrate a passive swap operation between the states of a single photon and a single atom. The underlying mechanism is single-photon Raman interaction(11-15)-an interference-based scheme that leads to deterministic interaction between two photonic modes and the two ground states of a Lambda-system. Using a nanofibre-coupled microsphere resonator coupled to single Rb atoms, we swap a photonic qubit into the atom and back, demonstrating fidelities exceeding the classical threshold of 2/3 in both directions. In this simultaneous write and read process, the returning photon, which carries the readout of the atomic qubit, also heralds the successful arrival of the write photon. Requiring no control fields, this single-step gate takes place automatically at the timescale of the atom's cavity-enhanced spontaneous emission. Applicable to any waveguide-coupled Lambda-system, this mechanism, which can also be harnessed to construct universal gates(16,17), provides a versatile building block for the modular scaling up of quantum information systems.

  • Quantum Lamarckism: observation, control and decoherence

    Kurizki G. & Kofman A. G. (2018) Physica Scripta.
    The purpose of this article, which is our contribution to Wolfgang Schleich's Festschrift, is to present an unconventional perspective of two fundamental, interrelated problems: the emergence of classicality and the observer's role in quantum mechanics. In our perspective, the decoherence of quantum states of a system or its measuring device (meter) by the environment cannot replace the role of the observer, nor can it provide the ultimate explanation of the transition of the system from quantumness to classicality. The reason is that decoherence, despite appearances, typically does not irretrievably obliterate the information on the system's state. Even in cases where the environment has the potential of erasing this information, the observer can negate decoherence effects in the meter or the system by dynamical control. We contend that the choice of measuring bases and observables is largely up to the controller-observer (CO) that need not possess unlimited resources in order to steer or freeze (at will) the system-state evolution and its quantumness, notwithstanding the environment effects. An analogy is drawn between the outlined approach and Lamarckism, the theory of evolution that preceded Darwinism. Quantum Lamarckism expresses our view of evolution as functional adaptation of the system to the interplay between environmental and CO effects. In our view, both conceptually and practically, decoherence may be deemed non-essential for determining the evolution of a quantum system embedded in its environment, provided the CO has an adequate, albeit limited, arsenal of resources.

  • Strong light-matter interaction in tungsten disulfide nanotubes

    Yadgarov L., Visic B., Abir T., Tenne R., Polyakov A. Y., Levi R., Dolgova T. V., Zubyuk V. V., Fedyanin A. A., Goodilin E. A., Ellenbogen T., Tenne R. & Oron D. (2018) Physical Chemistry Chemical Physics.
    Transition metal dichalcogenide materials have recently been shown to exhibit a variety of intriguing optical and electronic phenomena. Focusing on the optical properties of semiconducting WS2 nanotubes, we show here that these nanostructures exhibit strong light-matter interaction and form exciton-polaritons. Namely, these nanotubes act as quasi 1-D polaritonic nano-systems and sustain both excitonic features and cavity modes in the visible-near infrared range. This ability to confine light to subwavelength dimensions under ambient conditions is induced by the high refractive index of tungsten disulfide. Using "finite-difference time-domain'' (FDTD) simulations we investigate the interactions between the excitons and the cavity mode and their effect on the extinction spectrum of these nanostructures. The results of FDTD simulations agree well with the experimental findings as well as with a phenomenological coupled oscillator model which suggests a high Rabi splitting of similar to 280 meV. These findings open up possibilities for developing new concepts in nanotube-based photonic devices.

  • All-optical field-free three-dimensional orientation of asymmetric-top molecules

    Lin K., Tutunnikov I., Qiang J., Ma J., Song Q., Ji Q., Zhang W., Li H., Sun F., Gong X., Li H., Lu P., Zeng H., Prior Y., Averbukh I. S. & Wu J. (2018) Nature Communications.
    Orientation and alignment of molecules by ultrashort laser pulses is crucial for a variety of applications and has long been of interest in physics and chemistry, with the special emphasis on stereodynamics in chemical reactions and molecular orbitals imaging. As compared to the laser-induced molecular alignment, which has been extensively studied and demonstrated, achieving molecular orientation is a much more challenging task, especially in the case of asymmetric-top molecules. Here, we report the experimental demonstration of all-optical field-free three-dimensional orientation of asymmetric-top molecules by means of phase-locked cross-polarized two-color laser pulse. This approach is based on nonlinear optical mixing process caused by the off-diagonal elements of the molecular hyperpolarizability tensor. It is demonstrated on SO2 molecules and is applicable to a variety of complex nonlinear molecules.

  • Tunable, Flexible, and Efficient Optimization of Control Pulses for Practical Qubits

    Machnes S., Assemat E., Tannor D. & Wilhelm F. K. (2018) Physical Review Letters.
    Quantum computation places very stringent demands on gate fidelities, and experimental implementations require both the controls and the resultant dynamics to conform to hardware-specific constraints. Superconducting qubits present the additional requirement that pulses must have simple parameterizations, so they can be further calibrated in the experiment, to compensate for uncertainties in system parameters. Other quantum technologies, such as sensing, require extremely high fidelities. We present a novel, conceptually simple and easy-to-implement gradient-based optimal control technique named gradient optimization of analytic controls (GOAT), which satisfies all the above requirements, unlike previous approaches. To demonstrate GOAT's capabilities, with emphasis on flexibility and ease of subsequent calibration, we optimize fast coherence-limited pulses for two leading superconducting qubits architectures-flux-tunable transmons and fixed-frequency transmons with tunable couplers.

  • Direct Observation of Atom-Ion Nonequilibrium Sympathetic Cooling

    Meir Z., Pinkas M., Sikorsky T., Ben-shlomi R., Akerman N. & Ozeri R. (2018) Physical review letters.
    Sympathetic cooling is the process of energy exchange between a system and a colder bath. We investigate this fundamental process in an atom-ion experiment where the system is composed of a single ion trapped in a radio-frequency Paul trap and prepared in a classical oscillatory motion with total energy of similar to 200 K, and the bath is an ultracold cloud of atoms at mu K temperature. We directly observe the sympathetic cooling dynamics with single-shot energy measurements during one to several collisions in two distinct regimes. In one, collisions predominantly cool the system with very efficient momentum transfer leading to cooling in only a few collisions. In the other, collisions can both cool and heat the system due to nonequilibrium dynamics in the presence of the ion trap's oscillating electric fields. While the bulk of our observations agree well with a molecular-dynamics simulation of hard-sphere (Langevin) collisions, a measurement of the scattering angle distribution reveals forward-scattering (glancing) collisions which are beyond the Langevin model. This work paves the way for further nonequilibrium and collision dynamics studies using the well-controlled atom-ion system.

  • Practical device-independent quantum cryptography via entropy accumulation

    Arnon-Friedman R., Dupuis F., Fawzi O., Renner R. & Vidick T. (2018) Nature Communications.
    Device-independent cryptography goes beyond conventional quantum cryptography by providing security that holds independently of the quality of the underlying physical devices. Device-independent protocols are based on the quantum phenomena of non-locality and the violation of Bell inequalities. This high level of security could so far only be established under conditions which are not achievable experimentally. Here we present a property of entropy, termed "entropy accumulation", which asserts that the total amount of entropy of a large system is the sum of its parts. We use this property to prove the security of cryptographic protocols, including device-independent quantum key distribution, while achieving essentially optimal parameters. Recent experimental progress, which enabled loophole-free Bell tests, suggests that the achieved parameters are technologically accessible. Our work hence provides the theoretical groundwork for experimental demonstrations of device-independent cryptography.

  • Intra-cavity metasurfaces for topologically spin-controlled laser modes

    Maguid E., Chriki R., Yannai M., Tradonsky C., Kleiner V., Hasman E., Friesem A. A. & Davidson N. (2018) .
    We present the incorporation of a metasurface involving spin-orbit interaction phenomenon into a laser cavity paving the way for the generation of spin-controlled intra-cavity modes with different topologies.

  • Spectral and spatial shaping of a laser-produced ion beam for radiation-biology experiments

    Pommarel L., Vauzour B., Megnin-Chanet F., Bayart E., Delmas O., Goudjil F., Nauraye C., Letellier V., Pouzoulet F., Schillaci F., Romano F., Scuderi V., Cirrone G. A. P., Deutsch E., Flacco A. & Malka V. (2017) Physical Review Accelerators and Beams.
    The study of radiation biology on laser-based accelerators is most interesting due to the unique irradiation conditions they can produce, in terms of peak current and duration of the irradiation. In this paper we present the implementation of a beam transport system to transport and shape the proton beam generated by laser-target interaction for in vitro irradiation of biological samples. A set of four permanent magnet quadrupoles is used to transport and focus the beam, efficiently shaping the spectrum and providing a large and relatively uniform irradiation surface. Real time, absolutely calibrated, dosimetry is installed on the beam line, to enable shot-to-shot control of dose deposition in the irradiated volume. Preliminary results of cell sample irradiation are presented to validate the robustness of the full system.

  • Continuous generation of delayed light

    Smartsev S., Eger D., Davidson N. & Firstenberg O. (2017) Journal of Physics B: Atomic, Molecular and Optical Physics.
    We use a four-wave mixing process to read-out light from atomic coherence which is continuously written. The light is continuously generated after an effective delay, allowing the atomic coherence to evolve during the process. Contrary to slow-light delay, which depends on the medium optical depth, here the generation delay is determined solely by the intensive properties of the system, approaching the atomic coherence lifetime at the weak driving limit. The atomic evolution during the generation delay is further manifested in the spatial profile of the generated light due to atomic diffusion. Continuous generation of light with a long intrinsic delay can replace discrete write-read procedures when the atomic evolution is the subject of interest.

  • Revival of Raman coherence of trapped atoms

    Afek G., Coslovsky J., Mil A. & Davidson N. (2017) Physical Review A.
    We perform Raman spectroscopy of optically trapped noninteracting Rb87 atoms, and observe revivals of the atomic coherence at integer multiples of the trap period. The effect of coherence control methods such as echo and dynamical decoupling is investigated experimentally, analytically, and numerically, along with the effect of the anharmonicity of the trapping potential. The latter is shown to be responsible for incompleteness of the revivals. Coherent Raman control of trapped atoms can be useful in the context of free-oscillation atom interferometry and spatial multimode quantum memory.

  • Doppler cooling thermometry of a multilevel ion in the presence of micromotion

    Sikorsky T., Meir Z., Akerman N., Ben-Shlomi R. & Ozeri R. (2017) Physical Review A.
    We study the time-dependent fluorescence of an initially hot, multilevel, single atomic ion trapped in a radio-frequency Paul trap during Doppler cooling. We have developed an analytical model that describes the fluorescence dynamics during Doppler cooling which is used to extract the initial energy of the ion. While previous models of Doppler cooling thermometry were limited to atoms with a two-level energy structure and neglected the effect of the trap oscillating electric fields, our model applies to atoms with multilevel energy structure and takes into account the influence of micromotion on the cooling dynamics. This thermometry applies to any initial energy distribution. We experimentally test our model with an ion prepared in coherent, thermal, and Tsallis energy distributions.

  • AC Atom Interferometry with Quantum Lock-in Sensing

    Coslovsky J., Afek G. & Davidson N. (2017) .
    This paper describes a technique that allows measurement of very small alternating accelerations. It is based on a quantum version of a lock-in amplifier, 1 which filters out spectral components far from the frequency of the measured signal, improving the signal-to-noise ratio of the measurement. As a proof-of-principle, a controlled experiment using microwave radiation is performed, modulating the phase of the control pulses at a given frequency. A strong response at twice the modulation frequency is observed as expected. Preliminary results of measurements taken with Raman control are also presented, in which a controlled modulation of the phase was obtained by modulating a piezoelectric actuator, causing one of the Raman mirrors to vibrate.

  • Observation of Optomechanical Strain in a Cold Atomic Cloud

    Matzliah N., Edri H., Sinay A., Ozeri R. & Davidson N. (2017) Physical review letters.
    We report the observation of optomechanical strain applied to thermal and quantum degenerate Rb87 atomic clouds when illuminated by an intense, far detuned homogeneous laser beam. In this regime the atomic cloud acts as a lens that focuses the laser beam. As a backaction, the atoms experience a force opposite to the beam deflection, which depends on the atomic cloud density profile. We experimentally demonstrate the basic features of this force, distinguishing it from the well-established scattering and dipole forces. The observed strain saturates, ultimately limiting the momentum impulse that can be transferred to the atoms. This optomechanical force may effectively induce interparticle interactions, which can be optically tuned.

  • Observing Power-Law Dynamics of Position-Velocity Correlation in Anomalous Diffusion

    Afek G., Coslovsky J., Courvoisier A., Livneh O. & Davidson N. (2017) Physical Review Letters.
    In this Letter, we present a measurement of the phase-space density distribution (PSDD) of ultracold Rb-87 atoms performing 1D anomalous diffusion. The PSDD is imaged using a direct tomographic method based on Raman velocity selection. It reveals that the position-velocity correlation function C-xv(t) builds up on a time scale related to the initial conditions of the ensemble and then decays asymptotically as a power law. We show that the decay follows a simple scaling theory involving the power-law asymptotic dynamics of position and velocity. The generality of this scaling theory is confirmed using Monte Carlo simulations of two distinct models of anomalous diffusion.

  • A molecular quantum spin network controlled by a single qubit

    Schlipf L., Oeckinghaus T., Xu K., Dasari D. B. R., Zappe A., de Oliveira F. F., Kern B., Azarkh M., Drescher M., Ternes M., Kern K., Wrachtrup J. & Finkler A. (2017) Science Advances.
    Scalable quantum technologies require an unprecedented combination of precision and complexity for designing stable structures of well-controllable quantum systems on the nanoscale. It is a challenging task to find a suitable elementary building block, of which a quantum network can be comprised in a scalable way. We present the working principle of such a basic unit, engineered using molecular chemistry, whose collective control and readout are executed using a nitrogen vacancy (NV) center in diamond. The basic unit we investigate is a synthetic polyproline with electron spins localized on attached molecular side groups separated by a few nanometers. We demonstrate the collective readout and coherent manipulation of very few (

  • Casimir stress in materials: Hard divergency at soft walls

    Griniasty I. & Leonhardt U. (2017) Physical Review B.
    The Casimir force between macroscopic bodies is well understood, but not the Casimir stress inside bodies. Suppose empty space or a uniform medium meets a soft wall where the refractive index is continuous but its derivative jumps. For this situation we predict a characteristic power law for the stress inside the soft wall and close to its edges. Our result shows that such edges are not tolerated in the aggregation of liquids at surfaces, regardless whether the liquid is attracted or repelled.

  • Horizon 2020 EuPRAXIA design study

    Walker P. A., Alesini P. D., Alexandrova A. S., Anania M. P., Andreev N. E., Andriyash I., Aschikhin A., Assmann R. W., Audet T., Bacci A., Barna I. F., Beaton A., Beck A., Beluze A., Bernhard A., Bielawski S., Bisesto F. G., Boedewadt J., Brandi F., Bringer O., Brinkmann R., Bruendermann E., Buescher M., Bussmann M., Bussolino G. C., Chance A., Chanteloup J. C., Chen M., Chiadroni E., Cianchi A., Clarke J., Cole J., Couprie M. E., Croia M., Cros B., Dale J., Dattoli G., Delerue N., Delferriere O., Delinikolas P., Dias J., Dorda U., Ertel K., Pousa A. F., Ferrario M., Filippi F., Fils J., Fiorito R., Fonseca R. A., Galimberti M., Gallo A., Garzella D., Gastinel P., Giove D., Giribono A., Gizzi L. A., Gruener F. J., Habib A. F., Haefner L. C., Heinemann T., Hidding B., Holzer B. J., Hooker S. M., Hosokai T., Irman A., Jaroszynski D. A., Jaster-Merz S., Joshi C., Kaluza M. C., Kando M., Karger O. S., Karsch S., Khazanov E., Khikhlukha D., Knetsch A., Kocon D., Koester P., Kononenko O., Korn G., Kostyukov I., Labate L., Lechner C., Leemans W. P., Lehrach A., Li F. Y., Li X., Libov V., Lifschitz A., Litvinenko V., Lu W., Maier A. R., Malka V., Manahan G. G., Mangles S. P. D., Marchetti B., Marocchino A., De la Ossa A. M., Martins J. L., Massimo F., Mathieu F., Maynard G., Mehrling T. J., Molodozhentsev A. Y., Mosnier A., Mostacci A., Mueller A. S., Najmudin Z., Nghiem P. A. P., Nguyen F., Niknejadi P., Osterhoff J., Papadopoulos D., Patrizi B., Pattathil R., Petrillo V., Pocsai M. A., Poder K., Pompili R., Pribyl L., Pugacheva D., Romeo S., Rossi A. R., Roussel E., Sahai A. A., Scherkl P., Schramm U., Schroeder C. B., Schwindling J., Scifo J., Serafini L., Sheng Z. M., Silva L. O., Silva T., Simon C., Sinha U., Specka A., Streeter M. J. V., Svystun E. N., Symes D., Szwaj C., Tauscher G., Thomas A. G. R., Thompson N., Toci G., Tomassini P., Vaccarezza C., Vannini M., Vieira J. M., Villa F., Wahlstrom C., Walczak R., Weikum M. K., Welsch C. P., Wiemann C., Wolfenden J., Xia G., Yabashi M., Yu L., Zhu J. & Zigler A. (2017) Journal of Physics Conference Series.
    The Horizon 2020 Project EuPRAXIA ("European Plasma Research Accelerator with eXcellence In Applications") is preparing a conceptual design report of a highly compact and cost-effective European facility with multi-GeV electron beams using plasma as the acceleration medium. The accelerator facility will be based on a laser and/or a beam driven plasma acceleration approach and will be used for photon science, high-energy physics (HEP) detector tests, and other applications such as compact X-ray sources for medical imaging or material processing. EuPRAXIA started in November 2015 and will deliver the design report in October 2019. EuPRAXIA aims to be included on the ESFRI roadmap in 2020.

  • Induced Cavities for Photonic Quantum Gates

    Lahad O. & Firstenberg O. (2017) Physical review letters.
    Effective cavities can be optically induced in atomic media and employed to strengthen optical nonlinearities. Here we study the integration of induced cavities with a photonic quantum gate based on Rydberg blockade. Accounting for loss in the atomic medium, we calculate the corresponding finesse and gate infidelity. Our analysis shows that the conventional limits imposed by the blockade optical depth are mitigated by the induced cavity in long media, thus establishing the total optical depth of the medium as a complementary resource.

  • Tetragonal CH<sub>3</sub>NH<sub>3</sub>Pbi<sub>3</sub> is ferroelectric

    Rakita Y., Bar-Elli O., Meirzadeh E., Kaslasi H., Peleg Y., Hodes G., Lubomirsky I., Oron D., Ehre D. & Cahen D. (2017) Proceedings of the National Academy of Sciences of the United States of America.
    Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI<sub>3</sub>). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI<sub>3</sub> is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI<sub>3</sub> (unlike MAPbBr<sub>3</sub>) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material's relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity's hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI<sub>3</sub>, we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material's noncentrosymmetry. We note that thematerial's ferroelectric nature, can, but need not be important in a PV cell at room temperature.

  • Quantum lock-in force sensing using optical clock Doppler velocimetry

    Shaniv R. & Ozeri R. (2017) Nature Communications.
    Force sensors are at the heart of different technologies such as atomic force microscopy or inertial sensing. These sensors often rely on the measurement of the displacement amplitude of mechanical oscillators under applied force. The best sensitivity is typically achieved when the force is alternating at the mechanical resonance frequency of the oscillator, thus increasing its response by the mechanical quality factor. The measurement of low-frequency forces, that are below resonance, is a more difficult task as the resulting oscillation amplitudes are significantly lower. Here we use a single-trapped <sup>88</sup>Sr<sup>+</sup> ion as a force sensor. The ion is electrically driven at a frequency much lower than the trap resonance frequency. We measure small amplitude of motion by measuring the periodic Doppler shift of an atomic optical clock transition, enhanced using the quantum lock-in technique. We report frequency force detection sensitivity as low as 2.8 × 10<sup>-20</sup> NHz<sup>-1/2</sup>.

  • Calculation of Rydberg interaction potentials

    Weber S., Tresp C., Menke H., Urvoy A., Firstenberg O., Buechler H. P. & Hofferberth S. (2017) Journal of Physics B: Atomic, Molecular and Optical Physics.
    The strong interaction between individual Rydberg atoms provides a powerful tool exploited in an ever-growing range of applications in quantum information science, quantum simulation and ultracold chemistry. One hallmark of the Rydberg interaction is that both its strength and angular dependence can be fine-tuned with great flexibility by choosing appropriate Rydberg states and applying external electric and magnetic fields. More and more experiments are probing this interaction at short atomic distances or with such high precision that perturbative calculations as well as restrictions to the leading dipole-dipole interaction term are no longer sufficient. In this tutorial, we review all relevant aspects of the full calculation of Rydberg interaction potentials. We discuss the derivation of the interaction Hamiltonian from the electrostatic multipole expansion, numerical and analytical methods for calculating the required electric multipole moments and the inclusion of electromagnetic fields with arbitrary direction. We focus specifically on symmetry arguments and selection rules, which greatly reduce the size of the Hamiltonian matrix, enabling the direct diagonalization of the Hamiltonian up to higher multipole orders on a desktop computer. Finally, we present example calculations showing the relevance of the full interaction calculation to current experiments. Our software for calculating Rydberg potentials including all features discussed in this tutorial is available as open source.

  • Attosecond-resolved photoionization of chiral molecules

    Beaulieu S., Comby A., Clergerie A., Caillat J., Descamps D., Dudovich N., Fabre B., Geneaux R., Legare F., Petit S., Pons B., Porat G., Ruchon T., Taieb R., Blanchet V. & Mairesse Y. (2017) Science.
    Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light-propagation axis. We implemented self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wave packets emitted upon photoionization of camphor by circularly polarized laser pulses. We measured a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wave packets emitted through an autoionizing state further reveals the chiral character of strongly correlated electronic dynamics.

  • Plants and Light Manipulation: The Integrated Mineral System in Okra Leaves

    Pierantoni M., Tenne R., Brumfeld V., Kiss V., Oron D., Addadi L. & Weiner S. (2017) Advanced Science.
    Calcium oxalate and silica minerals are common components of a variety of plant leaves. These minerals are found at different locations within the leaf, and there is little conclusive evidence about the functions they perform. Here tools are used from the fields of biology, optics, and imaging to investigate the distributions of calcium oxalate, silica minerals, and chloroplasts in okra leaves, in relation to their functions. A correlative approach is developed to simultaneously visualize calcium oxalates, silica minerals, chloroplasts, and leaf soft tissue in 3D without affecting the minerals or the organic components. This method shows that in okra leaves silica and calcium oxalates, together with chloroplasts, form a complex system with a highly regulated relative distribution. This distribution points to a significant role of oxalate and silica minerals to synergistically optimize the light regime in the leaf. The authors also show directly that the light scattered by the calcium oxalate crystals is utilized for photosynthesis, and that the ultraviolet component of light passing through silica bodies, is absorbed. This study thus demonstrates that calcium oxalates increase the illumination level into the underlying tissue by scattering the incoming light, and silica reduces the amount of UV radiation entering the tissue.

  • Single-photon fiber bundle cameras (SFICAMs) for quantum enhanced superresolution microscopy

    Israel Y., Tenne R., Oron D. & Silberberg Y. (2017) .
    We present a method that utilizes quantum correlation measurements for multi-emitter sub-diffraction localization in a time-dependent scene. This is demonstrated using a newly developed imaging configuration based on fiber bundle coupled single-photon avalanche detectors.

  • Characterization of the ELIMED prototype permanent magnet quadrupole system

    Russo A. D., Schillaci F., Pommarel L., Romano F., Amato A., Amico A. G., Calanna A., Cirrone G. A. P., Costa M., Cuttone G., Amato C., De Luca G., Flacco F. A., Gallo G., Giove D., Grmek A., La Rosa G., Leanza R., Maggiore M., Malka V., Milluzzo G., Petringa G., Pipek J., Scuderi V., Vauzour B. & Zappala E. (2017) Journal of Instrumentation.
    The system described in this work is meant to be a prototype of a more performing one that will be installed at ELI-Beamlines in Prague for the collection of ions produced after the interaction Laser-target, [2]. It has been realized by the researchers of INFN-LNS (Laboratori Nazionali del Sud of the Instituto Nazionale di Fisica Nucleare) and SIGMAPHI, a French company, using a system of Permanent Magnet Quadrupoles (PMQs), [1]. The final system that will be installed in Prague is designed for protons and carbons up to 60MeV/u, around 10 times more than the energies involved in the present work. The prototype, shown in this work, has been tested in collaboration with the SAPHIR experimental facility group at LOA (Laboratoire d'Optique Applique) in Paris using a 200 TW Ti:Sapphire laser system. The purpose of this work is to validate the design and the performances of this large and compact bore system and to characterize the beam produced after the interaction laser-target and its features. Moreover, the optics simulations have been compared with a real beam shape on a GAF Chromic film. The procedure used during the experimental campaign and the most relevant results are reported here demonstrating a good agreement with the simulations and a good control on the beam optics.

  • Stable femtosecond X-rays with tunable polarization from a laser-driven accelerator

    Dopp A., Mahieu B., Lifschitz A., Thaury C., Doche A., Guillaume E., Grittani G., Lundh O., Hansson M., Gautier J., Kozlova M., Goddet J. P., Rousseau P., Tafzi A., Malka V., Rousse A., Corde S. & Phuoc K. T. (2017) Light: Science and Applications.
    Technology based on high-peak-power lasers has the potential to provide compact and intense radiation sources for a wide range of innovative applications. In particular, electrons that are accelerated in the wakefield of an intense laser pulse oscillate around the propagation axis and emit X-rays. This betatron source, which essentially reproduces the principle of a synchrotron at the millimeter scale, provides bright radiation with femtosecond duration and high spatial coherence. However, despite its unique features, the usability of the betatron source has been constrained by its poor control and stability. In this article, we demonstrate the reliable production of X-ray beams with tunable polarization. Using ionization-induced injection in a gas mixture, the orbits of the relativistic electrons emitting the radiation are reproducible and controlled. We observe that both the signal and beam profile fluctuations are significantly reduced and that the beam pointing varies by less than a tenth of the beam divergence. The polarization ratio reaches 80%, and the polarization axis can easily be rotated. We anticipate a broad impact of the source, as its unprecedented performance opens the way for new applications.

  • Casimir forces in transmission-line circuits: QED and fluctuation-dissipation formalisms

    Shahmoon E. (2017) Physical Review A.
    It was recently shown that transmission-line waveguides can mediate long-range fluctuation forces between neutral objects, potentially leading to novel Casimir forces in electric circuits. Here we present two approaches for the general description of these forces between electric components embedded in transmission-line circuits. The first, following ordinary quantum electrodynamics (QED), consists of the quantization and scattering theory of voltage and current waves inside transmission lines. The second approach relies on a simple circuit analysis with additional noisy current sources due to resistors in the circuit, as per the fluctuation-dissipation theorem (FDT). We apply the latter approach to derive a general formula for the Casimir force induced by circuit fluctuations between any two impedances. The application of this formula, considering the sign of the resulting force, is discussed. While both QED and FDT approaches are equivalent, we conclude that the latter is simpler to generalize and solve.

  • Self-probing spectroscopy of XUV photo-ionization dynamics in atoms subjected to a strong-field environment

    Azoury D., Kruger M., Orenstein G., Larsson H. R., Bauch S., Bruner B. D. & Dudovich N. (2017) Nature Communications.
    Single-photon ionization is one of the most fundamental light matter interactions in nature, serving as a universal probe of the quantum state of matter. By probing the emitted electron, one can decode the full dynamics of the interaction. When photo-ionization is evolving in the presence of a strong laser field, the fundamental properties of the mechanism can be signicantly altered. Here we demonstrate how the liberated electron can perform a self-probing measurement of such interaction with attosecond precision. Extreme ultraviolet attosecond pulses initiate an electron wavepacket by photo-ionization, a strong infrared field controls its motion, and finally electron-ion collision maps it into re-emission of attosecond radiation bursts. Our measurements resolve the internal clock provided by the self-probing mechanism, obtaining a direct insight into the build-up of photo-ionization in the presence of the strong laser field.

  • The image-forming mirror in the eye of the scallop

    Palmer B. A., Taylor G. J., Brumfeld V., Gur D., Shemesh M., Elad N., Osherov A., Oron D., Weiner S. & Addadi L. (2017) Science.
    Scallops possess a visual system comprising up to 200 eyes, each containing a concave mirror rather than a lens to focus light. The hierarchical organization of the multilayered mirror is controlled for image formation, from the component guanine crystals at the nanoscale to the complex three-dimensional morphology at the millimeter level. The layered structure of the mirror is tuned to reflect the wavelengths of light penetrating the scallop's habitat and is tiled with a mosaic of square guanine crystals, which reduces optical aberrations. The mirror forms images on a double-layered retina used for separately imaging the peripheral and central fields of view. The tiled, off-axis mirror of the scallop eye bears a striking resemblance to the segmented mirrors of reflecting telescopes.

  • Nuclear quantum-assisted magnetometer

    Haeberle T., Oeckinghaus T., Schmid-Lorch D., Pfender M., de Oliveira F. F., Momenzadeh S. A., Finkler A. & Wrachtrup J. (2017) Review of Scientific Instruments.
    Magnetic sensing and imaging instruments are important tools in biological and material sciences. There is an increasing demand for attaining higher sensitivity and spatial resolution, with implementations using a single qubit offering potential improvements in both directions. In this article we describe a scanning magnetometer based on the nitrogen-vacancy center in diamond as the sensor. By means of a quantum-assisted readout scheme together with advances in photon collection efficiency, our device exhibits an enhancement in signal to noise ratio of close to an order of magnitude compared to the standard fluorescence readout of the nitrogen-vacancy center. This is demonstrated by comparing non-assisted and assisted methods in a T<sub>1</sub> relaxation time measurement.

  • Observing Dissipative Topological Defects with Coupled Lasers

    Pal V., Tradonsky C., Chriki R., Friesem A. & Davidson N. (2017) Physical review letters.
    Topological defects have been observed and studied in a wide range of systems, such as cosmology, spin systems, cold atoms, and optics, as they are quenched across a phase transition into an ordered state. These defects limit the coherence of the system and its ability to approach a fully ordered state, so revealing their origin and control is becoming an increasingly important field of research. We observe dissipative topological defects in a one-dimensional ring of phased-locked lasers, and show how their formation is related to the Kibble-Zurek mechanism and is governed in a universal manner by two competing time scales. The ratio between these two time scales depends on the system parameters, and thus offers the possibility of enabling the system to dissipate to a fully ordered, defect-free state that can be exploited for solving hard computational problems in various fields.

  • Phase retrieval in multicore fiber bundles

    Kogan D., Sivankutty S., Tsvirkun V., Bouwmans G., Andresen E. R., Rigneault H. & Oron D. (2017) Optics Letters.
    Multicore fiber bundles are widely used in endoscopy due to their miniature size and their direct imaging capabilities. They have recently been used, in combination with spatial light modulators, in various realizations of endoscopy with little or no optics at the distal end. These schemes require characterization of the relative phase offsets between the different cores, typically done using off-axis holography, thus requiring both an interferometric setup and, typically, access to the distal tip. Here we explore the possibility of employing phase retrieval to extract the necessary phase information. We show that in the noise-free case, disordered fiber bundles are superior for phase retrieval over their periodic counterparts, and demonstrate experimentally accurate retrieval of phase information for up to 10 simultaneously illuminated cores. Thus, phase retrieval is presented as a viable alternative for real-timemonitoring of phase distortions in multicore fiber bundles. (C) 2017 Optical Society of America

  • Composite functional metasurfaces for multispectral achromatic optics

    Avayu O., Almeida E., Prior Y. & Ellenbogen T. (2017) Nat Commun.
    Nanostructured metasurfaces offer unique capabilities for subwavelength control of optical waves. Based on this potential, a large number of metasurfaces have been proposed recently as alternatives to standard optical elements. In most cases, however, these elements suffer from large chromatic aberrations, thus limiting their usefulness for multiwavelength or broadband applications. Here, in order to alleviate the chromatic aberrations of individual diffractive elements, we introduce dense vertical stacking of independent metasurfaces, where each layer is made from a different material, and is optimally designed for a different spectral band. Using this approach, we demonstrate a triply red, green and blue achromatic metalens in the visible range. We further demonstrate functional beam shaping by a self-aligned integrated element for stimulated emission depletion microscopy and a lens that provides anomalous dispersive focusing. These demonstrations lead the way to the realization of ultra-thin superachromatic optical elements showing multiple functionalities- all in a single nanostructured ultra-thin element.

  • Fast Dynamical Decoupling of the Molmer-Sorensen Entangling Gate

    Manovitz T., Rotem A., Shaniv R., Cohen I., Shapira Y., Akerman N., Retzker A. & Ozeri R. (2017) Physical Review Letters.
    Engineering entanglement between quantum systems often involves coupling through a bosonic mediator, which should be disentangled from the systems at the operation's end. The quality of such an operation is generally limited by environmental and control noise. One of the prime techniques for suppressing noise is by dynamical decoupling, where one actively applies pulses at a rate that is faster than the typical time scale of the noise. However, for boson-mediated gates, current dynamical decoupling schemes require executing the pulses only when the boson and the quantum systems are disentangled. This restriction implies an increase of the gate time by a factor of root N, with N being the number of pulses applied. Here we propose and realize a method that enables dynamical decoupling in a boson-mediated system where the pulses can be applied while spin-boson entanglement persists, resulting in an increase in time that is at most a factor of pi/2, independently of the number of pulses applied. We experimentally demonstrate the robustness of our entangling gate with fast dynamical decoupling to sigma(z) noise using ions in a Paul trap.

  • Probing atomic Higgs-like forces at the precision frontier

    Delaunay C., Ozeri R., Perez G. & Soreq Y. (2017) Physical Review D.
    We propose a novel approach to probe new fundamental interactions using isotope shift spectroscopy in atomic clock transitions. As a concrete toy example we focus on the Higgs boson couplings to the building blocks of matter: the electron and the up and down quarks. We show that the attractive Higgs force between nuclei and their bound electrons, which is poorly constrained, might induce effects that are larger than the current experimental sensitivities. More generically, we discuss how new interactions between the electron and the neutrons, mediated via light new degrees of freedom, may lead to measurable nonlinearities in a King plot comparison between isotope shifts of two different transitions. Given state-of-the-art accuracy in frequency comparison, isotope shifts have the potential to be measured with sub-Hz accuracy, thus potentially enabling the improvement of current limits on new fundamental interactions. A candidate atomic system for this measurement requires two different clock transitions and four zero nuclear spin isotopes. We identify several systems that satisfy this requirement and also briefly discuss existing measurements. We consider the size of the effect related to the Higgs force and the requirements for it to produce an observable signal.

  • Strain-Induced Type II Band Alignment Control in CdSe Nanoplatelet/ZnS-Sensitized Solar Cells

    Luo S., Kazes M., Lin H. & Oron D. (2017) Journal of Physical Chemistry C.
    Colloidal CdSe nanoplatelets (NPLs) deposited on TiO<sub>2</sub> and overcoated by ZnS were explored as light absorbers in semiconductor-sensitized solar cells (SSSCs). Significant red shifts of both absorption and steady-state photoluminescence (PL) along with rapid PL quenching suggest a type II band alignment at the interface of the CdSe NPL and the ZnS barrier layer grown on the NPL layer, as confirmed by energy band measurements. The considerable red shift leads to enhanced spectral absorption coverage. Cell characterization shows an increased open-circuit voltage of 664 mV using a polysulfide electrolyte, which can be attributed to a photoinduced dipole effect created by the spatial charge separation across the nanoplatelet sensitizers. The observed short-circuit current density of 11.14 mA cm<sup>-2</sup> approaches the maximal theoretical current density for this choice of absorber, yielding an internal quantum efficiency of close to 100%, a clear signature of excellent charge transport and collection yields. With their steep absorption onset and negligible inhomogeneous broadening, NPL-based SSSCs are intriguing candidates for future high-voltage sensitized cells.

  • Digital Degenerate Cavity Laser

    Tradonsky C., Chriki R., Barach G., Pal V., Friesem A. A. & Davidson N. (2017) .
    In the past, we investigated degenerate cavity lasers (DCL) which allows manipulation of both near-field and far-field properties of the output beam. The DCL was comprised of a gain medium, two lenses in a 4f telescope configuration, an output coupler at one end and a back mirror at the other end. With the DCL we investigated topological defects in arrays of coupled lasers[1, simulation of classical spins arrays in a frustrated geometry[2, beam focusing after scattering media[3, and lasers with controllable coherence functions for speckles reduction[4. In these investigations, the DCL usually included metallic masks of holes and filters that had to be specifically designed and fabricated for each application.

  • On the 2D Phase Retrieval Problem

    Kogan D., Eldar Y. C. & Oron D. (2017) IEEE Transactions on Signal Processing.
    The recovery of a signal from the magnitude of its Fourier transform, also known as phase retrieval, is of fundamental importance in many scientific fields. It is well known that due to the loss of Fourier phase the problem in one-dimensional (1D) is ill-posed. Without further constraints, there is no unique solution to the problem. In contrast, uniqueness up to trivial ambiguities very often exists in higher dimensions, with mild constraints on the input. In this paper, we focus on the 2D phase retrieval problem and provide insight into this uniqueness property by exploring the connection between the 2D and 1D formulations. In particular, we show that 2D phase retrieval can be cast as a 1D problem with additional constraints, which limit the solution space. We then prove that only one additional constraint is sufficient to reduce the many feasible solutions in the 1D setting to a unique solution for almost all signals. These results allow to obtain an analytical approach (with combinatorial complexity) to solve the 2D phase retrieval problem when it is unique.

  • Plasmonic coupling in metal nanocavities

    Sain B., Kaner R., Bondy Y. & Prior Y. (2017) .
    Optical Fabry-Perot like modes, situated diagonally as a function the gap, are observed in transmission through pairs of coupled nanocavities in gold film, while plasmonic wakes are observed from a linear array of individual cavities.

  • Third-order-harmonic generation in coherently spinning molecules

    Prost E., Zhang H., Hertz E., Billard F., Lavorel B., Bejot P., Zyss J., Averbukh I. S. & Faucher O. (2017) Physical Review A.
    The rotational Doppler effect occurs when circularly polarized light interacts with a rotating anisotropic material. It is manifested by the appearance of a spectral shift ensuing from the transfer of angular momentum and energy between radiation and matter. Recently, we reported terahertz-range rotational Doppler shifts produced in third-order nonlinear optical conversion [O. Faucher et al., Phys. Rev. A 94, 051402(R) (2016)]. The experiment was performed in an ensemble of coherently spinning molecules prepared by a short laser pulse exhibiting a twisted linear polarization. The present work provides an extensive analysis of the rotational Doppler effect in third-order-harmonic generation from spinning linear molecules. The underlying physics is investigated both experimentally and theoretically. The implication of the rotational Doppler effect in higher-order processes like high-order-harmonic generation is discussed.

  • Colloquium: Strongly interacting photons in one-dimensional continuum

    Roy D., Wilson C. M. & Firstenberg O. (2017) Reviews of Modern Physics.
    Photon-photon scattering in vacuum is extremely weak. However, strong effective interactions between single photons can be realized by employing strong light-matter coupling. These interactions are a fundamental building block for quantum optics, bringing many-body physics to the photonic world and providing important resources for quantum photonic devices and for optical metrology. This Colloquium reviews the physics of strongly interacting photons in one-dimensional systems with no optical confinement along the propagation direction. It focuses on two recently demonstrated experimental realizations: superconducting qubits coupled to open transmission lines and interacting Rydberg atoms in a cold gas. Advancements in the theoretical understanding of these systems are presented in complementary formalisms and compared to experimental results. The experimental achievements are summarized alongside a description of the quantum optical effects and quantum devices emerging from them.

  • Stable multi-GeV electron accelerator driven by waveform-controlled PW laser pulses

    Kim H. T., Pathak V. B., Pae K. H., Lifschitz A., Sylla F., Shin J. H., Hojbota C., Lee S. K., Sung J. H., Lee H. W., Guillaume E., Thaury C., Nakajima K., Vieira J., Silva L. O., Malka V. & Nam C. H. (2017) Scientific Reports.
    The achievable energy and the stability of accelerated electron beams have been the most critical issues in laser wakefield acceleration. As laser propagation, plasma wave formation and electron acceleration are highly nonlinear processes, the laser wakefield acceleration (LWFA) is extremely sensitive to initial experimental conditions. We propose a simple and elegant waveform control method for the LWFA process to enhance the performance of a laser electron accelerator by applying a fully optical and programmable technique to control the chirp of PW laser pulses. We found sensitive dependence of energy and stability of electron beams on the spectral phase of laser pulses and obtained stable 2-GeV electron beams from a 1-cm gas cell of helium. The waveform control technique for LWFA would prompt practical applications of centimeter-scale GeV-electron accelerators to a compact radiation sources in the x-ray and gamma-ray regions.

  • Quantum Light in Curved Low Dimensional Hexagonal Boron Nitride Systems

    Chejanovsky N., Kim Y., Zappe A., Stuhlhofer B., Taniguchi T., Watanabe K., Dasari D., Finkler A., Smet J. H. & Wrachtrup J. (2017) Scientific Reports.
    Low-dimensional wide bandgap semiconductors open a new playing field in quantum optics using sub-bandgap excitation. In this field, hexagonal boron nitride (h-BN) has been reported to host single quantum emitters (QEs), linking QE density to perimeters. Furthermore, curvature/perimeters in transition metal dichalcogenides (TMDCs) have demonstrated a key role in QE formation. We investigate a curvature-Abundant BN system-quasi one-dimensional BN nanotubes (BNNTs) fabricated via a catalyst-free method. We find that non-Treated BNNT is an abundant source of stable QEs and analyze their emission features down to single nanotubes, comparing dispersed/suspended material. Combining high spatial resolution of a scanning electron microscope, we categorize and pin-point emission origin to a scale of less than 20 nm, giving us a one-To-one validation of emission source with dimensions smaller than the laser excitation wavelength, elucidating nano-Antenna effects. Two emission origins emerge: hybrid/entwined BNNT. By artificially curving h-BN flakes, similar QE spectral features are observed. The impact on emission of solvents used in commercial products and curved regions is also demonstrated. The 'out of the box' availability of QEs in BNNT, lacking processing contamination, is a milestone for unraveling their atomic features. These findings open possibilities for precision engineering of QEs, puts h-BN under a similar 'umbrella' of TMDC's QEs and provides a model explaining QEs spatial localization/formation using electron/ion irradiation and chemical etching.

  • Crystallographic Mapping of Guided Nanowires by Second Harmonic Generation Polarimetry

    Neeman L., Ben-Zvi R., Rechav K., Popovitz-Biro R., Oron D. & Joselevich E. (2017) Nano Letters.
    The growth of horizontal nanowires (NWs) guided by epitaxial and graphoepitaxial relations with the substrate is becoming increasingly attractive owing to the possibility of controlling their position, direction, and crystallographic orientation. In guided NWs, as opposed to the extensively characterized vertically grown NWs, there is an increasing need for understanding the relation between structure and properties, specifically the role of the epitaxial relation with the substrate. Furthermore, the uniformity of crystallographic orientation along guided NWs and over the substrate has yet to be checked. Here we perform highly sensitive second harmonic generation (SHG) polarimetry of polar and nonpolar guided ZnO NWs grown on R-plane and M-plane sapphire. We optically map large areas on the substrate in a nondestructive way and find that the crystallographic orientations of the guided NWs are highly selective and specific for each growth direction with respect to the substrate lattice. In addition, we perform SHG polarimetry along individual NWs and find that the crystallographic orientation is preserved along the NW in both polar and nonpolar NWs. While polar NWs show highly uniform SHG along their axis, nonpolar NWs show a significant change in the local nonlinear susceptibility along a few micrometers, reflected in a reduction of 40% in the ratio of the SHG along different crystal axes. We suggest that these differences may be related to strain accumulation along the nonpolar wires. We find SHG polarimetry to be a powerful tool to study both selectivity and uniformity of crystallographic orientations of guided NWs with different epitaxial relations.

  • Grazing-incidence optical magnetic recording with super-resolution

    Scheunert G., Cohen S., Kullock R., McCarron R., Rechev K., Kaplan-Ashiri I., Bitton O., Dawson P., Hecht B. & Oron D. (2017) Beilstein Journal of Nanotechnology.
    Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ<sub>0</sub>H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface - six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features - thus suggesting full compatibility with NFT-HAMR.

  • Isolating strong-field dynamics in molecular systems

    Orenstein G., Pedatzur O., Uzan A. J., Bruner B. D., Mairesse Y. & Dudovich N. (2017) Physical Review A.
    Strong-field ionization followed by recollision provides a unique pump-probe measurement which reveals a range of electronic processes, combining sub-Angstrom spatial and attosecond temporal resolution. A major limitation of this approach is imposed by the coupling between the spatial and temporal degrees of freedom. In this paper we focus on the study of high harmonic generation and demonstrate the ability to isolate the internal dynamics - decoupling the temporal information from the spatial one. By applying an in situ approach we reveal the universality of the intrinsic pump-probe measurement and establish its validity in molecular systems. When several orbitals are involved we identify the fingerprint of the transition from the single-channel case into the multiple-channel dynamics, where complex multielectron phenomena are expected to be observed.

  • Generation of high pressures by short-pulse low-energy laser irradiation

    Jakubowska K., Batani D., Feugeas J. -., Forestier-Colleoni P., Hulin S., Nicolai P., Santos J. J., Flacco A., Vauzour B. & Malka V. (2017) EPL.
    The goal of this paper is twofold: first, we demonstrate shock generation with ultra-short (24 fs) and low-energy (J) laser pulse, following the energy deposition in the target by fast electrons; second, we show that such shocks can be used to provide information on compressed matter. For a target with 50 mu m thickness we have clearly inferred the formation of a shock wave with pressure >= 100 Mbar. We have also measured the color temperature of the emitting target rear side at breakout time (T approximate to 0.6 eV), which is in good agreement with predictions from equation-of-state models (SESAME tables) and hydrodynamic simulations.

  • Catalysis of heat-to-work conversion in quantum machines

    Ghosh A., Latune C. L., Davidovich L. & Kurizki G. (2017) Proceedings Of The National Academy Of Sciences Of The United States Of America-Physical Sciences.
    We propose a hitherto-unexplored concept in quantum thermodynamics: catalysis of heat-to-work conversion by quantum nonlinear pumping of the piston mode which extracts work from the machine. This concept is analogous to chemical reaction catalysis: Small energy investment by the catalyst (pump) may yield a large increase in heat-to-work conversion. Since it is powered by thermal baths, the catalyzed machine adheres to the Carnot bound, but may strongly enhance its efficiency and power compared with its noncatalyzed counterparts. This enhancement stems from the increased ability of the squeezed piston to store work. Remarkably, the fraction of piston energy that is convertible into work may then approach unity. The present machine and its counterparts powered by squeezed baths share a common feature: Neither is a genuine heat engine. However, a squeezed pump that catalyzes heat-to-work conversion by small investment of work is much more advantageous than a squeezed bath that simply transduces part of the work invested in its squeezing into work performed by the machine.

  • Intra-cavity spin controlled geometric phase metasurface

    Chriki R., Maguid E., Tradonsky C., Kleiner V., Friesem A. A., Davidson N. & Hasman E. (2017) .

  • Intra-cavity spin controlled geometric phase metasurface

    Chriki R., Maguid E., Tradonsky C., Kleiner V., Friesem A. A., Davidson N. & Hasman E. (2017) .

  • Nucleation, Growth, and Structural Transformations of Perovskite Nanocrystals

    Udayabhaskararao T., Kazes M., Houben L., Lin H. & Oron D. (2017) Chemistry of Materials.
    Despite the recent surge of interest in lead halide perovskite nanocrystals, there are still significant gaps in the understanding of nucleation and growth processes involved in their formation. Using CsPbX3 as a model system, we systematically study the formation mechanism of cubic CsPbX3 nanocrystals, their growth via oriented attachment into larger nanostructures, and the associated phase transformations. We found evidence to support that the formation of CsPbX3 NCs occurs through the seed-mediated nucleation method, where Pb-o NPs formed during the course of reaction act as seeds. Further growth occurs through self-assembly and oriented attachment. The polar environment is a major factor in determining the structure and shape of the resulting nanoparticles, as confirmed by experiments with aged seed reaction mixtures, and by addition of polar additives. These results provide a fundamental understanding of the influence of the environment polarity on self-assembly, self-healing, and the ability to control the morphology and structure over the perovskite structures. As a result of this understanding, we were able to extend the synthesis to produce other materials such as CsPbBr3 nanowires and orthorhombic CsPbI3 nanowires with tunable length ranging from 200 nm to several microns.

  • Rotated echoes of molecular alignment: fractional, high order and imaginary

    Lin K., Ma J., Gong X., Song Q., Ji Q., Zhang W., Li H., Lu P., Li H., Zeng H., Wu J., Hartmann J., Faucher O., Gershnabel E., Prior Y. & Averbukh I. S. (2017) Optics Express.
    We report experimental observations of rotated echoes of alignment induced by a pair of time-delayed and polarization-skewed femtosecond laser pulses interacting with an ensemble of molecular rotors. Rotated fractional echoes, rotated high order echoes and rotated imaginary echoes are directly visualized by using the technique of coincident Coulomb explosion imaging. We show that the echo phenomenon not only exhibits temporal recurrences but also spatial rotations determined by the polarization of the time-delayed second pulse. The dynamics of echo formation is well described by the laser-induced filamentation in rotational phase space. The quantum-mechanical simulation shows good agreements with the experimental results.

  • Numerical studies of density transition injection in laser wakefield acceleration

    Massimo F., Lifschitz A. F., Thaury C. & Malka V. (2017) Plasma Physics and Controlled Fusion.
    The quality of laser wakefield accelerated electrons beams is strongly determined by the physical mechanism exploited to inject electrons in the wakefield. One of the techniques used to improve the beam quality is the density transition injection, where the electron trapping occurs as the laser pulse passes a sharp density transition created in the plasma. Although this technique has been widely demonstrated experimentally, the literature lacks theoretical and numerical studies on the effects of all the transition parameters. We thus report and discuss the results of a series of particle in cell (PIC) simulations where the density transition height and downramp length are systematically varied, to show how the electron beam parameters and the injection mechanism are affected by the density transition parameters.

  • Cooperative Resonances in Light Scattering from Two-Dimensional Atomic Arrays

    Shahmoon E., Wild D. S., Lukin M. D. & Yelin S. F. (2017) Physical Review Letters.
    We consider light scattering off a two-dimensional (2D) dipolar array and show how it can be tailored by properly choosing the lattice constant of the order of the incident wavelength. In particular, we demonstrate that such arrays can operate as a nearly perfect mirror for a wide range of incident angles and frequencies, and shape the emission pattern from an individual quantum emitter into a well-defined, collimated beam. These results can be understood in terms of the cooperative resonances of the surface modes supported by the 2D array. Experimental realizations are discussed, using ultracold arrays of trapped atoms and excitons in 2D semiconductor materials, as well as potential applications ranging from atomically thin metasurfaces to single photon nonlinear optics and nanomechanics.

  • Analysis of deterministic swapping of photonic and atomic states through single-photon Raman interaction

    Rosenblum S., Borne A. & Dayan B. (2017) Physical Review A.
    The long-standing goal of deterministic quantum interactions between single photons and single atoms was recently realized in various experiments. Among these, an appealing demonstration relied on single-photon Raman interaction (SPRINT) in a three-level atom coupled to a single-mode waveguide. In essence, the interference-based process of SPRINT deterministically swaps the qubits encoded in a single photon and a single atom, without the need for additional control pulses. It can also be harnessed to construct passive entangling quantum gates, and can therefore form the basis for scalable quantum networks in which communication between the nodes is carried out only by single-photon pulses. Here we present an analytical and numerical study of SPRINT, characterizing its limitations and defining parameters for its optimal operation. Specifically, we study the effect of losses, imperfect polarization, and the presence of multiple excited states. In all cases we discuss strategies for restoring the operation of SPRINT.

  • Single-shot energy measurement of a single atom and the direct reconstruction of its energy distribution

    Meir Z., Sikorsky T., Akerman N., Ben Shlomi R., Pinkas M. & Ozeri R. (2017) Physical Review A.
    An ensemble of atoms in a steady state, whether or not in thermal equilibrium, has a well-defined energy distribution. Since the energy of single atoms within the ensemble cannot be individually measured, energy distributions are typically inferred from statistical averages. Here, we show how to measure the energy of a single atom in a single experimental realization (single shot). The energy distribution of the atom over many experimental realizations can thus be readily and directly obtained. We apply this method to a single ion trapped in a linear Paul trap for which the energy measurement in a single shot is applicable from 10 K×kB and above. Our energy measurement agrees within 5% to a different thermometry method which requires extensive averaging. Apart from the total energy, we also show that the motion of the ion in different trap modes can be distinguished. We believe that this method will have profound implications on single-particle chemistry and collision experiments.

  • Vertically aligned ZnO/ZnTe core/shell heterostructures on an AZO substrate for improved photovoltaic performance

    Luo S., He X., Shen H., Li J., Yin X., Oron D. & Lin H. (2017) RSC Advances.
    Vertically aligned ZnO/ZnTe core/shell heterostructures on an Al-doped ZnO substrate are developed for non-toxic semiconductor sensitized solar cells. Structural and morphological analysis serves as evidence of the successful synthesis of ZnO nanorods, ZnTe nanocrystals and ZnO/ZnTe heterostructures. The clearly observed quenching of photoluminescence (PL) from the heterostructure indicates efficient charge transfer occurring at the interface of ZnO and ZnTe, due to the type-II energy level alignment constructed by the two. The formation mechanism of the ZnO/ZnTe heterostructure is studied in depth via time-dependent reactions. It was found that the strain between ZnO and ZnTe modifies the band alignment at the interface of the heterostructure in a manner which depends on the growth time. Finally, sensitized solar cells based on the ZnO/ZnTe heterostructures with different ZnTe growth times were fabricated to evaluate the photovoltaic performance. By the careful control of the ZnTe growth time and as a result of the band alignment between ZnO and ZnTe, the power conversion efficiency (PCE) of the vertically aligned ZnO/ZnTe based solar cells could be improved to about 2%, along with a short-circuit photocurrent density of around 7.5 mA cm (-2), a record efficiency for ZnO/ZnTe based sensitized solar cells. Notably, for the optimized system the internal quantum efficiency of the ZnO/ZnTe based solar cell approaches 100% in certain wavelengths, implying effective separation of photoexcited free carriers towards either the electrolyte or anode.

  • Casimir stress inside planar materials

    Griniasty I. & Leonhardt U. (2017) Physical Review A.
    The Casimir force between macroscopic bodies is well understood, but not the Casimir force inside bodies. Guided by a physically intuitive picture, we develop the macroscopic theory of the renormalized Casimir stress inside planar materials (where the electromagnetic properties vary in one direction). Our theory may be applied in predicting how inhomogeneous fluids respond to Casimir forces.

  • Enhancing the Performance of Perovskite Solar Cells by Hybridizing SnS Quantum Dots with CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>

    Han J., Yin X., Nan H., Zhou Y., Yao Z., Li J., Oron D. & Lin H. (2017) Small.
    The combination of perovskite solar cells and quantum dot solar cells has significant potential due to the complementary nature of the two constituent materials. In this study, solar cells (SCs) with a hybrid CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/SnS quantum dots (QDs) absorber layer are fabricated by a facile and universal in situ crystallization method, enabling easy embedding of the QDs in perovskite layer. Compared with SCs based on CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, SCs using CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/SnS QDs hybrid films as absorber achieves a 25% enhancement in efficiency, giving rise to an efficiency of 16.8%. The performance improvement can be attributed to the improved crystallinity of the absorber, enhanced photo-induced carriers' separation and transport within the absorber layer, and improved incident light utilization. The generality of the methods used in this work paves a universal pathway for preparing other perovskite/QDs hybrid materials and the synthesis of entire nontoxic perovskite/QDs hybrid structure.

  • Spectroscopic measurement of the softness of ultracold atomic collisions

    Coslovsky J., Afek G., Mil A., Almog I. & Davidson N. (2017) Physical Review A.
    The softness of elastic atomic collisions, defined as the average number of collisions each atom undergoes until its energy decorrelates significantly, can have a considerable effect on the decay dynamics of atomic coherence. In this paper we combine two spectroscopic methods to measure these dynamics and obtain the collisional softness of ultracold atoms in an optical trap: Ramsey spectroscopy to measure the energy decorrelation rate and echo spectroscopy to measure the collision rate. We obtain a value of 2.5(3) for the collisional softness, in good agreement with previously reported numerical molecular-dynamics simulations. This fundamental quantity is used to determine the s-wave scattering lengths of different atoms but has not been directly measured. We further show that the decay dynamics of the revival amplitudes in the echo experiment has a transition in its functional decay. The transition time is related to the softness of the collisions and provides yet another way to approximate it. These conclusions are supported by Monte Carlo simulations of the full echo dynamics. The methods presented here can allow measurement of a generalized softness parameter for other two-level quantum systems with discrete spectral fluctuations.

  • Multilayered metamaterials for functional light control

    Almeida E., Avayu O., Ellenbogen T. & Prior Y. (2017) .
    We demonstrate composite, multiplexed 3D metamaterials for functional light manipulation. Applications include multi-wavelength achromatic metalenses in the visible spectral range, integrated elements for STED microscopy, and nonlinear holography. Prospects for novel applications are discussed.

  • Demonstration of deterministic and passive photon-atom SWAP quantum gate

    Borne A., Bechler O., Rosenblum S., Guendelman G., Mor O., Netzer M., Gurovich D., Ohana T., Aqua Z., Drucker N., Lovsky Y., Bruch R., Finkelstein R., Shafir E. & Dayan B. (2017) .
    Using single-photon Raman interaction, we demonstrate a deterministic and passive SWAP gate and quantum memory between the states of a single photon and a single <sup>87</sup>Rb atom coupled to high-Q microresonator.

  • Phase-controlled propagation of surface plasmons

    Sain B., Kaner R. & Prior Y. (2017) Light: Science and Applications.
    Directional emission of electromagnetic radiation can be achieved using a properly shaped single antenna or a phased array of individual antennas. Control of the individual phases within an array enables scanning or other manipulations of the emission, and it is this property of phased arrays that makes them attractive in modern systems. Likewise, the propagation of surface plasmons at the interface between metal films and dielectric materials can be determined by shaping the individual surface nanostructures or via the phase control of individual elements in an array of such structures. Here, we demonstrate control of the propagation of surface plasmons within a linear array of nanostructures. The generic situation of plasmonic surface propagation that is different on both sides of a metal film provides a unique opportunity for such control: plasmons propagating on the slower side feed into the side with the faster propagation, creating a phased array of interfering antennas and thus controlling the directionality of the wake fields. We further show that by shaping the individual nanoantennas, we can generate an asymmetric propagation geometry.

  • Wavepacket revivals via complex trajectory propagation

    Koch W. & Tannor D. (2017) Chemical Physics Letters.
    Complex-valued semiclassical methods hold out the promise of treating classically allowed and classically forbidden processes on the same footing. In addition, they provide a natural way to describe optical excitation with complex fields within the trajectory framework. Despite their promise, these methods have until now been limited to short time propagation, due to the numerical difficulties introduced by the complexification. Using a new Final Value Representation of the Coherent State Propagator (FINCO), combined with an analysis of the complex classical phase space, we achieve accurate wavepacket propagation all the way to the revival time of a strongly anharmonic system.

  • Optimization of nonlinear optical processes in arrays of metallic nanocavities

    Blechman Y., Almeida E. & Prior Y. (2017) .
    We challenge the conventional wisdom that enhancement of nonlinear optical processes in plasmonic nanomaterials can be fully predicted by their linear properties.

  • Electron heating by intense short-pulse lasers propagating through near-critical plasmas

    Debayle A., Mollica F., Vauzour B., Wan Y., Flacco A., Malka V., Davoine X. & Gremillet L. (2017) New Journal of Physics.
    We investigate the electron heating induced by a relativistic-intensity laser pulse propagating through a near-critical plasma. Using particle-in-cell simulations, we show that a specific interaction regime sets in when, due to the energy depletion caused by the plasma wakefield, the laser front profile has steepened to the point of having a length scale close to the laser wavelength. Wave breaking and phase mixing have then occurred, giving rise to a relativistically hot electron population following the laser pulse. This hot electron flow is dense enough to neutralize the cold bulk electrons during their backward acceleration by the wakefield. This neutralization mechanism delays, but does not prevent the breaking of the wakefield: the resulting phase mixing converts the large kinetic energy of the backward-flowing electrons into thermal energy greatly exceeding the conventional ponderomotive scaling at laser intensities >10(21) W cm(-2) and gas densities around 10% of the critical density. We develop a semi-numerical model, based on the Akhiezer-Polovin equations, which correctly reproduces the particle-in-cell-predicted electron thermal energies over a broad parameter range. Given this good agreement, we propose a criterion for full laser absorption that includes field-induced ionization. Finally, we show that our predictions still hold in a two-dimensional geometry using a realistic gas profile.

  • Digital degenerate cavity laser

    Tradonsky C., Chriki R., Barach G., Pal V., Friesem A. A. & Davidson N. (2017) .

  • Talbot diffraction and Fourier filtering for phase locking an array of lasers

    Tradonsky C., Pal V., Chriki R., Davidson N. & Friesem A. A. (2017) Applied Optics.
    Talbot diffraction, together with Fourier filtering, are incorporated into a degenerate laser cavity to demonstrate efficient and controlled phase locking of hundreds of coupled lasers formed in different geometries and having different phase distributions. Such a combined approach leads to higher efficiency, better control, and greater variety of output phase distributions than would be possible with either separately. Simulated and experimental results for square, triangular, and honeycomb laser array geometries are presented.

  • Quantum correlation enhanced super-resolution localization microscopy enabled by a fibre bundle camera

    Israel Y., Tenne R., Oron D. & Silberberg Y. (2017) Nature Communications.
    Despite advances in low-light-level detection, single-photon methods such as photon correlation have rarely been used in the context of imaging. The few demonstrations, for example of subdiffraction-limited imaging utilizing quantum statistics of photons, have remained in the realm of proof-of-principle demonstrations. This is primarily due to a combination of low values of fill factors, quantum efficiencies, frame rates and signal-to-noise characteristic of most available single-photon sensitive imaging detectors. Here we describe an imaging device based on a fibre bundle coupled to single-photon avalanche detectors that combines a large fill factor, a high quantum efficiency, a low noise and scalable architecture. Our device enables localization-based super-resolution microscopy in a non-sparse non-stationary scene, utilizing information on the number of active emitters, as gathered from non-classical photon statistics.

  • Dynamic decoupling in the presence of colored control noise

    Almog I., Loewenthal G., Coslovsky J., Sagi Y. & Davidson N. (2016) Physical Review A.
    An optimal dynamic decoupling of a quantum system coupled to a noisy environment must take into account also the imperfections of the control pulses. We present a formalism which describes, in a closed-form expression, the evolution of the system, including the spectral function of both the environment and control noise. We show that by measuring these spectral functions, our expression can be used to optimize the decoupling pulse sequence. We demonstrate this approach with an ensemble of optically trapped ultracold rubidium atoms, and use quantum process tomography to identify the effect of the environment and control noise. Our approach is applicable and important for any realistic implementation of quantum information processing.

  • Exciting Molecules Close to the Rotational Quantum Resonance: Anderson Wall and Rotational Bloch Oscillations

    Floss J. & Averbukh I. S. (2016) Journal of Physical Chemistry A.
    We describe a universal behavior of linear molecules excited by a periodic train of short laser pulses under conditions close to the quantum resonance. The quantum resonance effect causes an unlimited ballistic growth of the angular momentum. We show that a disturbance of the quantum resonance, either by the centrifugal distortion of the rotating molecules or a controlled detuning of the pulse train period from the so-called rotational revival time, eventually halts the growth by causing Anderson localization beyond a critical value of the angular momentum, the Anderson wall. Below the wall, the rotational excitation oscillates with the number of pulses due to a mechanism similar to Bloch oscillations in crystalline solids. We suggest optical experiments capable of observing the rotational Anderson wall and Bloch oscillations at near-ambient conditions with the help of existing laser technology.

  • Efficient molecular quantum dynamics in coordinate and phase space using pruned bases

    Larsson H. R., Hartke B. & Tannor D. (2016) JOURNAL OF CHEMICAL PHYSICS.
    We present an efficient implementation of dynamically pruned quantum dynamics, both in coordinate space and in phase space. We combine the ideas behind the biorthogonal von Neumann basis (PvB) with the orthogonalized momentum-symmetrized Gaussians (Weylets) to create a newbasis, projected Weylets, that takes the best from both methods. We benchmark pruned time-dependent dynamics using phase-space-localized PvB, projectedWeylets, and coordinate-space-localized DVR bases, with real-world examples in up to six dimensions. For the examples studied, coordinate-space localization is the most important factor for efficient pruning and the pruned dynamics is much faster than the unpruned, exact dynamics. Phase-space localization is useful for more demanding dynamics where many basis functions are required. There, projected Weylets offer a more compact representation than pruned DVR bases. Published by AIP Publishing.

  • 3D printing of gas jet nozzles for laser-plasma accelerators

    Dopp A., Guillaume E., Thaury C., Gautier J., Phuoc K. T. & Malka V. (2016) Review of Scientific Instruments.
    Recent results on laser wakefield acceleration in tailored plasma channels have underlined the importance of controlling the density profile of the gas target. In particular, it was reported that the appropriate density tailoring can result in improved injection, acceleration, and collimation of laser-accelerated electron beams. To achieve such profiles, innovative target designs are required. For this purpose, we have reviewed the usage of additive layer manufacturing, commonly known as 3D printing, in order to produce gas jet nozzles. Notably we have compared the performance of two industry standard techniques, namely, selective laser sintering (SLS) and stereolithography (SLA). Furthermore we have used the common fused deposition modeling to reproduce basic gas jet designs and used SLA and SLS for more sophisticated nozzle designs. The nozzles are characterized interferometrically and used for electron acceleration experiments with the SALLE JAUNE terawatt laser at Laboratoire d'Optique Appliquee. 

  • Atomic quadrupole moment measurement using dynamic decoupling

    Shaniv R., Akerman N. & Ozeri R. (2016) Physical review letters.
    We present a method that uses dynamic decoupling of a multilevel quantum probe to distinguish small frequency shifts that depend on mj2, where mj2 is the angular momentum of level |j| along the quantization axis, from large noisy shifts that are linear in mj, such as those due to magnetic field noise. Using this method we measured the electric-quadrupole moment of the 4D5/2 level in Sr+88 to be 2.973-0.033+0.026ea02. Our measurement improves the uncertainty of this value by an order of magnitude and thus helps mitigate an important systematic uncertainty in Sr+88 based optical atomic clocks and verifies complicated many-body quantum calculations.

  • Charge Transfer Dynamics in CdS and CdSe@CdS Based Hybrid Nanorods Tipped with Both PbS and Pt

    Rukenstein P., Teitelboim A., Volokh M., Diab M., Oron D. & Mokari T. (2016) Journal of Physical Chemistry C.
    The synthesis of hybrid nanostructures that have specific properties has become a significant topic for construction of "smart" nanomaterials for various applications. Formation of hybrid nanostructures, particularly those combining metals and semiconductors, often introduces new chemical, optical, and electronic properties. Here, we show a simple solution phase synthesis of multicomponent heterostructures based on the growth of metal and semiconductor onto the tips of semiconductor nanorods, leading to the formation of a hybrid semiconductor/semiconductor/metal structure. The synthesis involves the reduction of Pt-acetylacetonate to achieve selective growth of a Pt metal tip onto one side of the CdS rod, followed by the thermal decomposition of Pb-bis(diethyldithiocarbamate) to grow a PbS nanocrystal onto the other tip of the nanorod. The band alignment between the two semiconductor components as well as the alignment with the Fermi level of the metal could support intraparticle charge transfer, which is often sought after for photocatalysis applications. Yet, we show, using femtosecond transient differential absorption spectroscopy (TDA), that carrier dynamics in such a hybrid system can be more complex than that predicted simply by bulk band alignment considerations. This highlights the importance of the design of band alignment and interface passivation and its role in affecting carrier dynamics within hybrid nanostructures.

  • Multiatom quantum coherences in micromasers as fuel for thermal and nonthermal machines

    Dağ C. B., Niedenzu W., Müstecaplioğlu Ö. E. & Kurizki G. (2016) Entropy.
    In this paper, we address the question: To what extent is the quantum state preparation of multiatom clusters (before they are injected into the microwave cavity) instrumental for determining not only the kind of machine we may operate, but also the quantitative bounds of its performance? Figuratively speaking, if the multiatom cluster is the "crude oil", the question is: Which preparation of the cluster is the refining process that can deliver a "gasoline" with a "specific octane"? We classify coherences or quantum correlations among the atoms according to their ability to serve as: (i) fuel for nonthermal machines corresponding to atomic states whose coherences displace or squeeze the cavity field, as well as cause its heating; and (ii) fuel that is purely "combustible", i.e., corresponds to atomic states that only allow for heat and entropy exchange with the field and can energize a proper heat engine. We identify highly promising multiatom states for each kind of fuel and propose viable experimental schemes for their implementation.

  • Improved charge separation and transport efficiency in panchromatic-sensitized solar cells with co-sensitization of PbS/CdS/ZnS quantum dots and dye molecules

    Luo S., Shen H., Hu W., Yao Z., Li J., Oron D., Wang N. & Lin H. (2016) RSC Advances.
    A panchromatic hybrid photoelectrode featuring co-sensitization of PbS quantum dots (QDs) and dye N719 with high charge separation efficiency was designed. In this photoelectrode, PbS QDs and N719 dye molecules exhibit a type-II energy level alignment, enabling efficient charge transfer between the two sensitizers and enhanced charge injection efficiency from sensitizers into TiO2, as confirmed by the significant PL quenching and time-resolved photoluminescence. Furthermore, we show the utility of a cobalt(II/III)-based redox electrolyte in solar cells based on PbS-N719 co-sensitized photoelectrodes, achieving a photovoltaic efficiency of over 2%. This result is comparable to the highest efficiencies obtained in cells of this type, and further verifies the important role of N719 as an intermediary agent in hole extraction from the PbS QDs. Compared to QD-only sensitized cells, co-sensitization significantly enhances the cell performance: the overall energy conversion efficiency by about 40% (from 1.55% to 2.12%) and the fill factor by about 20% (from 0.50 to 0.59). However, this system is still far from being optimal, and pathways towards its improvement are discussed.

  • Dynamics and Hydrodynamics of Molecular Superrotors

    Steinitz U., Khodorkovsky Y., Hartmann J. & Averbukh I. S. (2016) ChemPhysChem.
    In recent years, several femtosecond laser techniques have been developed that can make gas molecules rotate extremely fast, whereas the gas stays translationally cold. Herein we use molecular-dynamics simulations to investigate the collisional dynamics of gases of such molecules (superrotors). We found that the common route of superrotors to equilibrium is rather generic. It starts with a long-lasting gyroscopic stage, during which the molecules keep their fast rotation and the orientation of their angular momentum despite the many collisions they undergo. The inhibited rotational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, manifested in long-lasting optical birefringence and in anisotropic diffusion of the gas. Later, the gyroscopic stage is abruptly terminated by a self-accelerating explosive rotational-translational energy exchange that generates sound and macroscopic vortices with a hot rotating core.

  • Criticality of environmental information obtainable by dynamically controlled quantum probes

    Zwick A., Alvarez G. A. & Kurizki G. (2016) Physical Review A.
    A universal approach to decoherence control combined with quantum estimation theory reveals a critical behavior, akin to a phase transition, of the information obtainable by a qubit probe concerning the memory time of environmental fluctuations of generalized Ornstein-Uhlenbeck processes. The criticality is intrinsic to the environmental fluctuations but emerges only when the probe is subject to suitable dynamical control aimed at inferring the memory time. A sharp transition is anticipated between two dynamical phases characterized by either a short or long memory time compared to the probing time. This phase transition of the environmental information is a fundamental feature that characterizes open quantum-system dynamics and is important for attaining the highest estimation precision of the environment memory time under experimental limitations.

  • Widefield lensless imaging through a fiber bundle via speckle correlations

    Porat A., Andresen E. R., Rigneault H., Oron D., Gigan S. & Katz O. (2016) Optics Express.
    Flexible fiber-optic endoscopes provide a solution for imaging at depths beyond the reach of conventional microscopes. Current endoscopes require focusing and/or scanning mechanisms at the distal end, which limit miniaturization, frame-rate, and field of view. Alternative wavefront-shaping based lensless solutions are extremely sensitive to fiber-bending. We present a lensless, bend-insensitive, single-shot imaging approach based on speckle-correlations in fiber bundles that does not require wavefront shaping. Our approach computationally retrieves the target image by analyzing a single camera frame, exploiting phase information that is inherently preserved in propagation through convnetional fiber bundles. Unlike conventional fiber-based imaging, planar objects can be imaged at variable working distances, the resulting image is unpixelated and diffraction-limited, and miniaturization is limited only by the fiber diameter.

  • On the operation of machines powered by quantum non-thermal baths

    Niedenzu W., Gelbwaser-Klimovsky D., Kofman A. G. & Kurizki G. (2016) New Journal of Physics.
    Diverse models of engines energised by quantum-coherent, hence non-thermal, baths allow the engine efficiency to transgress the standard thermodynamic Carnot bound. These transgressions call for an elucidation of the underlying mechanisms. Here we show that non-thermal baths may impart not only heat, but also mechanical work to a machine. The Carnot bound is inapplicable to such a hybrid machine. Intriguingly, it may exhibit dual action, concurrently as engine and refrigerator, with up to 100% efficiency. We conclude that even though a machine powered by a quantum bath may exhibit an unconventional performance, it still abides by the traditional principles of thermodynamics.

  • Nonlinear quantum optics mediated by Rydberg interactions

    Firstenberg O., Adams C. S. & Hofferberth S. (2016) Journal of Physics B: Atomic, Molecular and Optical Physics.
    By mapping the strong interaction between Rydberg excitations in ultra-cold atomic ensembles onto single photons via electromagnetically induced transparency, it is now possible to realize a medium which exhibits a strong optical nonlinearity at the level of individual photons. We review the theoretical concepts and the experimental state-of-the-art of this exciting new field, and discuss first applications in the field of all-optical quantum information processing.

  • Attosecond processes and X-ray spectroscopy: General discussion

    Milne C. J., Weber P. M., Kowalewski M., Marangos J. P., Johnson A. S., Forbes R., Worner H. J., Rolles D., Townsend D., Schalk O., Mai S., Vacher M., Miller R. J. D., Centurion M., Vibok A., Domcke W., Cireasa R., Ueda K., Bencivenga F., Neumark D. M., Stolow A., Rudenko A., Kirrander A., Dowek D., Martin F., Ivanov M., Dahlstrom J. M., Dudovich N., Mukamel S., Sanchez-Gonzalez A., Minitti M. P., Austin D. R., Kimberg V. & Masin Z. (2016) Faraday Discussions.

  • Detailed Experimental Study of Ion Acceleration by Interaction of an Ultra-Short Intense Laser with an Underdense Plasma

    Kahaly S., Sylla F., Lifschitz A., Flacco A., Veltcheva M. & Malka V. (2016) Scientific Reports.
    Ion acceleration from intense (I lambda(2) > 1018 Wcm(-2) mu m(2)) laser-plasma interaction is experimentally studied within a wide range of He gas densities. Focusing an ultrashort pulse (duration. ion plasma period) on a newly designed submillimetric gas jet system, enabled us to inhibit total evacuation of electrons from the central propagation channel reducing the radial ion acceleration associated with ponderomotive Coulomb explosion, a mechanism predominant in the long pulse scenario. New ion acceleration mechanism have been unveiled in this regime leading to non-Maxwellian quasi monoenergetic features in the ion energy spectra. The emitted nonthermal ion bunches show a new scaling of the ion peak energy with plasma density. The scaling identified in this new regime differs from previously reported studies.

  • From dilute isovalent substitution to alloying in CdSeTe nanoplatelets

    Tenne R., Pedetti S., Kazes M., Ithurria S., Houben L., Nadal B., Oron D. & Dubertret B. (2016) Physical Chemistry Chemical Physics.
    Cadmium chalcogenide nanoplatelet (NPL) synthesis has recently witnessed a significant advance in the production of more elaborate structures such as core/shell and core/crown NPLs. However, controlled doping in these structures has proved difficult because of the restrictive synthetic conditions required for 2D anisotropic growth. Here, we explore the incorporation of tellurium (Te) within CdSe NPLs with Te concentrations ranging from doping to alloying. For Te concentrations higher than similar to 30%, the CdSexTe(1-x) NPLs show emission properties characteristic of an alloyed material with a bowing of the band gap for increased concentrations of Te. This behavior is in line with observations in bulk samples and can be put in the context of the transition from a pure material to an alloy. In the dilute doping regime, CdSe: Te NPLs, in comparison to CdSe NPLs, show a distinct photoluminescence (PL) red shift and prolonged emission lifetimes (LTs) associated with Te hole traps which are much deeper than in bulk samples. Furthermore, single particle spectroscopy reveals dramatic modifications in PL properties. In particular, doped NPLs exhibit photon antibunching and emission dynamics significantly modified compared to undoped or alloyed NPLs.

  • Facile: In situ synthesis of dendrite-like ZnO/ZnTe core/shell nanorod heterostructures for sensitized solar cells

    Luo S., Shen H., He X., Zhang Y., Li J., Oron D. & Lin H. (2016) Journal of Materials Chemistry C.
    ZnTe, a non-toxic low band gap semiconductor, has a direct band gap of 2.26 eV, and can be a promising candidate for non-toxic semiconductor sensitized solar cells (SSSCs). Herein, we report a simple and low-cost solution-processing approach to synthesize ZnTe nanocrystals by using dendrite-like ZnO nanorods as templates via an in situ method for application in solar cells. Structural and morphological analyses and systematic optical property investigations evidenced the successful synthesis of ZnTe nanocrystals and ZnO/ZnTe heterostructures. The measured band alignment of the heterostructures directly points to the strong effect of strain and the possibility to engineer the band offset at the ZnO/ZnTe interface. As ZnO and ZnTe exhibit a type-II energy level alignment, both significant absorption and efficient charge transfer are enabled between the two. Finally, solar cells based on the ZnO/ZnTe heterostructure were fabricated and a short-circuit photocurrent density of over 5 mA cm<sup>-2</sup> was achieved, benefiting from the preeminent absorption, high charge separation and transfer efficiency. A ZnS passivation layer dramatically improved the performance of the solar cells reaching a short-circuit photocurrent density of over 10 mA cm<sup>-2</sup>, along with an increase in the power conversion efficiency (PCE) from 0.46% to 1.7%. Potential pathways towards further increasing this figure are discussed.

  • Direct single-shot phase retrieval for separated objects (Conference Presentation)

    Leshem B., Xu R., Miao J., Nadler B., Oron D., Dudovich N. & Raz O. (2016) Quantitative Phase Imaging II.
    The phase retrieval problem arises in various fields ranging from physics and astronomy to biology and microscopy. Computational reconstruction of the Fourier phase from a single diffraction pattern is typically achieved using iterative alternating projections algorithms imposing a non-convex computational challenge. A different approach is holography, relying on a known reference field. Here we present a conceptually new approach for the reconstruction of two (or more) sufficiently separated objects. In our approach we combine the constraint the objects are finite as well as the information in the interference between them to construct an overdetermined set of linear equations. We show that this set of equations is guaranteed to yield the correct solution almost always and that it can be solved efficiently by standard numerical algebra tools. Essentially, our method combine commonly used constraint (that the object is finite) with a holographic approach (interference information). It differs from holographic methods in the fact that a known reference field is not required, instead the unknown objects serve as reference to one another (hence blind holography). Our method can be applied in a single-shot for two (or more) separated objects or with several measurements with a single object. It can benefit phase imaging techniques such as Fourier phytography microscopy, as well as coherent diffractive X-ray imaging in which the generation of a well-characterized, high resolution reference beam imposes a major challenge. We demonstrate our method experimentally both in the optical domain and in the X-ray domain using XFEL pulses.

  • Probing the Interaction of Quantum Dots with Chiral Capping Molecules Using Circular Dichroism Spectroscopy

    Ben-Moshe A., Teitelboim A., Oron D. & Markovich G. (2016) Nano Letters.
    Circular dichroism (CD) induced at exciton transitions by chiral ligands attached to single component and core/shell colloidal quantum dots (QDs) was used to study the interactions between QDs and their capping ligands. Analysis of the CD line shapes of CdSe and CdS QDs capped with l-cysteine reveals that all of the features in the complex spectra can be assigned to the different excitonic transitions. It is shown that each transition is accompanied by a derivative line shape in the CD response, indicating that the chiral ligand can split the exciton level into two new sublevels, with opposite angular momentum, even in the absence of an external magnetic field. The role of electrons and holes in this effect could be separated by experiments on various types of core/shell QDs, and it was concluded that the induced CD is likely related to interactions of the highest occupied molecular orbitals of the ligands with the holes. Hence, CD was useful for the analysis of hole level-ligand interactions in quantum semiconductor heterostructures, with promising outlook toward better general understanding the properties of the surface of such systems.

  • Controlled wake fields in interfering propagating surface plasmons

    Prior Y., Kaner R. & Sain B. (2016) .
    Plasmonic wakes are observed in a linear array of nanocavities in a gold film on glass substrate. The wakes are generated by the different propagation velocity of surface plasmons on the two sides of the film.

  • Colloidal Double Quantum Dots

    Teitelboim A., Meir N., Kazes M. & Oron D. (2016) Accounts of Chemical Research.
    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon emiss

  • Light-Induced Color Change in the Sapphirinid Copepods: Tunable Photonic Crystals

    Gur D., Leshem B., Farstey V., Oron D., Addadi L. & Weiner S. (2016) Advanced Functional Materials.
    Light-induced tunable photonic systems are rare in nature, and generally beyond the state-of-the-art in artificial systems. Sapphirinid male copepods produce some of the most spectacular colors in nature. The male coloration, used for communication purposes, is structural and is produced from ordered layers of guanine crystals separated by cytoplasm. It is generally accepted that the colors of the males are related to their location in the epipelagic zone. By combining correlative reflectance and cryoelectron microscopy image analyses, together with optical time lapse recording and transfer matrix modeling, it is shown that male sapphirinids have the remarkable ability to change their reflectance spectrum in response to changes in the light conditions. It is also shown that this color change is achieved by a change in the thickness of the cytoplasm layers that separate the guanine crystals. This change is reversible, and is both intensity and wavelength dependent. This capability provides the male with the ability to efficiently reflect light under certain conditions, while remaining transparent and hence camouflaged under other conditions. These copepods can thus provide inspiration for producing synthetic tunable photonic arrays.

  • Transformation Optics

    Leonhardt U. (2016) .
    According to Einstein’s general theory of relativity, the geometry of space-time is curved by the momentum and energy of macroscopic objects. This curvature is what we perceive as gravity, because it influences the motion of particles such as Newton’s apple falling from a tree in the space-time geometry curved by Earth or the planets circling around in the space-time geometry curved by the sun. Gravity also influences the propagation of waves, the most striking demonstration of which is gravitational lensing where light from distant stars or galaxies is deflected and focused in the space-time geometry created by other stars or galaxies. Gravity is universal, because the geometry of space and time sets the scene for everything, particle and wave alike.

  • Maximizing Information on the Environment by Dynamically Controlled Qubit Probes

    Zwick A., Alvarez G. & Kurizki G. (2016) Physical Review Applied.
    We explore the ability of a qubit probe to characterize unknown parameters of its environment. By resorting to the quantum estimation theory, we analytically find the ultimate bound on the precision of estimating key parameters of a broad class of ubiquitous environmental noises ("baths") which the qubit may probe. These include the probe-bath coupling strength, the correlation time of generic types of bath spectra, and the power laws governing these spectra, as well as their dephasing times T2. Our central result is that by optimizing the dynamical control on the probe under realistic constraints one may attain the maximal accuracy bound on the estimation of these parameters by the least number of measurements possible. Applications of this protocol that combines dynamical control and estimation theory tools to quantum sensing are illustrated for a nitrogen-vacancy center in diamond used as a probe.

  • From Coherent to Incoherent Dynamical Control of Open Quantum Systems

    Kurizki G. & Zwick A. (2016) .
    Coherence control was originally conceived by Shapiro and Brumer for closed quantum systems. In open quantum systems, the environment hampers or destroys coherence. Nevertheless, the Kurizki-Shapiro-Brumer coherent photocurrent control showed partial resilience to decoherence. Still, decoherence control is an essential prerequisite to our ability to fully exploit quantum coherence for any operational task. Yet decoherence control need not employ coherent fields: it may be incoherent. In operational tasks such as the preparation, transformation, transmission, and detection of quantumstates, environmental (bath) effects can be suppressed by dynamical decoupling, or by the more general incoherent dynamical control by modulation developed by our group. The resulting control dynamics must be Zeno-like in order to yield suppressed coupling to the bath in unitary operational tasks. There are however tasks which cannot be implemented by closed-system (unitary) evolution, in particular those involving a change of the system's entropy. Such tasks necessitate efficient coupling to a bath for their implementation. Examples are the use of measurements to cool (purify) a system, to equilibrate it, or harvest (and convert) energy from the environment. If the underlying dynamics is anti-Zeno like, enhancement of this coupling to the bath will occur and thereby facilitate the task, as discovered by us. A general task may also require state and energy transfer between non-interacting parties via shared modes of the bath. For such tasks, a more subtle interplay of Zeno and anti-Zeno dynamics may be optimal. We have therefore constructed a general framework for optimizing the way a system interacts with its environment to achieve a desired task. This optimization consists in adjusting a given "score" that quantifies the success of the task, such as the targeted fidelity, purity, entropy, energy or state transfer probability by dynamical modification of the system-bath coupling spectrum on demand.

  • Energy boost in laser wakefield accelerators using sharp density transitions

    Dopp A., Guillaume E., Thaury C., Lifschitz A., Phuoc K. T. & Malka V. (2016) Physics of Plasmas.
    The energy gain in laser wakefield accelerators is limited by dephasing between the driving laser pulse and the highly relativistic electrons in its wake. Since this phase depends on both the driver and the cavity length, the effects of dephasing can be mitigated with appropriate tailoring of the plasma density along propagation. Preceding studies have discussed the prospects of continuous phase-locking in the linear wakefield regime. However, most experiments are performed in the highly non-linear regime and rely on self-guiding of the laser pulse. Due to the complexity of the driver evolution in this regime, it is much more difficult to achieve phase locking. As an alternative, we study the scenario of rapid rephasing in sharp density transitions, as was recently demonstrated experimentally. Starting from a phenomenological model, we deduce expressions for the electron energy gain in such density profiles. The results are in accordance with particle-in-cell simulations, and we present gain estimations for single and multiple stages of rephasing. Published by AIP Publishing.

  • Three-dimensional metamaterials for nonlinear holography

    Prior Y., Bitton O. & Almeida E. (2016) .
    We demonstrate full control of the nonlinear phase in 3D, multilayer metamaterials. Functional nonlinear optical elements are designed and fabricated, demonstrating capabilities to generate and shape light beams and computer generated nonlinear holography.

  • Probe of Multielectron Dynamics in Xenon by Caustics in High-Order Harmonic Generation

    Facciala D., Pabst S., Bruner B., Ciriolo A., De Silvestri S. S., Devetta M., Negro M., Soifer H., Stagira S., Dudovich N. & Vozzi C. (2016) Physical review letters.
    We investigated the giant resonance in xenon by high-order harmonic generation spectroscopy driven by a two-color field. The addition of a nonperturbative second harmonic component parallel to the driving field breaks the symmetry between neighboring subcycles resulting in the appearance of spectral caustics at two distinct cutoff energies. By controlling the phase delay between the two color components it is possible to tailor the harmonic emission in order to amplify and isolate the spectral feature of interest. In this Letter we demonstrate how this control scheme can be used to investigate the role of electron correlations that give birth to the giant resonance in xenon. The collective excitations of the giant dipole resonance in xenon combined with the spectral manipulation associated with the two-color driving field allow us to see features that are normally not accessible and to obtain a good agreement between the experimental results and the theoretical predictions.

  • Manipulating relativistic electrons with lasers

    Malka V. (2016) EPL.
    The motion control of relativistic electrons with lasers allows for an efficient and elegant way to map the space with ultra-intense electric-field components, which, in turn, permits a unique improvement of the electron beam parameters. This perspective addresses the recent laser plasma accelerator experiments related to the phase space engineering of electron beams in a plasma medium performed at LOA.

  • Echoes in space and time

    Lin K., Lu P., Ma J., Gong X., Song Q., Ji Q., Zhang W., Zeng H., Wu J., Karras G., Siour G., Hartmann J., Faucher O., Gershnabel E., Prior Y. & Averbukh I. S. (2016) Physical Review X.
    Echo in mountains is a well-known phenomenon, where an acoustic pulse is mirrored by the rocks, often with reverberating recurrences. For spin echoes in magnetic resonance and photon echoes in atomic and molecular systems, the role of the mirror is played by a second, time-delayed pulse that is able to reverse the flow of time and recreate the original impulsive event. Recently, alignment and orientation echoes were discussed in terms of rotational-phase-space filamentation, and they were optically observed in laserexcited molecular gases. Here, we observe hitherto unreported fractional echoes of high order, spatially rotated echoes, and the counterintuitive imaginary echoes at negative times. Coincidence Coulomb explosion imaging is used for a direct spatiotemporal analysis of various molecular alignment echoes, and the implications to echo phenomena in other fields of physics are discussed.

  • Experimental observation of fractional echoes

    Karras G., Hertz E., Billard F., Lavorel B., Siour G., Hartmann J. -., Faucher O., Gershnabel E., Prior Y. & Averbukh I. S. (2016) Physical Review A.
    We report the observation of fractional echoes in a double-pulse excited nonlinear system. Unlike standard echoes, which appear periodically at delays which are integer multiples of the delay between the two exciting pulses, the fractional echoes appear at rational fractions of this delay. We discuss the mechanism leading to this phenomenon, and provide experimental demonstration of fractional echoes by measuring third harmonic generation in a thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses.

  • Deterministic photon-atom and photon-photon interactions based on single-photon Raman interaction

    Bechler O., Rosenblum S., Shomroni I., Lovsky Y., Guendelman G. & Dayan B. (2016) Proceedings of SPIE - The International Society for Optical Engineering.
    We demonstrate a passive scheme for deterministic interactions between a single photon and a single atom. Relying on single-photon Raman interaction (SPRINT), this control-fields free scheme swaps a flying qubit, encoded in the two possible input modes of a photon, with a stationary qubit, encoded in the two ground states of the atom, and can be also harnessed to perform universal quantum gates. Using SPRINT we experimentally demonstrated all-optical switching of single photons by single photons, and deterministic extraction of a single photon from an optical pulse. Applicable to any atom-like Lambda system, SPRINT provides a versatile building block for scalable quantum networks based on completely passive nodes interconnected and activated solely by single photons.

  • Hawking spectrum for a fiber-optical analog of the event horizon

    Bermudez D. & Leonhardt U. (2016) Physical Review A.
    Hawking radiation has been regarded as a more general phenomenon than in gravitational physics, in particular in laboratory analogs of the event horizon. Here we consider the fiber-optical analog of the event horizon, where intense light pulses in fibers establish horizons for probe light. Then, we calculate the Hawking spectrum in an experimentally realizable system. We found that the Hawking radiation is peaked around group-velocity horizons in which the speed of the pulse matches the group velocity of the probe light. The radiation nearly vanishes at the phase horizon where the speed of the pulse matches the phase velocity of light.

  • Extended field-of-view in a lensless endoscope using an aperiodic multicore fiber

    Sivankutty S., Tsvirkun V., Bouwmans G., Kogan D., Oron D., Andresen E. R. & Rigneault H. (2016) Optics Letters.
    We investigate lensless endoscopy using coherent beam combining and aperiodic multicore fibers (MCF). We show that diffracted orders, inherent to MCF with periodically arranged cores, dramatically reduce the field-of-view (FoV), and that randomness in MCF core positions can increase the FoV up to the diffraction limit set by a single fiber core, while maintaining a MCF experimental feasibility. We demonstrate experimentally pixelation-free lensless endoscopy imaging over a 120 μm FoV with an aperiodic MCF designed with widely spaced cores. We show that this system is suitable to perform beam scanning imaging by simply applying a tilt to the proximal wavefront.

  • Single spin magnetic resonance

    Wrachtrup J. & Finkler A. (2016) Journal of Magnetic Resonance.
    Different approaches have improved the sensitivity of either electron or nuclear magnetic resonance to the single spin level. For optical detection it has essentially become routine to observe a single electron spin or nuclear spin. Typically, the systems in use are carefully designed to allow for single spin detection and manipulation, and of those systems, diamond spin defects rank very high, being so robust that they can be addressed, read out and coherently controlled even under ambient conditions and in a versatile set of nanostructures. This renders them as a new type of sensor, which has been shown to detect single electron and nuclear spins among other quantities like force, pressure and temperature. Adapting pulse sequences from classic NMR and EPR, and combined with high resolution optical microscopy, proximity to the target sample and nanoscale size, the diamond sensors have the potential to constitute a new class of magnetic resonance detectors with single spin sensitivity. As diamond sensors can be operated under ambient conditions, they offer potential application across a multitude of disciplines. Here we review the different existing techniques for magnetic resonance, with a focus on diamond defect spin sensors, showing their potential as versatile sensors for ultra-sensitive magnetic resonance with nanoscale spatial resolution.

  • Summary of working group 1: Electron beam from plasmas

    Malka V. & Gschwendtner E. (2016) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment.
    We briefly summarize the contributions that have been presented in the 5 working group 1 (WG1) sessions dedicated to electron beam from plasmas. 

  • Revisiting the Anion Framework Conservation in Cation Exchange Processes

    Meir N., Martin-Garcia B., Moreels I. & Oron D. (2016) Chemistry of Materials.
    We investigated the effect of cation exchange on the anionic framework of lightly doped CdSe:Te/CdS nanorods. In contrast with previously studied core/shell systems, the Te dopant, located in the center of the CdSe core, provides an extremely sensitive indicator for any structural changes of the anionic framework that may occur as a result of the cation exchange process. We first optimized the cation exchange procedure in order to retain the fluorescence properties of the CdSe:Te/CdS nanorods after exchange of Cd2+ for Cu+ and back to Cd2+. Next, using multiexciton spectroscopy, we were able to probe the magnitude of the exciton exciton repulsion interaction and use that to assess the degree of crystal structure conservation. Our findings provide a much stronger proof that the anion framework is indeed rigid, showing no evidence of significant migration of the anionic dopant.

  • Efficient laser production of energetic neutral beams

    Mollica F., Antonelli L., Flacco A., Braenzel J., Vauzour B., Folpini G., Birindelli G., Schnuerer M., Batani D. & Malka V. (2016) Plasma Physics and Controlled Fusion.
    Laser-driven ion acceleration by intense, ultra-short, laser pulse has received increasing attention in recent years, and the availability of much compact and versatile ions sources motivates the study of laser-driven sources of energetic neutral atoms. We demonstrate the production of a neutral and directional beam of hydrogen and carbon atoms up to 200 keV per nucleon, with a peak flow of 2.7 x 10(13) atom s(-1). Laser accelerated ions are neutralized in a pulsed, supersonic argon jet with tunable density between 1.5 x 10(17) cm(-3) and 6 x 10(18) cm(-3). The neutralization efficiency has been measured by a time-of-flight detector for different argon densities. An optimum is found, for which complete neutralization occurs. The neutralization rate can be explained only at high areal densities (> 1 x 10(17) cm(-2)) by single electron charge transfer processes. These results suggest a new perspective for the study of neutral production by laser and open discussion of neutralization at a lower density.

  • Subwavelength nonlinear phase control and anomalous phase matching in plasmonic metasurfaces

    Almeida E., Shalem G. & Prior Y. (2016) Nature Communications.
    Metasurfaces, and in particular those containing plasmonic-based metallic elements, constitute an attractive set of materials with a potential for replacing standard bulky optical elements. In recent years, increasing attention has been focused on their nonlinear optical properties, particularly in the context of second and third harmonic generation and beam steering by phase gratings. Here, we harness the full phase control enabled by subwavelength plasmonic elements to demonstrate a unique metasurface phase matching that is required for efficient nonlinear processes. We discuss the difference between scattering by a grating and by subwavelength phase-gradient elements. We show that for such interfaces an anomalous phase-matching condition prevails, which is the nonlinear analogue of the generalized Snell's law. The subwavelength phase control of optical nonlinearities paves the way for the design of ultrathin, flat nonlinear optical elements. We demonstrate nonlinear metasurface lenses, which act both as generators and as manipulators of the frequency-converted signal.

  • Rotational Doppler effect in harmonic generation from spinning molecules

    Faucher O., Prost E., Hertz E., Billard F., Lavorel B., Milner A. A., Milner V. A., Zyss J. & Averbukh I. S. (2016) Physical Review A.
    We present an observation of the rotational Doppler shift in the frequency of optical harmonic generated in fast rotating molecules. Conservation of energy and angular momentum in the light-molecule interaction suggests four different kinds of shifts depending on the mutual handedness of the circularly polarized fundamental and harmonic fields, as well as the handedness of the molecular rotation. All four types of the frequency shifts were observed in our experiments on third-harmonic generation in a gas of fast spinning O-2 molecules.

  • Dynamics of a Ground-State Cooled Ion Colliding with Ultracold Atoms

    Meir Z., Sikorsky T., Ben Shlomi R., Akerman N., Dallal Y. & Ozeri R. (2016) Physical review letters.
    Ultracold atom-ion mixtures are gaining increasing interest due to their potential applications in ultracold and state-controlled chemistry, quantum computing, and many-body physics. Here, we studied the dynamics of a single ground-state cooled ion during few, to many, Langevin (spiraling) collisions with ultracold atoms. We measured the ion's energy distribution and observed a clear deviation from the Maxwell-Boltzmann distribution, characterized by an exponential tail, to a power-law distribution best described by a Tsallis function. Unlike previous experiments, the energy scale of atom-ion interactions is not determined by either the atomic cloud temperature or the ion's trap residual excess-micromotion energy. Instead, it is determined by the force the atom exerts on the ion during a collision which is then amplified by the trap dynamics. This effect is intrinsic to ion Paul traps and sets the lower bound of atomion steady-state interaction energy in these systems. Despite the fact that our system is eventually driven out of the ultracold regime, we are capable of studying quantum effects by limiting the interaction to the first collision when the ion is initialized in the ground state of the trap.

  • An application of laser-plasma acceleration: towards a free-electron laser amplification

    Couprie M. E., Labat M., Evain C., Marteau F., Briquez F., Khojoyan M., Benabderrahmane C., Chapuis L., Hubert N., Bourassin-Bouchet C., El Ajjouri M., Bouvet F., Dietrich Y., Valleau M., Sharma G., Yang W., Marcouille O., Veteran J., Berteaud P., El Ajjouri T., Cassinari L., Thaury C., Lambert G., Andriyash I., Malka V., Davoine X., Tordeux M. A., Miron C., Zerbib D., Tavakoli K., Marlats J. L., Tilmont M., Rommeluere P., Duval J. P., N'Guyen M. H., Rouqier A., Vanderbergue M., Herbeaux C., Sebdouai M., Lestrade A., Leclercq N., Dennetiere D., Thomasset M., Polack F., Bielawski S., Szwaj C. & Loulergue A. (2016) Plasma Physics and Controlled Fusion.
    The laser-plasma accelerator (LPA) presently provides electron beams with a typical current of a few kA, a bunch length of a few fs, energy in the few hundred MeV to several GeV range, a divergence of typically 1 mrad, an energy spread of the order of 1%, and a normalized emittance of the order of pi.mm. mrad. One of the first applications could be to use these beams for the production of radiation: undulator emission has been observed but the rather large energy spread (1%) and divergence (1 mrad) prevent straightforward free-electron laser (FEL) amplification. An adequate beam manipulation through the transport to the undulator is then required. The key concept proposed here relies on an innovative electron beam longitudinal and transverse manipulation in the transport towards an undulator: a 'demixing' chicane sorts the electrons according to their energy and reduces the spread from 1% to one slice of a few parts per thousand and the effective transverse size is maintained constant along the undulator (supermatching) by a proper synchronization of the electron beam focusing with the progress of the optical wave. A test experiment for the demonstration of FEL amplification with an LPA is under preparation. Electron beam transport follows different steps with strong focusing with permanent magnet quadrupoles of variable strength, a demixing chicane with conventional dipoles, and a second set of quadrupoles for further focusing in the undulator. The FEL simulations and the progress of the preparation of the experiment are presented.

  • Quantum Dynamics in Phase Space using Projected von Neumann Bases

    Machnes S., Assemat E., Larsson H. R. & Tannor D. (2016) Journal of Physical Chemistry A.
    We describe the mathematical underpinnings of the biorthogonal von Neumann method for quantum mechanical simulations (PvB). In particular, we present a detailed discussion of the important issue of nonorthogonal projection onto subspaces of biorthogonal bases, and how this differs from orthogonal projection. We present various representations of the Schrödinger equation in the reduced basis and discuss their relative merits. We conclude with illustrative examples and a discussion of the outlook and challenges ahead for the PvB representation.

  • Nonlinear metamaterials for holography

    Almeida E., Bitton O. & Prior Y. (2016) Nature Communications.
    A hologram is an optical element storing phase and possibly amplitude information enabling the reconstruction of a three-dimensional image of an object by illumination and scattering of a coherent beam of light, and the image is generated at the same wavelength as the input laser beam. In recent years, it was shown that information can be stored in nanometric antennas giving rise to ultrathin components. Here we demonstrate nonlinear multilayer metamaterial holograms. A background free image is formed at a new frequency - the third harmonic of the illuminating beam. Using e-beam lithography of multilayer plasmonic nanoantennas, we fabricate polarization-sensitive nonlinear elements such as blazed gratings, lenses and other computer-generated holograms. These holograms are analysed and prospects for future device applications are discussed.

  • Dialogues about geometry and light

    Bermudez D., Drori J. & Leonhardt U. (2016) .
    Throughout human history, people have used sight to learn about the world, but only in relatively recent times the science of light has been developed. Egyptians and Mesopotamians made the first known lenses out of quartz, giving birth to what was later known as optics. On the other hand, geometry is a branch of mathematics that was born from practical studies concerning lengths, areas and volumes in the early cultures, although it was not put into axiomatic form until the 3rd century BC. In this work, we will discuss the connection between these two timeless topics and show some "new things in old things". There have been several works in this direction, but taking into account the didactic approach of the "Enrico Fermi" Summer School, we would like to address the subject and our audience in a new light.

  • A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator

    Doepp A., Guillaume E., Thaury C., Lifschitz A., Sylla F., Goddet J., Tafzi A., Iaquanello G., Lefrou T., Rousseau P., Conejero E., Ruiz C., Phuoc K. T. & Malka V. (2016) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment.
    Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge scales approximately with the laser energy and is limited by beam loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per shot, originating mostly from electrons of less than 10 MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1 Hz repetition rate. In accordance with GEANT4 Monte-Carlo simulations, we measure a gamma-ray source size of less than 100 mu m for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators.

  • Two-Dimensional Frequency Resolved Optomolecular Gating of High-Order Harmonic Generation

    Ferre A., Soifer H., Pedatzur O., Bourassin-Bouchet C., Bruner B., Canonge R., Catoire F., Descamps D., Fabre B., Mevel E., Petit S., Dudovich N. & Mairesse Y. (2016) Physical review letters.
    Probing electronic wave functions of polyatomic molecules is one of the major challenges in high-harmonic spectroscopy. The extremely nonlinear nature of the laser-molecule interaction couples the multiple degrees of freedom of the probed system. We combine two-dimensional control of the electron trajectories and vibrational control of the molecules to disentangle the two main steps in high-harmonic generation - ionization and recombination. We introduce a new measurement scheme, frequency-resolved optomolecular gating, which resolves the temporal amplitude and phase of the harmonic emission from excited molecules. Focusing on the study of vibrational motion in N2O4, we show that such advanced schemes provide a unique insight into the structural and dynamical properties of the underlying mechanism.

  • Non-Signaling Parallel Repetition Using de Finetti Reductions

    Arnon-Friedman R., Renner R. & Vidick T. (2016) IEEE Transactions on Information Theory.
    In the context of multiplayer games, the parallel repetition problem can be phrased as follows: given a game G with optimal winning probability 1 - α and its repeated version G n (in which n games are played together, in parallel), can the players use strategies that are substantially better than ones in which each game is played independently? This question is relevant in physics for the study of correlations and plays an important role in computer science in the context of complexity and cryptography. In this paper, the case of multiplayer non-signaling games is considered, i.e., the only restriction on the players is that they are not allowed to communicate during the game. For complete-support games (games where all possible combinations of questions have non-zero probability to be asked) with any number of players, we prove a threshold theorem stating that the probability that non-signaling players win more than a fraction 1-α+β of the n games is exponentially small in nβ 2 for every 0 ≤ β ≤ α. For games with incomplete support, we derive a similar statement for a slightly modified form of repetition. The result is proved using a new technique based on a recent de Finetti theorem, which allows us to avoid central technical difficulties that arise in standard proofs of parallel repetition theorems.

  • Speed and efficiency limits of multilevel incoherent heat engines

    Mukherjee V., Niedenzu W., Kofman A. G. & Kurizki G. (2016) Physical Review E.
    We present a comprehensive theory of heat engines (HE) based on a quantum-mechanical "working fluid" (WF) with periodically modulated energy levels. The theory is valid for any periodicity of driving Hamiltonians that commute with themselves at all times and do not induce coherence in the WF. Continuous and stroke cycles arise in opposite limits of this theory, which encompasses hitherto unfamiliar cycle forms, dubbed here hybrid cycles. The theory allows us to discover the speed, power, and efficiency limits attainable by incoherently operating multilevel HE depending on the cycle form and the dynamical regimes.

  • Extraction of a single photon from an optical pulse

    Rosenblum S., Bechler O., Shomroni I., Lovsky Y., Guendelman G. & Dayan B. (2016) Nature Photonics.
    Removing a single photon from a pulse is one of the most elementary operations that can be performed on light, having both fundamental significance and practical applications in quantum communication and computation. So far, photon subtraction, in which the removed photon is detected and therefore irreversibly lost, has been implemented in a probabilistic manner with inherently low success rates using low-reflectivity beam splitters. Here we demonstrate a scheme for the deterministic extraction of a single photon from an incoming pulse. The removed photon is diverted to a different mode, enabling its use for other purposes, such as a photon number-splitting attack on quantum key distribution protocols. Our implementation makes use of single-photon Raman interaction (SPRINT) with a single atom near a nanofibre-coupled microresonator. The single-photon extraction probability in our current realization is limited mostly by linear loss, yet probabilities close to unity should be attainable with realistic experimental parameters.

  • An all-optical Compton source for single-exposure x-ray imaging

    Dopp A., Guillaume E., Thaury C., Gautier J., Andriyash I., Lifschitz A., Malka V., Rousse A. & Phuoc K. T. (2016) Plasma Physics and Controlled Fusion.
    All-optical Compton sources are innovative, compact devices to produce high energy femtosecond x-rays. Here we present results on a single-pulse scheme that uses a plasma mirror to reflect the drive beam of a laser plasma accelerator and to make it collide with the highly-relativistic electrons in its wake. The accelerator is operated in the self-injection regime, producing quasi-monoenergetic electron beams of around 150 MeV peak energy. Scattering with the intense femtosecond laser pulse leads to the emission of a collimated high energy photon beam. Using continuum-attenuation filters we measure significant signal content beyond 100 keV and with simulations we estimate a peak photon energy of around 500 keV. The source divergence is about 13 mrad and the pointing stability is 7 mrad. We demonstrate that the photon yield from the source is sufficiently high to illuminate a centimeter-size sample placed 90 centimeters behind the source, thus obtaining radiographs in a single shot.

  • Three-Dimensional Holographic Nonlinear Metamaterials

    Almeida E. & Prior Y. (2016) .
    We demonstrate full control of the nonlinear phase in 3D, multilayer metamaterials. Functional nonlinear optical elements are designed and fabricated, demonstrating capabilities to generate and shape light beams and computer generated nonlinear holography.

  • Multidimensional high harmonic spectroscopy of polyatomic molecules: Detecting sub-cycle laser-driven hole dynamics upon ionization in strong mid-IR laser fields

    Bruner B. D., Masin Z., Negro M., Morales F., Brambila D., Devetta M., Facciala D., Harvey A. G., Ivanov M., Mairesse Y., Patchkovskii S., Serbinenko V., Soifer H., Stagira S., Vozzi C., Dudovich N. & Smirnova O. (2016) Faraday Discussions.
    High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales. We detect the signatures of laser-driven hole dynamics upon ionization and reconstruct the relative phases and amplitudes for relevant ionization channels in a CO<sub>2</sub> molecule on a sub-cycle time scale. Reconstruction of channel-resolved complex ionization amplitudes on attosecond time scales has been a long-standing goal of high harmonic spectroscopy. Our study brings us one step closer to fulfilling this initial promise and developing robust schemes for sub-femtosecond imaging of multielectron rearrangement in complex molecular systems.

  • Direct single-shot phase retrieval from thediffraction pattern of separated objects

    Leshem B., Xu R., Dallal Y., Miao J., Nadler B., Oron D., Dudovich N. & Raz O. (2016) Nature Communications.
    The non-crystallographic phase problem arises in numerous scientific and technological fields. An important application is coherent diffractive imaging. Recent advances in X-ray free-electron lasers allow capturing of the diffraction pattern from a single nanoparticle before it disintegrates, in so-called â € diffraction before destructionâ € experiments. Presently, the phase is reconstructed by iterative algorithms, imposing a non-convex computational challenge, or by Fourier holography, requiring a well-characterized reference field. Here we present a convex scheme for single-shot phase retrieval for two (or more) sufficiently separated objects, demonstrated in two dimensions. In our approach, the objects serve as unknown references to one another, reducing the phase problem to a solvable set of linear equations. We establish our method numerically and experimentally in the optical domain and demonstrate a proof-of-principle single-shot coherent diffractive imaging using X-ray free-electron lasers pulses. Our scheme alleviates several limitations of current methods, offering a new pathway towards direct reconstruction of complex objects.

  • Highly nonlocal optical nonlinearities in atoms trapped near a waveguide

    Shahmoon E., Grisins P., Stimming H. P., Mazets I. & Kurizki G. (2016) Optica.
    Nonlinear optical phenomena are typically local. Here, we predict the possibility of highly nonlocal optical nonlinearities for light propagating in atomic media trapped near a nano-waveguide, where long-range interactions between the atoms can be tailored. When the atoms are in an electromagnetically induced transparency configuration, the atomic interactions are translated to long-range interactions between photons and thus to highly nonlocal optical nonlinearities. We derive and analyze the governing nonlinear propagation equation, finding a roton-like excitation spectrum for light and the emergence of order in its output intensity. These predictions open the door to studies of unexplored wave dynamics and many-body physics with highly nonlocal interactions of optical fields in one dimension. (C) 2016 Optical Society of America

  • Characterization of the ELIMED Permanent Magnets Quadrupole system prototype with laser-driven proton beams

    Schillaci F., Pommarel L., Romano F., Cuttone G., Costa M., Giove D., Maggiore M., Russo A. D., Scuderi V., Malka V., Vauzour B., Flacco A. & Cirrone G. A. P. (2016) Journal of Instrumentation.
    Laser-based accelerators are gaining interest in recent years as an alternative to conventional machines [1]. In the actual ion acceleration scheme, energy and angular spread of the laser-driven beams are the main limiting factors for beam applications and different solutions for dedicated beam-transport lines have been proposed [2, 3]. In this context a system of Permanent Magnet Quadrupoles (PMQs) has been realized [4] by INFN-LNS (Laboratori Nazionali del Sud of the Instituto Nazionale di Fisica Nucleare) researchers, in collaboration with SIGMAPHI company in France, to be used as a collection and pre-selection system for laser driven proton beams. This system is meant to be a prototype to a more performing one [5] to be installed at ELI-Beamlines for the collection of ions. The final system is designed for protons and carbons up to 60 MeV/u. In order to validate the design and the performances of this large bore, compact, high gradient magnetic system prototype an experimental campaign have been carried out, in collaboration with the group of the SAPHIR experimental facility at LOA (Laboratoire d'Optique Appliquee) in Paris using a 200 TW Ti:Sapphire laser system. During this campaign a deep study of the quadrupole system optics has been performed, comparing the results with the simulation codes used to determine the setup of the PMQ system and to track protons with realistic TNSA-like divergence and spectrum. Experimental and simulation results are good agreement, demonstrating the possibility to have a good control on the magnet optics. The procedure used during the experimental campaign and the most relevant results are reported here.

  • Inhibition of charge transfer and recombination processes in CdS/N719 co-sensitized solar cell with high conversion efficiency

    Luo S., Shen H., Zhang Y., Li J., Oron D. & Lin H. (2016) Electrochimica Acta.
    In the hybrid structure employing CdS/N719 QD/dye co-sensitized photoelectrode, it is revealed by consistent results from the steady-state and time-resolved photoluminescence (PL) that the QD regeneration was realized by the effective charge transfer from the dye sensitizer, resulting in a significant PL quenching. This is helpful for retarding the recombination in the device. Furthermore, by varying the thickness of the TiO<sub>2</sub> film, the light harvesting efficiency and the charge collection efficiency were balanced, leading to an optimal TiO<sub>2</sub> thickness of 22 μm and a power conversion efficiency (PCE) of about 6.5%. Compared with the dye N719 only sensitized system with the same dye loading(with an efficiency of 5.09%), the co-sensitization of dye N719 and CdS (with an efficiency of 6.44%) enhanced the overall PCE significantly by 26.5% Notably, this is one of the best reported efficiencies for the QD-dye co-sensitized solar cells.

  • Quantum-proof multi-source randomness extractors in the Markov model

    Arnon-Friedman R., Portmann C. & Scholz V. B. (2016) .
    Randomness extractors, widely used in classical and quantum cryptography and other fields of computer science, e.g., derandomization, are functions which generate almost uniform randomness from weak sources of randomness. In the quantum setting one must take into account the quantum side information held by an adversary which might be used to break the security of the extractor. In the case of seeded extractors the presence of quantum side information has been extensively studied. For multi-source extractors one can easily see that high conditional min-entropy is not sufficient to guarantee security against arbitrary side information, even in the classical case. Hence, the interesting question is under which models of (both quantum and classical) side information multi-source extractors remain secure. In this work we suggest a natural model of side information, which we call the Markov model, and prove that any multi-source extractor remains secure in the presence of quantum side information of this type (albeit with weaker parameters). This improves on previous results in which more restricted models were considered or the security of only some types of extractors was shown.

  • Broadband near-infrared to visible upconversion in quantum dot-quantum well heterostructures

    Teitelboim A. & Oron D. (2016) ACS Nano.
    Upconversion is a nonlinear process in which two, or more, long wavelength photons are converted to a shorter wavelength photon. It holds great promise for bioimaging, enabling spatially resolved imaging in a scattering specimen and for photovoltaic devices as a means to surpass the Shockley-Queisser efficiency limit. Here, we present dual near-infrared and visible emitting PbSe/CdSe/CdS nanocrystals able to upconvert a broad range of NIR wavelengths to visible emission at room temperature. The synthesis is a three-step process, which enables versatility and tunability of both the visible emission color and the NIR absorption edge. Using this method, one can achieve a range of desired upconverted emission peak positions with a suitable NIR band gap.

  • Special issue on coherence and control in the quantum world

    Averbukh I., Hepburn J., Milner V. & Tannor D. (2016) Journal of Physics B: Atomic, Molecular and Optical Physics.

  • Structural Attributes and Photodynamics of Visible Spectrum Quantum Emitters in Hexagonal Boron Nitride

    Chejanovsky N., Rezai M., Paolucci F., Kim Y., Rendler T., Rouabeh W., de Oliveira F. F., Herlinger P., Denisenko A., Yang S., Gerhardt I., Finkler A., Smet J. H. & Wrachtrup J. (2016) Nano Letters.
    Newly discovered van der Waals materials like MoS<sub>2</sub>, WSe<sub>2</sub>, hexagonal boron nitride (h-BN), and recently C<sub>2</sub>N have sparked intensive research to unveil the quantum behavior associated with their 2D structure. Of great interest are 2D materials that host single quantum emitters. h-BN, with a band gap of 5.95 eV, has been shown to host single quantum emitters which are stable at room temperature in the UV and visible spectral range. In this paper we investigate correlations between h-BN structural features and emitter location from bulk down to the monolayer at room temperature. We demonstrate that chemical etching and ion irradiation can generate emitters in h-BN. We analyze the emitters' spectral features and show that they are dominated by the interaction of their electronic transition with a single Raman active mode of h-BN. Photodynamics analysis reveals diverse rates between the electronic states of the emitter. The emitters show excellent photo stability even under ambient conditions and in monolayers. Comparing the excitation polarization between different emitters unveils a connection between defect orientation and the h-BN hexagonal structure. The sharp spectral features, color diversity, room-temperature stability, long-lived metastable states, ease of fabrication, proximity of the emitters to the environment, outstanding chemical stability, and biocompatibility of h-BN provide a completely new class of systems that can be used for sensing and quantum photonics applications.

  • Nonlinear optics: Resolving the attosecond beat

    Krüger M. & Dudovich N. (2016) Nature Photonics.

  • Theory of Maxwell's fish eye with mutually interacting sources and drains

    Leonhardt U. & Sahebdivan S. (2015) Physical Review A.
    Maxwell's fish eye is predicted to image with a resolution not limited by the wavelength of light. However, interactions between sources and drains may ruin the subwavelength imaging capabilities of this and similar absolute optical instruments. Nevertheless, as we show in this paper, at resonance frequencies of the device, an array of drains may resolve a single source, or alternatively, a single drain may scan an array of sources, no matter how narrowly spaced they are. It seems that near-field information can be obtained from far-field distances.

  • Multidimensional high harmonic spectroscopy

    Bruner B. D., Soifer H., Shafir D., Serbinenko V., Smirnova O. & Dudovich N. (2015) JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS.
    High harmonic generation (HHG) has opened up a new frontier in ultrafast science where attosecond time resolution and Angstrom spatial resolution are accessible in a single measurement. However, reconstructing the dynamics under study is limited by the multiple degrees of freedom involved in strong field interactions. In this paper we describe a new class of measurement schemes for resolving attosecond dynamics, integrating perturbative nonlinear optics with strong-field physics. These approaches serve as a basis for multidimensional high harmonic spectroscopy. Specifically, we show that multidimensional high harmonic spectroscopy can measure tunnel ionization dynamics with high precision, and resolves the interference between multiple ionization channels. In addition, we show how multidimensional HHG can function as a type of lock-in amplifier measurement. Similar to multi-dimensional approaches in nonlinear optical spectroscopy that have resolved correlated femtosecond dynamics, multi-dimensional high harmonic spectroscopy reveals the underlying complex dynamics behind attosecond scale phenomena.

  • Universal gate-set for trapped-ion qubits using a narrow linewidth diode laser

    Akerman N., Navon N., Kotler S., Glickman Y. & Ozeri R. (2015) New Journal of Physics.
    We report on the implementation of a high fidelity universal gate-set on optical qubits based on trapped <sup>88</sup>Sr<sup>+</sup> ions for the purpose of quantum information processing. All coherent operations were performed using a narrow linewidth diode laser. We employed a master-slave configuration for the laser, where an ultra low expansion glass Fabry-Perot cavity is used as a stable reference as well as a spectral filter. We characterized the laser spectrum using the ions with a modified Ramsey sequence which eliminated the affect of the magnetic field noise. We demonstrated high fidelity single qubit gates with individual addressing, based on inhomogeneous micromotion, on a two-ion chain as well as the Mølmer-Sørensen two-qubit entangling gate.

  • Orientation and alignment echoes

    Karras G., Hertz E., Billard F., Lavorel B., Hartmann J. -., Faucher O., Gershnabel E., Prior Y. & Averbukh I. S. (2015) Physical review letters.
    We present one of the simplest classical systems featuring the echo phenomenon - a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation or alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by the kick-induced filamentation of phase space, and provide the first experimental demonstration of classical alignment echoes in a thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses.

  • A simple model explaining super-resolution in absolute optical instruments

    Leonhardt U., Sahebdivan S., Kogan A. & Tyc T. (2015) New Journal of Physics.
    We develop a simple, one-dimensional model for super-resolution in absolute optical instruments that is able to describe the interplay between sources and detectors. Our model explains the subwavelength sensitivity of a point detector to a point source reported in previous computer simulations and experiments (Miñano 2011 New J. Phys.13 125009; Miñano 2014 New J. Phys.16 033015).

  • Attosecond tunnelling interferometry

    Pedatzur O., Orenstein G., Serbinenko V., Soifer H., Bruner B., Uzan A., Brambila D., Harvey A., Torlina L., Morales F., Smirnova O. & Dudovich N. (2015) Nature Physics.
    Attosecond physics offers new insights into ultrafast quantum phenomena involving electron dynamics on the fastest measurable timescales. The rapid progress in this field enables us to re-visit one of the most fundamental strong-field phenomena: field-induced tunnel ionization. In this work, we employ high-harmonic generation to probe the electron wavefunction during field-induced tunnelling through a potential barrier. By using a combination of strong and weak driving laser fields, we modulate the atomic potential barrier on optical subcycle timescales. This induces a temporal interferometer between attosecond bursts originating from consecutive laser half-cycles. Our study provides direct insight into the basic properties of field-induced tunnelling, following the evolution of the electronic wavefunction within a temporal window of approximately 200 €‰attoseconds.

  • Laser-induced cooling of broadband heat reservoirs

    Gelbwaser-Klimovsky D., Szczygielski K., Vogl U., Sass A., Alicki R., Kurizki G. & Weitz M. (2015) Physical Review A.
    We explore, theoretically and experimentally, a method for cooling a broadband heat reservoir, via its laser-assisted collisions with two-level atoms followed by their fluorescence. This method is shown to be advantageous compared to existing laser-cooling methods in terms of its cooling efficiency, the lowest attainable temperature for broadband baths, and its versatility: it can cool down any heat reservoir, provided the laser is red detuned from the atomic resonance. It is applicable to cooling down both dense gaseous and condensed media.

  • Measurement of the Spin-Dipolar Part of the Tensor Polarizability of Rb 87

    Dallal Y. & Ozeri R. (2015) Physical review letters.
    We report on the measurement of the contribution of the magnetic-dipole hyperfine interaction to the tensor polarizaility of the electronic ground state in Rb87. This contribution was isolated by measuring the differential shift of the clock transition frequency in Rb87 atoms that were optically trapped in the focus of an intense CO2 laser beam. By comparing to previous tensor polarizability measurements in Rb87, the contribution of the interaction with the nuclear electric-quadrupole moment was isolated as well. Our measurement will enable better estimation of blackbody shifts in Rb atomic clocks. The methods reported here are applicable for future spectroscopic studies of atoms and molecules under strong quasistatic fields.

  • Excited-state wavepacket and potential reconstruction by coherent anti-Stokes Raman scattering

    Avisar D. & Tannor D. (2015) Physical Chemistry Chemical Physics.
    Among the major challenges in the chemical sciences is controlling chemical reactions and deciphering their mechanisms. Since much of chemistry occurs in excited electronic states, in the last three decades scientists have employed a wide variety of experimental techniques and theoretical methods to recover excited-state potential energy surfaces and the wavepackets that evolve on them. These methods have been partially successful but generally do not provide a complete reconstruction of either the excited state wavepacket or potential. We have recently proposed a methodology for reconstructing excited-state molecular wavepackets and the corresponding potential energy surface [Avisar and Tannor, Phys. Rev. Lett., 2011, 106, 170405]. In our approach, the wavepacket is represented as a superposition of the set of vibrational eigenfunctions of the molecular ground-state Hamiltonian. We assume that the multidimensional ground-state potential surface is known, and therefore these vibrational eigenfunctions are known as well. The time-dependent coefficients of the basis functions are obtained by experimental measurement of the resonant coherent anti-Stokes Raman scattering (CARS) signal. Our reconstruction strategy has several significant advantages: (1) the methodology requires no a priori knowledge of any excited-state potential. (2) It applies to dissociative as well as to bound excited-state potentials. (3) It is general for polyatomics. (4) The excited-state potential surface is reconstructed simultaneously with the wavepacket. Apart from making a general contribution to the field of excited-state spectroscopy, our method provides the information on the excited-state wavepacket and potential necessary to design laser pulse sequences to control photochemical reactions.

  • Tailoring the Shape of Metallic Nanocavities for Enhanced Four-Wave Mixing

    Almeida E. & Prior Y. (2015) .
    Efficient four-wave mixing, with nonlinear response equivalent to BBO of the same thickness, is demonstrated for arrays of nanocavities milled in a free-standing gold film when their shape is properly designed.

  • Quantum technologies with hybrid systems

    Kurizki G., Bertet P., Kubo Y., Molmer K., Petrosyan D., Rabl P. & Schmiedmayer J. (2015) Proceedings of the National Academy of Sciences of the United States of America.
    An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field.

  • Magneto-Optical Properties of Paramagnetic Superrotors

    Milner A. A., Korobenko A., Floss J., Averbukh I. S. & Milner V. (2015) Physical review letters.
    We study the dynamics of paramagnetic molecular superrotors in an external magnetic field. An optical centrifuge is used to create dense ensembles of oxygen molecules in ultrahigh rotational states. In is shown, for the first time, that the gas of rotating molecules becomes optically birefringent in the presence of a magnetic field. The discovered effect of "magneto-rotational birefringence" indicates the preferential alignment of molecular axes along the field direction. We provide an intuitive qualitative model, in which the influence of the applied magnetic field on the molecular orientation is mediated by the spin-rotation coupling. This model is supported by the direct imaging of the distribution of molecular axes, the demonstration of the magnetic reversal of the rotational Raman signal, and by numerical calculations.

  • Diffraction manipulation by four-wave mixing

    Katzir I., Ron A. & Firstenberg O. (2015) Optics Express.
    We suggest a scheme to manipulate paraxial diffraction by utilizing the dependency of a four-wave mixing process on the relative angle between the light fields. A microscopic model for four-wave mixing in a.-type level structure is introduced and compared to recent experimental data. We show that images with feature size as low as 10 mu m can propagate with very little or even negative diffraction. The mechanism is completely different from that conserving the shape of spatial solitons in nonlinear media, as here diffraction is suppressed for arbitrary spatial profiles. At the same time, the gain inherent to the nonlinear process prevents loss and allows for operating at high optical depths. Our scheme does not rely on atomic motion and is thus applicable to both gaseous and solid media.

  • de Finetti reductions for correlations

    Arnon-Friedman R. & Renner R. (2015) Journal of Mathematical Physics.
    When analysing quantum information processing protocols, one has to deal with large entangled systems, each consisting of many subsystems. To make this analysis feasible, it is often necessary to identify some additional structures. de Finetti theorems provide such a structure for the case where certain symmetries hold. More precisely, they relate states that are invariant under permutations of subsystems to states in which the subsystems are independent of each other. This relation plays an important role in various areas, e.g., in quantum cryptography or state tomography, where permutation invariant systems are ubiquitous. The known de Finetti theorems usually refer to the internal quantum state of a system and depend on its dimension. Here, we prove a different de Finetti theorem where systems are modelled in terms of their statistics under measurements. This is necessary for a large class of applications widely considered today, such as device independent protocols, where the underlying systems and the dimensions are unknown and the entire analysis is based on the observed correlations. (C) 2015 Author(s).

  • Demonstration of deterministic photon -photon interactions with a single atom

    Rosenblum S., Shomroni I., Lovsky Y., Bechler O., Guendelman G. & Dayan B. (2015) .
    We demonstrate all-optical deterministic photon-atom and photon-photon interactions with a single Rb atom coupled to high-Q fiber-coupled microresonator. This scheme enables all-optical photon routing, passive quantum memory and quantum gates activated solely by single photons.

  • Relaxometry and Dephasing Imaging of Superparamagnetic Magnetite Nanoparticles Using a Single Qubit

    Schmid-Lorch D., Haeberle T., Reinhard F., Zappe A., Slota M., Bogani L., Finkler A. & Wrachtrup J. (2015) Nano Letters.
    To study the magnetic dynamics of superparamagnetic nanoparticles, we use scanning probe relaxometry and dephasing of the nitrogen vacancy (NV) center in diamond, characterizing the spin noise of a single 10 nm magnetite particle. Additionally, we show the anisotropy of the NV sensitivity's dependence on the applied decoherence measurement method. By comparing the change in relaxation (T-1) and dephasing (T-2) time in the NV center when scanning a nanoparticle over it, we are able to extract the nanoparticle's diameter and distance from the NV center using an Ornstein- Uhlenbeck model for the nanoparticle's fluctuations. This scanning probe technique can be used in the future to characterize different spin label substitutes for both medical applications and basic magnetic nanoparticle behavior.

  • Fractional quantum Hall states of Rydberg polaritons

    Maghrebi M. F., Yao N. Y., Hafezi M., Pohl T., Firstenberg O. & Gorshkov A. V. (2015) Physical Review A.
    We propose a scheme for realizing fractional quantum Hall states of light. In our scheme, photons of two polarizations are coupled to different atomic Rydberg states to form two flavors of Rydberg polaritons that behave as an effective spin. An array of optical cavity modes overlapping with the atomic cloud enables the realization of an effective spin-1/2 lattice. We show that the dipolar interaction between such polaritons, inherited from the Rydberg states, can be exploited to create a flat, topological band for a single spin-flip excitation. At half filling, this gives rise to a photonic (or polaritonic) fractional Chern insulator - a lattice-based, fractional quantum Hall state of light.

  • Shock assisted ionization injection in laser-plasma accelerators

    Thaury C., Guillaume E., Lifschitz A., Phuoc K. T., Hansson M., Grittani G., Gautier J., Goddet J. -., Tafzi A., Lundh O. & Malka V. (2015) Scientific Reports.
    Ionization injection is a simple and efficient method to trap an electron beam in a laser plasma accelerator. Yet, because of a long injection length, this injection technique leads generally to the production of large energy spread electron beams. Here, we propose to use a shock front transition to localize the injection. Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock. This simple technique leads to very stable and reliable injection even for modest laser energy. It should therefore become a unique tool for the development of laser-plasma accelerators.

  • Conversion of out-of-phase to in-phase order in coupled laser arrays with second harmonics

    Tradonsky C., Nixon M., Ronen E., Pal V., Chriki R., Friesem A. A. & Davidson N. (2015) Photonics Research.
    A novel method for converting an array of out-of-phase lasers into one of in-phase lasers that can be tightly focused is presented. The method exploits second-harmonic generation and can be adapted for different laser arrays geometries. Experimental and calculated results, presented for negatively coupled lasers formed in a square, honeycomb, and triangular geometries are in good agreement.

  • Van der Waals and Casimir–Polder dispersion forces

    Shahmoon E. (2015) .

  • Single-beam spectrally controlled two-dimensional Raman spectroscopy

    Frostig H., Bayer T., Dudovich N., Eldar Y. C. & Silberberg Y. (2015) Nature Photonics.
    Vibrational modes are often localized in certain regions of a molecule, and so the coupling between these modes is sensitive to the molecular structure. Two-dimensional vibrational spectroscopy can probe the strength of this coupling in a manner analogous to two-dimensional NMR spectroscopy, but on ultrafast timescales. Here, we demonstrate how two-dimensional Raman spectroscopy, based on fifth-order optical nonlinearity, can be performed with a single beam of shaped femtosecond optical pulses. Our spectroscopy scheme offers not only a major simplification of the conventional set-up, but also an inherent elimination of a competing nonlinear signal, which overwhelms the desired signal in other schemes and carries no coupling information.

  • Physics of fully-loaded laser-plasma accelerators

    Guillaume E., Doepp A., Thaury C., Lifschitz A., Goddet J., Tafzi A., Sylla F., Iaquanello G., Lefrou T., Rousseau P., Ta Phuoc K. & Malka V. (2015) Physical Review Special Topics-Accelerators And Beams.
    While large efforts have been devoted to improving the quality of electron beams from laser plasma accelerators, often to the detriment of the charge, many applications do not require very high quality but high-charge beams. Despite this need, the acceleration of largely charged beams has been barely studied. Here we explore both experimentally and numerically the physics of highly loaded wakefield acceleration. We find that the shape of the electron spectra is strikingly independent of the laser energy, due to the emergence of a saturation effect induced by beamloading. A transition from quasi-Maxwellian spectra at high plasma densities to flatter spectra at lower densities is also found, which is shown to be produced by the wakefield driven by the electron bunch itself after the laser depletion.

  • Cavity ring-up spectroscopy for ultrafast sensing with optical microresonators

    Rosenblum S., Lovsky Y., Arazi L., Vollmer F. & Dayan B. (2015) Nature Communications.
    Spectroscopy of whispering-gallery mode microresonators has become a powerful scientific tool, enabling the detection of single viruses, nanoparticles and even single molecules. Yet the demonstrated timescale of these schemes has been limited so far to milliseconds or more. Here we introduce a scheme that is orders of magnitude faster, capable of capturing complete spectral snapshots at nanosecond timescales - cavity ring-up spectroscopy. Based on sharply rising detuned probe pulses, cavity ring-up spectroscopy combines the sensitivity of heterodyne measurements with the highest-possible, transform-limited acquisition rate. As a demonstration, we capture spectra of microtoroid resonators at time intervals as short as 16 ns, directly monitoring submicrosecond dynamics of their optomechanical vibrations, thermorefractive response and Kerr nonlinearity. Cavity ring-up spectroscopy holds promise for the study of fast biological processes such as enzyme kinetics, protein folding and light harvesting, with applications in other fields such as cavity quantum electrodynamics and pulsed optomechanics.

  • Quantum mechanically enhanced performance of simple heat machines

    Gelbwaser-Klimovsky D. & Kurizki G. (2015) Physica Scripta T.
    We revisit the thermodynamic bounds of work extraction in simple quantum heat machines subject to control by frequent modulations that do not comply with adiabatic assumptions. The laws of thermodynamics are obeyed, yet anomalous deviations from the known bounds are revealed.

  • Work extraction from heat-powered quantized optomechanical setups

    Gelbwaser-Klimovsky D. & Kurizki G. (2015) Scientific Reports.
    We analyze work extraction from an autonomous (self-contained) heat-powered optomechanical setup. The initial state of the quantized mechanical oscillator plays a key role. As the initial mean amplitude of the oscillator decreases, the resulting efficiency increases. In contrast to laser-powered self-induced oscillations, work extraction from a broadband heat bath does not require coherence or phase-locking: an initial phase-averaged coherent state of the oscillator still yields work, as opposed to an initial Fock-state.

  • Observation of dynamical localization and bloch oscillations within molecular alignment of nitrogen

    Kamalov A., Floß J., Broege D. W., Averbukh I. S. & Bucksbaum P. H. (2015) .
    Nitrogen gas is rotationally excited by a train of eight impulsive kicks. The resulting population alignment evolution exhibits two phenomena explained by analogy to the famous condensed matter effects of dynamical localization and Bloch oscillations.

  • Phase locking of even and odd number of lasers on a ring geometry: Effects of topological-charge

    Pal V., Trandonsky C., Chriki R., Barach G., Friesem A. & Davidson N. (2015) Optics Express.
    The effects of topological charge on phase locking an array of coupled lasers are presented. This is done with even and odd number of lasers arranged on a ring geometry. With an even number of lasers the topological-charge effect is negligible, whereas with an odd number of lasers the topological-charge effect is clearly detected. Experimental and calculated results show how the topological charge effects degrade the quality of the phase locking, and how they can be removed. Our results shed further light on the frustration and also the quality of phase locking of coupled laser arrays.

  • Manipulating the spatial coherence of a laser source

    Chriki R., Nixon M., Pal V., Tradonsky C., Barach G., Friesem A. & Davidson N. (2015) Optics Express.
    An efficient method for controlling the spatial coherence has previously been demonstrated in a modified degenerate cavity laser. There, the degree of spatial coherence was controlled by changing the size of a circular aperture mask placed inside the cavity. In this paper, we extend the method and perform general manipulation of the spatial coherence properties of the laser, by resorting to more sophisticated intra-cavity masks. As predicted from the Van Cittert Zernike theorem, the spatial coherence is shown to depend on the geometry of the masks. This is demonstrated with different mask geometries: a variable slit which enables independent control of spatial coherence properties in one coordinate axis without affecting those in the other; a double aperture, an annular ring and a circular aperture array which generate spatial coherence functional forms of cosine, Bessel and comb, respectively. (C) 2015 Optical Society of America

  • Nonlinear light propagation in cholesteric liquid crystals with a helical Bragg microstructure

    Liu Y., Fu S., Zhu X., Xie X., Feng M., Zhou J., Li Y., Xiang Y., Malomed B. & Kurizki G. (2015) Journal of Optics (United Kingdom).
    Nonlinear optical propagation in cholesteric liquid crystals (CLC) with a spatially periodic helical molecular structure is studied experimentally and modeled numerically. This periodic structure can be seen as a Bragg grating with a propagation stopband for circularly polarized light. The CLC nonlinearity can be strengthened by adding absorption dye, thus reducing the nonlinear intensity threshold and the necessary propagation length. As the input power increases, a blue shift of the stopband is induced by the self-defocusing nonlinearity, leading to a substantial enhancement of the transmission and spreading of the beam. With further increase of the input power, the self-defocusing nonlinearity saturates, and the beam propagates as in the linear-diffraction regime. A system of nonlinear couple-mode equations is used to describe the propagation of the beam. Numerical results agree well with the experiment findings, suggesting that modulation of intensity and spatial profile of the beam can be achieved simultaneously under low input intensities in a compact CLC-based micro-device.

  • On cosmology in the laboratory.

    Leonhardt U. (2015) Philosophical transactions. Series A, Mathematical, physical, and engineering sciences.
    In transformation optics, ideas from general relativity have been put to practical use for engineering problems. This article asks the question how this debt can be repaid. In discussing a series of recent laboratory experiments, it shows how insights from wave phenomena shed light on the quantum physics of the event horizon.

  • Structural Basis for the Brilliant Colors of the Sapphirinid Copepods

    Gur D., Leshem B., Pierantoni M., Farstey V., Oron D., Weiner S. & Addadi L. (2015) Journal of the American Chemical Society.
    Males of sapphirinid copepods use regularly alternating layers of hexagonal-shaped guanine crystals and cytoplasm to produce spectacular structural colors. In order to understand the mechanism by which the different colors are produced, we measured the reflectance of live individuals and then characterized the organization of the crystals and the cytoplasm layers in the same individuals using cryo-SEM. On the basis of these measurements, we calculated the expected reflectance spectra and found that they are strikingly similar to the measured ones. We show that variations in the cytoplasm layer thickness are mainly responsible for the different reflected colors and also that the copepod color strongly depends on the angular orientation relative to the incident light, which can account for its appearance and disappearance during spiral swimming in the natural habitat.

  • Constraints on Exotic Dipole-Dipole Couplings between Electrons at the Micrometer Scale

    Kotler S., Ozeri R. & Kimball D. F. J. (2015) Physical review letters.
    New constraints on exotic dipole-dipole interactions between electrons at the micrometer scale are established, based on a recent measurement of the magnetic interaction between two trapped 88 Sr + ions. For light bosons (mass ≤ 0.1eV) we obtain a 90% confidence interval for an axial-vector-mediated interaction strength of |geAgeA/4πℏc|≤1.2×10−17. Assuming CPT invariance, this constraint is compared to that on anomalous electron-positron interactions, derived from positronium hyperfine spectroscopy. We find that the electron-electron constraint is 6 orders of magnitude more stringent than the electron-positron counterpart. Bounds on pseudoscalar-mediated interaction as well as on torsion gravity are also derived and compared with previous work performed at different length scales. Our constraints benefit from the high controllability of the experimental system which contained only two trapped particles. It therefore suggests a useful new platform for exotic particle searches, complementing other experimental efforts.

  • Collisional dynamics in a gas of molecular super-rotors

    Khodorkovsky Y., Steinitz U., Hartmann J. & Averbukh I. S. (2015) Nature Communications.
    Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable 'gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the 'gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules.

  • Spatial properties of odd and even low order harmonics generated in gas

    Lambert G., Andreev A., Gautier J., Giannessi L., Malka V., Petralia A., Sebban S., Stremoukhov S., Tissandier F., Vodungbo B. & Zeitoun P. (2015) Scientific Reports.
    High harmonic generation in gases is developing rapidly as a soft X-ray femtosecond light-source for applications. This requires control over all the harmonics characteristics and in particular, spatial properties have to be kept very good. In previous literature, measurements have always included several harmonics contrary to applications, especially spectroscopic applications, which usually require a single harmonic. To fill this gap, we present here for the first time a detailed study of completely isolated harmonics. The contribution of the surrounding harmonics has been totally suppressed using interferential filtering which is available for low harmonic orders. In addition, this allows to clearly identify behaviors of standard odd orders from even orders obtained by frequency-mixing of a fundamental laser and of its second harmonic. Comparisons of the spatial intensity profiles, of the spatial coherence and of the wavefront aberration level of 5 omega at 160 nm and 6 omega at 135 nm have then been performed. We have established that the fundamental laser beam aberrations can cause the appearance of a non-homogenous donut-shape in the 6 omega spatial intensity distribution. This undesirable effect can be easily controlled. We finally conclude that the spatial quality of an even harmonic can be as excellent as in standard generation.

  • Single-pulse Two-dimensional Raman Spectroscopy

    Frostig H., Bayer T., Dudovich N., Eldar Y. C. & Silberberg Y. (2015) .
    We present a single-pulse two-dimensional Raman spectroscopy scheme. Our scheme offers not only a major simplification of the conventional setup but also an inherent favoring of the direct fifth-order signal over the cascaded signal, the latter being a signal that carries no coupling information.

  • Rapid Manipulation of the Spatial Coherence

    Chriki R., Nixon M., Pal V., Tradonsky C., Barach G., Friesem A. A. & Davidson N. (2015) .
    Efficient method for manipulating the spatial coherence of a laser is presented. Different mutual intensity coherence functions, such as cosine or Bessel functions, are obtained, and number of modes is controlled in 1D and 2D.

  • Performance limits of multilevel and multipartite quantum heat machines

    Niedenzu W., Gelbwaser-Klimovsky D. & Kurizki G. (2015) Physical Review E.
    We present the general theory of a quantum heat machine based on an N-level system (working medium) whose N-1 excited levels are degenerate, a prerequisite for steady-state interlevel coherence. Our goal is to find out the extent to which coherence in the working medium is an asset for heat machines. The performance bounds of such a machine are common to (reciprocating) cycles that consist of consecutive strokes and continuous cycles wherein the periodically driven system is constantly coupled to cold and hot heat baths. Intriguingly, we find that the machine's performance strongly depends on the relative orientations of the transition-dipole vectors in the system. Perfectly aligned (parallel) transition dipoles allow for steady-state coherence effects, but also give rise to dark states, which hinder steady-state thermalization and thus reduce the machine's performance. Similar thermodynamic properties hold for N two-level atoms conforming to the Dicke model. We conclude that level degeneracy, but not necessarily coherence, is a thermodynamic resource, equally enhancing the heat currents and the power output of the heat machine. By contrast, the efficiency remains unaltered by this degeneracy and adheres to the Carnot bound.

  • Power enhancement of heat engines via correlated thermalization in a three-level "working fluid"

    Gelbwaser-Klimovsky D., Niedenzu W., Brumer P. & Kurizki G. (2015) Scientific Reports.
    We explore means of maximizing the power output of a heat engine based on a periodically-driven quantum system that is constantly coupled to hot and cold baths. It is shown that the maximal power output of such a heat engine whose "working fluid" is a degenerate V-type three-level system is that generated by two independent two-level systems. Hence, level degeneracy is a thermodynamic resource that may effectively double the power output. The efficiency, however, is not affected. We find that coherence is not an essential asset in such multilevel-based heat engines. The existence of two thermalization pathways sharing a common ground state suffices for power enhancement.

  • A spectral unaveraged algorithm for free electron laser simulations

    Andriyash I. A., Lehe R. & Malka V. (2015) Journal of Computational Physics.
    We propose and discuss a numerical method to model electromagnetic emission from the oscillating relativistic charged particles and its coherent amplification. The developed technique is well suited for free electron laser simulations, but it may also be useful for a wider range of physical problems involving resonant field-particles interactions. The algorithm integrates the unaveraged coupled equations for the particles and the electromagnetic fields in a discrete spectral domain. Using this algorithm, it is possible to perform full three-dimensional or axisymmetric simulations of short-wavelength amplification. In this paper we describe the method, its implementation, and we present examples of free electron laser simulations comparing the results with the ones provided by commonly known free electron laser codes.

  • Amplified short-wavelength light scattered by relativistic electrons in the laser-induced optical lattice

    Andriyash I. A., Tikhonchuk V. T., Malka V., D'Humieres E. & Balcou P. (2015) Physical Review Special Topics-Accelerators And Beams.
    The scheme of the x-ray free electron laser based on the optical undulator created by two overlapped transverse laser beams is analyzed. A kinetic theoretical description and an ad hoc numerical model are developed to account for the finite energy spread, angular divergence, and the spectral properties of the electron beam in the optical lattice. The theoretical findings are compared to the results of the one- and three-dimensional numerical modeling with the spectral free electron laser code PLARES.

  • The Mechanism of Color Change in the Neon Tetra Fish: A Light-Induced Tunable Photonic Crystal Array

    Gur D., Palmer B. A., Leshem B., Oron D., Fratzl P., Weiner S. & Addadi L. (2015) Angewandte Chemie (International ed. in English).
    The fresh water fish neon tetra has the ability to change the structural color of its lateral stripe in response to a change in the light conditions, from blue-green in the light-adapted state to indigo in the dark-adapted state. The colors are produced by constructive interference of light reflected from stacks of intracellular guanine crystals, forming tunable photonic crystal arrays. We have used micro X-ray diffraction to track in time distinct diffraction spots corresponding to individual crystal arrays within a single cell during the color change. We demonstrate that reversible variations in crystal tilt within individual arrays are responsible for the light-induced color variations. These results settle a long-standing debate between the two proposed models, the "Venetian blinds" model and the "accordion" model. The insight gained from this biogenic light-induced photonic tunable system may provide inspiration for the design of artificial optical tunable systems.

  • Table-top femtosecond soft X-ray laser by collisional ionization gating

    Depresseux A., Oliva E., Gautier J., Tissandier F., Nejdl J., Kozlova M., Maynard G., Goddet J. P., Tafzi A., Lifschitz A., Kim H. T., Jacquemot S., Malka V., Phuoc K. T., Thaury C., Rousseau P., Iaquaniello G., Lefrou T., Flacco A., Vodungbo B., Lambert G., Rousse A., Zeitoun P. & Sebban S. (2015) Nature Photonics.
    The advent of X-ray free-electron lasers has granted researchers an unprecedented access to the ultrafast dynamics of matter on the nanometre scale(1-3). Aside from being compact, seeded plasma-based soft X-ray lasers (SXRLs) turn out to be enticing as photon-rich(4) sources (up to 10(15) per pulse) that display high-quality optical properties(5,6). Hitherto, the duration of these sources was limited to the picosecond range(7), which consequently restricts the field of applications. This bottleneck was overcome by gating the gain through ultrafast collisional ionization in a high-density plasma generated by an ultraintense infrared pulse (a few 10(18) W cm(-2)) guided in an optically pre-formed plasma waveguide. For electron densities that ranged from 3 x 10(18) cm(-3) to 1.2 x 10(20) cm(-3), the gain duration was measured to drop from 7 ps to an unprecedented value of about 450 fs, which paves the way to compact and ultrafast SXRL beams with performances previously only accessible in large-scale facilities.

  • Coulomb Bound States of Strongly Interacting Photons

    Maghrebi M. F., Gullans M. J., Bienias P., Choi S., Martin I., Firstenberg O., Lukin M. D., Buechler H. P. & Gorshkov A. V. (2015) Physical Review Letters.
    We show that two photons coupled to Rydberg states via electromagnetically induced transparency can interact via an effective Coulomb potential. This interaction gives rise to a continuum of two-body bound states. Within the continuum, metastable bound states are distinguished in analogy with quasibound states tunneling through a potential barrier. We find multiple branches of metastable bound states whose energy spectrum is governed by the Coulomb potential, thus obtaining a photonic analogue of the hydrogen atom. Under certain conditions, the wave function resembles that of a diatomic molecule in which the two polaritons are separated by a finite “bond length.” These states propagate with a negative group velocity in the medium, allowing for a simple preparation and detection scheme, before they slowly decay to pairs of bound Rydberg atoms.

  • Experimental evidence for Abraham pressure of light

    Zhang L., She W., Peng N. & Leonhardt U. (2015) New Journal of Physics.
    The question of how much momentum light carries in media has been debated for over a century. Two rivalling theories, one from 1908 by Hermann Minkowski and the other from 1909 by Max Abraham, predict the exact opposite when light enters an optical material: a pulling force in Minkowski's case and a pushing force in Abraham's. Most experimental tests have agreed with Minkowski's theory, but here we report the first quantitative experimental evidence for Abraham's pushing pressure of light. Our results matter in optofluidics and optomechanics, and wherever light exerts mechanical pressure.

  • Phase Locking of Many Lasers by Combined Talbot Cavity and Fourier Filtering

    Tradonsky C., Pal V., Chriki R., Friesem A. A. & Davidson N. (2015) .
    Efficient in-phase coupling of hundreds of lasers by means of combined Talbot cavity and intra-cavity spatial Fourier filtering is developed. Simulated and experimental results for square, triangular and honeycomb laser arrays are presented.

  • Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources

    Lambert G., Vodungbo B., Gautier J., Mahieu B., Malka V., Sebban S., Zeitoun P., Luning J., Perron J., Andreev A., Stremoukhov S., Ardana-Lamas F., Dax A., Hauri C. P., Sardinha A. & Fajardo M. (2015) Nature Communications.
    Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far. We here show how this limitation is overcome by using a cross-polarized two-colour laser field. With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics. To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M-2,M-3 absorption edge around 67 eV. There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials.

  • Demonstration of relativistic electron beam focusing by a laser-plasma lens

    Thaury C., Guillaume E., Dopp A., Lehe R., Lifschitz A., Phuoc K. T., Gautier J., Goddet J., Tafzi A., Flacco A., Tissandier F., Sebban S., Rousse A. & Malka V. (2015) Nature Communications.
    Laser-plasma technology promises a drastic reduction of the size of high-energy electron accelerators. It could make free-electron lasers available to a broad scientific community and push further the limits of electron accelerators for high-energy physics. Furthermore, the unique femtosecond nature of the source makes it a promising tool for the study of ultrafast phenomena. However, applications are hindered by the lack of suitable lens to transport this kind of high-current electron beams mainly due to their divergence. Here we show that this issue can be solved by using a laser-plasma lens in which the field gradients are five order of magnitude larger than in conventional optics. We demonstrate a reduction of the divergence by nearly a factor of three, which should allow for an efficient coupling of the beam with a conventional beam transport line.

  • Thermodynamics of Quantum Systems Under Dynamical Control

    Gelbwaser-Klimovsky D., Niedenzu W. & Kurizki G. (2015) .
    In this review, the debated rapport between thermodynamics and quantum mechanics is addressed in the framework of the theory of periodically driven/controlled quantum-thermodynamic machines. The basic model studied here is that of a two-level system (TLS), whose energy is periodically modulated while the system is coupled to thermal baths. When the modulation interval is short compared to the bath memory time, the system-bath correlations are affected, thereby causing cooling or heating of the TLS, depending on the interval. In steady state, a periodically modulated TLS coupled to two distinct baths constitutes the simplest quantum heat machine (QHM) that may operate as either an engine or a refrigerator, depending on the modulation rate. We find their efficiency and power-output bounds and the conditions for attaining these bounds. An extension of this model to multilevel systems shows that the QHM power output can be boosted by the multilevel degeneracy.These results are used to scrutinize basic thermodynamic principles: (i) externally driven/modulated QHMs may attain the Carnot efficiency bound, but when the driving is done by a quantum device (piston), the efficiency strongly depends on its initial quantum state. Such dependence has been unknown thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the temperature approaches absolute zero for certain quantized baths, e.g., magnons, thus challenging Nernst's unattainability principle. (iii) System-bath correlations allow more work extraction under periodic control than that expected from the Szilard-Landauer principle, provided the period is in the non-Markovian domain. Thus, dynamically controlled QHMs may benefit from hitherto unexploited thermodynamic resources.

  • Enhanced Third-Harmonic Generation from a Metal/Semiconductor Core/Shell Hybrid Nanostructure

    Bar-Elli O., Grinvald E., Meir N., Neeman L. & Oron D. (2015) ACS Nano.
    Nonlinear optical processes can be dramatically enhanced via the use of localized surface plasmon modes in metal nanoparticles. Here we show how more elaborate structures, based on shape-controlled Au/Cu<sub>2</sub>O core/shell nanostructures, enable further enhancement of the nanoparticle third-harmonic scattering cross-section. The semiconducting component takes a twofold role in this structure, both providing a knob to tune the resonant frequency of the gold plasmon and providing resonant enhancement by virtue of its excitonic states. The advantages and deficiencies of using such core/shell metal/semiconductor structures are discussed.

  • Rational design of metallic nanocavities for resonantly enhanced four-wave mixing

    Almeida E. & Prior Y. (2015) Scientific Reports.
    Optimizing the shape of nanostructures and nano-antennas for specific optical properties has evolved to be a very fruitful activity. With modern fabrication tools a large variety of possibilities is available for shaping both nanoparticles and nanocavities; in particular nanocavities in thin metal films have emerged as attractive candidates for new metamaterials and strong linear and nonlinear optical systems. Here we rationally design metallic nanocavities to boost their Four-Wave Mixing response by resonating the optical plasmonic resonances with the incoming and generated beams. The linear and nonlinear optical responses as well as the propagation of the electric fields inside the cavities are derived from the solution of Maxwell's equations by using the 3D finite-differences time domain method. The observed conversion-efficiency of near-infrared to visible light equals or surpasses that of BBO of equivalent thickness. Implications to further optimization for efficient and broadband ultrathin nonlinear optical materials are discussed.

  • Observation of Bloch Oscillations in Molecular Rotation

    Floss J., Kamalov A., Averbukh I. & Bucksbaum P. H. (2015) Physical review letters.
    We report the observation of rotational Bloch oscillations in a gas of nitrogen molecules kicked by a periodic train of femtosecond laser pulses. A controllable detuning from the quantum resonance creates an effective accelerating potential in angular momentum space, inducing Bloch-like oscillations of the rotational excitation. These oscillations are measured via the temporal modulation of the refractive index of the gas. Our results introduce room-temperature laser-kicked molecules as a new laboratory for studies of localization phenomena in quantum transport.

  • Long-Lived Population Inversion in Isovalently Doped Quantum Dots

    Lahad O., Meir N., Pinkas I. & Oron D. (2015) ACS Nano.
    Optical gain from colloidal quantum dots has been desired for several decades since their discovery. While gain from multiexcitations is by now well-established, nonradiative Auger recombination limits the lifetime of such population inversion in quantum dots. CdSe cores isovalently doped by one to few Te atoms capped with rod-shaped CdS are examined as a candidate system for enhanced stimulated emission properties. Emission depletion spectroscopy shows a behavior characteristic of 3-level gain systems in these quantum dots. This implies complete removal of the 2-fold degeneracy of the lowest energy electronic excitation due to the large repulsive excitonexciton interaction in the doubly excited state. Using emission depletion measurements of the trap-associated emission from poorly passivated CdS quantum dots, we show that 3-level characteristics are typical of emission resulting from a band edge to trap state transition, but reveal subtle differences between the two systems. These results allow for unprecedented observation of long-lived population inversion from singly excited quantum dots.

  • Casimir forces in inhomogeneous media: towards a workable regularization

    Griniasty I. & Leonhardt U. (2015) .
    The most sophisticated theory of Casimir forces in realistic materials, Lifshitz theory, diverges in inhomogeneous media. Inspired by transformation optics, we have constructed a regularization procedure that appears to converge in planar materials.

  • Self-Assembled Organic Nanocrystals with Strong Nonlinear Optical Response

    Rosenne S., Grinvald E., Shirman E., Neeman L., Dutta S., Bar-Elli O., Ben-Zvi R., Oksenberg E., Milko P., Kalchenko V., Weissman H., Oron D. & Rybtchinski B. (2015) Nano Letters.
    Facile molecular self-assembly affords a new family of organic nanocrystals that, unintuitively, exhibit a significant nonlinear optical response (second harmonic generation, SHG) despite the relatively small molecular dipole moment of the constituent molecules. The nanocrystals are self-assembled in aqueous media from simple monosubstituted perylenediimide (PDI) molecular building blocks. Control over the crystal dimensions can be achieved via modification of the assembly conditions. The combination of a simple fabrication process with the ability to generate soluble SHG nanocrystals with tunable sizes may open new avenues in the area of organic SHG materials.

  • Spontaneous anti-Stokes backscattering in Brillouin dynamic gratings

    Yaron L., Shahmoon E., Bergman A., Langer T. & Tur M. (2015) .
    Spontaneous Brillouin backscattering, which accompanies the operation of Brillouin Dynamic Gratings (BDG) sensors, is experimentally investigated for the anti-stokes configuration, where the probe wave propagates against the orthogonally polarized high frequency writing pump. Even in the absence of the low frequency writing pump but for a strong enough high frequency writing pump, the observed anti-Stokes reflection of the probe becomes much stronger than its corresponding value under classical anti-Stokes backscattering. It is also shown that, eventually, as the probe reaches a critical value, the anti-Stokes reflection sharply decreases to its classical value.

  • Beam manipulation for compact laser wakefield accelerator based free-electron lasers

    Loulergue A., Labat M., Evain C., Benabderrahmane C., Malka V. & Couprie M. E. (2015) New Journal of Physics.
    Free-electron lasers (FELs) are a unique source of light, particularly in the x-ray domain. After the success of FELs based on conventional acceleration using radio-frequency cavities, an important challenge is the development of FELs based on electron bunching accelerated by a laser wakefield accelerator (LWFA). However, the present LWFA electron bunch properties do not permit use directly for a significant FEL amplification. It is known that longitudinal decompression of electron beams delivered by state-of-the-art LWFA eases the FEL process. We propose here a second order transverse beam manipulation turning the large inherent transverse chromatic emittances of LWFA beams into direct FEL gain advantage. Numerical simulations are presented showing that this beam manipulation can further enhance by orders of magnitude the peak power of the radiation.

  • Electron Rephasing in a Laser-Wakefield Accelerator

    Guillaume E., Doepp A., Thaury C., Phuoc K. T., Lifschitz A., Grittani G., Goddet J. -., Tafzi A., Chou S. W., Veisz L. & Malka V. (2015) Physical Review Letters.
    An important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%.

  • Persistence of magnetic field driven by relativistic electrons in a plasma

    Flacco A., Vieira J., Lifschitz A., Sylla F., Kahaly S., Veltcheva M., Silva L. O. & Malka V. (2015) Nature Physics.
    The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms(1), including instabilities(2,3), dynamo effects(4,5) and ultrahigh-energy particle flows through gas, plasma(6,7) and interstellar media(8,9). These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each process operates can be reconciled by scaling parameters that enable one to emulate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles in a laser-wakefield accelerator strongly magnetizes the boundary between plasma and non-ionized gas. We demonstrate, from time-resolved large-scale magnetic-field measurements and full-scale particle-in-cell simulations, the generation of strong magnetic fields up to 10-100 tesla (corresponding to nT in astrophysical conditions). These results open new paths for the exploration and modelling of ultrahigh-energy particle-driven magnetic-field generation in the laboratory.

  • Edge states of periodically kicked quantum rotors

    Floss J. & Averbukh I. S. (2015) Physical Review E.
    We present a quantum localization phenomenon that exists in periodically kicked three-dimensional rotors, but is absent in the commonly studied two-dimensional ones: edge localization. We show that under the condition of a fractional quantum resonance there are states of the kicked rotor that are strongly localized near the edge of the angular momentum space at J=0. These states are analogs of surface states in crystalline solids, and they significantly affect resonant excitation of molecular rotation by laser pulse trains.

  • Coherent Coupling of Alkali Atoms by Random Collisions

    Katz O., Peleg O. & Firstenberg O. (2015) Physical Review Letters.
    Random spin-exchange collisions in warm alkali vapor cause rapid decoherence and act to equilibrate the spin state of the atoms in the vapor. In contrast, here we demonstrate experimentally and theoretically a coherent coupling of one alkali species to another species, mediated by these random collisions. We show that the minor species (potassium) inherits the magnetic properties of the dominant species (rubidium), including its lifetime (T1),coherence time (T2), gyromagnetic ratio, and spin-exchange relaxation-free magnetic-field threshold. We further show that this coupling can be completely controlled by varying the strength of the magnetic field. Finally, we explain these phenomena analytically by mode mixing of the two species via spin-exchange collisions.

  • Atom-diatom scattering dynamics of spinning molecules

    Eyles C. J., Floss J., Averbukh I. S. & Leibscher M. (2015) Journal of Chemical Physics.
    We present full quantum mechanical scattering calculations using spinning molecules as target states for nuclear spin selective atom-diatom scattering of reactive D+H<sub>2</sub> and F+H<sub>2</sub> collisions. Molecules can be forced to rotate uni-directionally by chiral trains of short, non-resonant laser pulses, with different nuclear spin isomers rotating in opposite directions. The calculations we present are based on rotational wavepackets that can be created in this manner. As our simulations show, target molecules with opposite sense of rotation are predominantly scattered in opposite directions, opening routes for spatially and quantum state selective scattering of close chemical species. Moreover, two-dimensional state resolved differential cross sections reveal detailed information about the scattering mechanisms, which can be explained to a large degree by a classical vector model for scattering with spinning molecules.

  • Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation

    Ferre A., Boguslavskiy A. E., Dagan M., Blanchet V., Bruner B. D., Burgy F., Camper A., Descamps D., Fabre B., Fedorov N., Gaudin J., Geoffroy G., Mikosch J., Patchkovskii S., Petit S., Ruchon T., Soifer H., Staedter D., Wilkinson I., Stolow A., Dudovich N. & Mairesse Y. (2015) Nature Communications.
    High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF<sub>6</sub> as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected.

  • Demonstration of Deterministic Photon-photon Interactions with a Single Atom

    Rosenblum S., Shomroni I., Bechler O., Lovsky Y., Guendelman G. & Dayan B. (2015) .
    We demonstrate deterministic photon-atom and photon-photon interactions with a single atom coupled to a high-Q fiber-coupled microresonator. Based on Deterministic One Photon Raman Interaction (DOPRI), this scheme can form the basis for all-optical quantum information processing.

  • Thermal baths as quantum resources: More friends than foes?

    Kurizki G., Shahmoon E. & Zwick A. (2015) PHYSICA SCRIPTA.
    In this article we argue that thermal reservoirs (baths) are potentially useful resources in processes involving atoms interacting with quantized electromagnetic fields and their applications to quantum technologies. One may try to suppress the bath effects by means of dynamical control, but such control does not always yield the desired results. We wish instead to take advantage of bath effects, that do not obliterate 'quantumness' in the system-bath compound. To this end, three possible approaches have been pursued by us. (i) Control of a quantum system faster than the correlation time of the bath to which it couples: such control allows us to reveal quasi-reversible/coherent dynamical phenomena of quantum open systems, manifest by the quantum Zeno or anti-Zeno effects (QZE or AZE, respectively). Dynamical control methods based on the QZE are aimed not only at protecting the quantumness of the system, but also diagnosing the bath spectra or transferring quantum information via noisy media. By contrast, AZE-based control is useful for fast cooling of thermalized quantum systems. (ii) Engineering the coupling of quantum systems to selected bath modes: this approach, based on field-atom coupling control in cavities, waveguides and photonic band structures, allows one to drastically enhance the strength and range of atom-atom coupling through the mediation of the selected bath modes. More dramatically, it allows us to achieve bath-induced entanglement that may appear paradoxical if one takes the conventional view that coupling to baths destroys quantumness. (iii) Engineering baths with appropriate non-flat spectra: this approach is a prerequisite for the construction of the simplest and most efficient quantum heat machines (engines and refrigerators). We may thus conclude that often thermal baths are 'more friends than foes' in quantum technologies.