• 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.
  • 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.
  • 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.
  • 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)
    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.
  • 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) The 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)
    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)
    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., 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)
    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)
    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.
  • 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.

    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)
    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)
    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)
    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)
    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.
  • Quantum entangled states of a classically radiating macroscopic spin

    Somech O. & Shahmoon E. (2022)
    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.
  • 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)
    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.
  • 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.
  • 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.
  • 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) Optics InfoBase Conference Papers.
    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.
  • 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.
  • Mapping Single Electron Spins with Magnetic Tomography

    Yudilevich D., Stöhr R., Denisenko A. & Finkler A. (2022) Physical Review Applied.
    Mapping the positions of single electron spins is a highly desired capability for applications such as nanoscale magnetic resonance imaging and quantum network characterization. Here, we demonstrate a method based on rotating an external magnetic field to identify the precise location of single electron spins in the vicinity of a quantum spin sensor. We use a nitrogen-vacancy center in diamond as a quantum sensor and modulate the dipolar coupling to a proximate electron spin in the crystal by varying the magnetic field vector. The modulation of the dipolar coupling contains information on the coordinates of the spin, from which we extract its position with an uncertainty of 0.9 Å. We show that the method can be used to locate electron spins with nanometer precision up to 10 nm away from the sensor. We discuss the applicability of the method to mapping hyperfine coupled electron spins and show that it may be applied to locating nitroxide radicals. The magnetic tomography method can be utilized for distance measurements for studying the structure of individual molecules.
  • 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)
    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)
    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)
    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.
  • 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.
  • 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),

    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.
  • High-speed low-frequency chirped coherent anti-Stokes Raman scattering microscopy using an ultra-steep long-pass filter

    Ren L., Raanan D., Hurwitz I. & Oron D. (2019) Optics Express.
    Coherent anti-Stokes Raman scattering (CARS) microscopy is becoming a more common tool in biomedical research. High-speed CARS microscopy has important applications in live cell imaging and in label-free pathology. However, only a few realizations exist of CARS imaging applied in the few terahertz spectral range (
  • 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)
    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.
  • 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.
  • Enhanced precision bound of low-temperature quantum thermometry via dynamical control

    Mukherjee V., Zwick A., Ghosh A., Chen X. & Kurizki G. (2019) Communications Physics.
    High-precision low-temperature thermometry is a challenge for experimental quantum physics and quantum sensing. Here we consider a thermometer modeled by a dynamically-controlled multilevel quantum probe in contact with a bath. Dynamical control in the form of periodic modulation of the energy-level spacings of the quantum probe can dramatically increase the maximum accuracy bound of low-temperatures estimation, by maximizing the relevant quantum Fisher information. As opposed to the diverging relative error bound at low temperatures in conventional quantum thermometry, periodic modulation of the probe allows for low-temperature thermometry with temperature-independent relative error bound. The proposed approach may find diverse applications related to precise probing of the temperature of many-body quantum systems in condensed matter and ultracold gases, as well as in different branches of quantum metrology beyond thermometry, for example in precise probing of different Hamiltonian parameters in many-body quantum critical systems.
  • 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.
  • 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
  • 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.
  • 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 reversib