Publications

Programmable Quantum Simulations on a Trapped-Ion Quantum Computer with a Global Drive

Shapira Y., Markov J., Akerman N., Stern A. & Ozeri R. (2025) Physical Review Letters.

Simulation of quantum systems is notoriously challenging for classical computers, while quantum hardware is naturally well-suited for this task. However, the imperfections of contemporary quantum systems pose a considerable challenge in carrying out accurate simulations over long evolution times. Here, we experimentally demonstrate a method for quantum simulations on a small-scale trapped-ion-based quantum simulator. Our method enables quantum simulations of programmable spin-Hamiltonians, using only simple global fields, driving all qubits homogeneously and simultaneously. We measure the evolution of a quantum Ising ring and accurately reconstruct the Hamiltonian parameters, showcasing an accurate and high-fidelity simulation. Our method enables a significant reduction in the required control and depth of quantum simulations, thus generating longer evolution times with higher accuracy.

Programmable Quantum Simulations on a Trapped-Ion Quantum Computer with a Global Drive

Shapira Y., Markov J., Akerman N., Stern A. & Ozeri R. (2025) Physical Review Letters.

Simulation of quantum systems is notoriously challenging for classical computers, while quantum hardware is naturally well-suited for this task. However, the imperfections of contemporary quantum systems pose a considerable challenge in carrying out accurate simulations over long evolution times. Here, we experimentally demonstrate a method for quantum simulations on a small-scale trapped-ion-based quantum simulator. Our method enables quantum simulations of programmable spin-Hamiltonians, using only simple global fields, driving all qubits homogeneously and simultaneously. We measure the evolution of a quantum Ising ring and accurately reconstruct the Hamiltonian parameters, showcasing an accurate and high-fidelity simulation. Our method enables a significant reduction in the required control and depth of quantum simulations, thus generating longer evolution times with higher accuracy.

Operating a Multi-Ion Clock with Dynamical Decoupling

Akerman N. & Ozeri R. (2025) Physical Review Letters.

We study and characterize a quasicontinuous dynamical decoupling scheme that effectively suppresses dominant frequency shifts in a multi-ion optical clock. Addressing the challenge of inhomogeneous frequency shifts in such systems, our scheme mitigates primary contributors, namely, the electric quadrupole and the linear Zeeman shifts. Based on Sr+88 ions, we implement the scheme in linear chains of up to 7 ions and demonstrate a significant suppression of the shift by more than 3 orders of magnitude, leading to relative frequency inhomogeneity below 7×10-17. Additionally, we evaluate the associated systematic shift arising from the radio-frequency drive used in the QCDD scheme, showing that, in the presented realization, its contribution to the systematic relative frequency uncertainty is below 10-17, with the potential for further improvement. These results provide a promising avenue toward implementing multi-ion clocks exhibiting an order of magnitude or more improvement in stability while maintaining a similar high degree of accuracy to that of single-ion clocks.

Operating a Multi-Ion Clock with Dynamical Decoupling

Akerman N. & Ozeri R. (2025) Physical Review Letters.

We study and characterize a quasicontinuous dynamical decoupling scheme that effectively suppresses dominant frequency shifts in a multi-ion optical clock. Addressing the challenge of inhomogeneous frequency shifts in such systems, our scheme mitigates primary contributors, namely, the electric quadrupole and the linear Zeeman shifts. Based on Sr+88 ions, we implement the scheme in linear chains of up to 7 ions and demonstrate a significant suppression of the shift by more than 3 orders of magnitude, leading to relative frequency inhomogeneity below 7×10-17. Additionally, we evaluate the associated systematic shift arising from the radio-frequency drive used in the QCDD scheme, showing that, in the presented realization, its contribution to the systematic relative frequency uncertainty is below 10-17, with the potential for further improvement. These results provide a promising avenue toward implementing multi-ion clocks exhibiting an order of magnitude or more improvement in stability while maintaining a similar high degree of accuracy to that of single-ion clocks.

Simple few-shot method for spectrally resolving the wavefront of an ultrashort laser pulse

Smartsev S., Liberman A., Andriyash I. A., Cavagna A., Flacco A., Giaccaglia C., Kaur J., Monzac J., Tata S., Vernier A., Malka V., Lopez-Martens R. & Faure J. (2024) Optics Letters.

We present a novel, to the best of our knowledge, and straightforward approach for the spatio-spectral characterization of ultrashort pulses. This minimally intrusive method relies on placing a mask with specially arranged pinholes in the beam path before the focusing optic and retrieving the spectrally resolved laser wavefront from the speckle pattern produced at focus. We test the efficacy of this new method by accurately retrieving chromatic aberrations, such as pulse-front tilt (PFT), pulse-front curvature (PFC), and higher-order aberrations introduced by a spherical lens. The simplicity and scalability of this method, combined with its compatibility with single-shot operation, make it a strong complement to existing tools for high-intensity laser facilities.

The Future of Attosecond Science

Dudovich N., Fang L., Gaarde M., Keller U., Landsman A., Richter M., Rohringer N. & Young L. (2024) .

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

Improving correlation based super-resolution microscopy images through image fusion by self-supervised deep learning

Beck L. M., Shocher A., Rossman U., Halfon A., Irani M. & Oron D. (2024) Optics Express.

Super-resolution imaging is a powerful tool in modern biological research, allowing for the optical observation of subcellular structures with great detail. In this paper, we present a deep learning approach for image fusion of intensity and super-resolution optical fluctuation imaging (SOFI) microscopy images. We construct a network that can successfully combine the advantages of these two imaging methods, producing a fused image with a resolution comparable to that of SOFI and an SNR comparable to that of the intensity image. We also demonstrate the effectiveness of our approach experimentally, specifically on cell samples where microtubules were stained with ATTO647N and imaged using a confocal microscope with a single photon fiber bundle camera, allowing for the simultaneous acquisition of an image scanning microscopy (ISM) image and a SOFISM (ISM and SOFI) image. Our network is designed as a self-supervised network and shows the ability to train on a single pair of images and to generalize to other image pairs without the need for additional training. Our approach offers a flexible and efficient way to combine the strengths of correlation based imaging techniques along with traditional intensity based microscopy, and can be readily applied to other fluctuation based imaging modalities.

Technique to measure the gravitational mass of ultracold matter and its implications for antimatter studies

Raz B., Fleurov G., Holtzman R., Davidson N. & Sarid E. (2024) Physical Review A.

Measuring the effect of gravity on antimatter is a longstanding problem in physics that has significant implications for our understanding of the fundamental nature of the universe. Here, we present a technique to measure the gravitational mass of atoms, motivated by a recent measurement of antimatter atoms at CERN [Nature (London) 621, 716 (2023)0028-083610.1038/s41586-023-06527-1]. We demonstrate our technique on cold atoms by measuring the fraction of atoms that survive in the trap after gradually softening a quadrupole magnetic trap in a gravitational potential. We compare our measurements with a Monte Carlo simulation to extract the value of the gravitational acceleration. The difference between the accepted value for g, the local acceleration due to gravity, and the measured value is (-1.9±12stat±40syst)×10-4g. We demonstrate the importance of various design parameters in the experiment setup and estimate their contribution to the achievable accuracy in future experiments. Our method demonstrates simplicity, precision, and reliability, facilitating future precision studies of the gravitational force on antimatter. It can also be used to precisely calibrate atom traps based on the known gravitational attraction of ordinary matter to Earth.

Super-resolved coherent anti-Stokes Raman scattering microscopy by coherent image scanning

Zhitnitsky A., Benjamin E., Bitton O. & Oron D. (2024) Nature Communications.

We present super-resolved coherent anti-Stokes Raman scattering (CARS) microscopy by implementing phase-resolved image scanning microscopy, achieving up to two-fold resolution increase as compared with a conventional CARS microscope. Phase-sensitivity is required for the standard pixel-reassignment procedure since the scattered field is coherent, thus the point-spread function is well-defined only for the field amplitude. We resolve the complex field by a simple add-on to the CARS setup enabling inline interferometry. Phase-sensitivity offers additional contrast which informs the spatial distribution of both resonant and nonresonant scatterers. As compared with alternative super-resolution schemes in coherent nonlinear microscopy, the proposed method is simple, requires only low-intensity excitation, and is compatible with any conventional forward-detected CARS imaging setup.

Experimental quantum noise sensing via quantum Zeno/anti-Zeno effect

Virzì S., Knoll L. T., Piacentini F., Avella A., Gherardini S., Opatrný T., Kofman A. G., Kurizki G., Gramegna M., Caruso F., Degiovanni I. P. & Genovese M. (2024) .

We introduce and experimentally demonstrate two techniques allowing to extract information on the noise affecting single-photon probes propagating in a quantum channel, by exploiting quantum Zeno and anti-Zeno effects.

Advances in quantum imaging

Defienne H., Bowen W. P., Chekhova M., Lemos G. B., Oron D., Ramelow S., Treps N. & Faccio D. (2024) Nature Photonics.

Modern imaging technologies are widely based on classical principles of light or electromagnetic wave propagation. They can be remarkably sophisticated, with recent successes ranging from single-molecule microscopy to imaging far-distant galaxies. However, new imaging technologies based on quantum principles are gradually emerging. They can either surpass classical approaches or provide novel imaging capabilities that would not otherwise be possible. Here we provide an overview of the most recently developed quantum imaging systems, highlighting the nonclassical properties of sources, such as bright squeezed light, entangled photons and single-photon emitters that enable their functionality. We outline potential upcoming trends and the associated challenges, all driven by a central enquiry, which is to understand whether quantum light can make visible the invisible.

Guanidinium Substitution Improves Self-Healing and Photodamage Resilience of MAPbI3

Singh P., Ceratti D. R., Soffer Y., Bera S., Feldman Y., Elbaum M., Oron D., Cahen D. & Hodes G. (2024) Journal of Physical Chemistry C.

Self-healing materials can become game changers for developing sustainable (opto)electronics. APbX3 halide (=X-) perovskites, HaPs, have shown a remarkable ability to self-heal damage. While we demonstrated self-healing in pure HaP compounds, in single crystals, and in polycrystalline thin films (as used in most devices), HaP compositions with multiple A+ (and X-) constituents are preferred for solar cells. We now show self-healing in mixed A+ HaPs. Specifically, if at least 15 atom % of the methylammonium (MA+) A cation is substituted for by guanidinium (Gua+) or acetamidinium (AA+), then the self-healing rate after damage is enhanced. In contrast, replacing MA+ with dimethylammonium (DMA+), comparable in size to Gua+ or AA+, does not alter this rate. Based on the times for self-healing, we infer that the rate-determining step involves short-range diffusion of A+ and/or Pb2+ cations and that the self-healing rate correlates with the strain in the material, the A+ cation dipole moment, and H-bonding between A+ and I-. These insights may offer clues for developing a detailed self-healing mechanism and understanding the kinetics to guide the design of self-healing materials. Fast recovery kinetics are important from the device perspective, as they allow complete recovery in devices during operation or when switched off (LEDs)/in the dark (photovoltaics).

Technical Design Report for the LUXE experiment

Abramowicz H., Almanza Soto M., Altarelli M., Aßmann R., Athanassiadis A., Avoni G., Behnke T., Benettoni M., Benhammou Y., Bhatt J., Blackburn T., Blanch C., Bonaldo S., Boogert S., Borysova M., Epshteyn L., Kroupp E., Levinson L., Liberman A., Malka V., Santra A., Hod N. & Urmanov R. (2024) European Physical Journal: Special Topics.

This Technical Design Report presents a detailed description of all aspects of the LUXE (Laser Und XFEL Experiment), an experiment that will combine the high-quality and high-energy electron beam of the European XFEL with a high-intensity laser, to explore the uncharted terrain of strong-field quantum electrodynamics characterised by both high energy and high intensity, reaching the Schwinger field and beyond. The further implications for the search of physics beyond the Standard Model are also discussed.

Universal Approach for Quantum Interfaces with Atomic Arrays

Solomons Y., Ben-Maimon R. & Shahmoon E. (2024) PRX Quantum.

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.

First Electrons from Axiparabola-Based LWFA

Liberman A., Smartsev S., Tata S., Golovanov A., Benracassa S., Andriyash I., Lahaye R., Levine E. Y., Kroupp E., Thaury C. & Malka V. (2024) .

We present the first acceleration of electrons by an axiparabola-focused wakefield. This proof-of-concept experiment strengthens the argument for an axiparabola-based solution for dephasingless LWFA. We also show numerical simulations confirming the experimental results.

Recovering quantum coherence of a cavity qubit through environment monitoring and active feedback

Goldblatt U., Kahn N., Hazanov S., Milul O., Guttel B., Joshi L. M., Chausovsky D., Lafont F. & Rosenblum S. (2024) arXiv.org.

Decoherence in qubits, caused by their interaction with a noisy environment, poses a significant challenge to developing reliable quantum processors. Monitoring the qubit's environment enables not only to identify decoherence events but also to reverse these errors, thereby restoring the qubit coherence. This approach is particularly beneficial for superconducting cavity qubits, whose unavoidable interaction with auxiliary transmons impacts their coherence. In this work, we uncover the intricate dynamics of cavity decoherence by tracking the noisy trajectory of a transmon acting as the cavity's environment. Using real-time feedback, we successfully recover the lost coherence of the cavity qubit, achieving a fivefold increase in its dephasing time. Alternatively, by detecting transmon errors and converting them into erasures, we improve the cavity phase coherence by more than an order of magnitude. These advances are essential for implementing long-lived cavity qubits with high-fidelity gates and can enable more efficient bosonic quantum error correction codes.

Interface Engineering in a CdS-Modified PbS Nanosheet-FAPbI3 Heterostructure Enabling High-Performance Perovskite Solar Cells

Liu X., Zhong H., Wang X., Yang J., Zhang Z., Han J., Oron D. & Lin H. (2024) ACS Applied Materials and Interfaces.

Regulating strain in perovskite films via utilizing the crystal structure relationship between solid-phase materials (SPMs) and perovskite is an effective method to achieve high-performance perovskite solar cells. It is crucial to investigate and manipulate the heterointerfaces between perovskites and SPMs since the mismatched crystal structure and energy band structure of SPMs will bring recombination sites to the heterointerfaces. In this work, CdS-modified PbS nanosheets (CPS) were prepared through cation exchange with (200)-preferred PbS nanosheets. The wide-band gap CdS charge-blocking layer of CPS nanosheets distributed at the grain boundaries effectively passivates the heterointerfaces in FAPbI3-CPS heterostructures (FAPI-CPS). Further, it potentially blocks carrier transportation and suppresses carrier recombination at grain boundaries and in FAPbI3-PbS nanosheet heterointerfaces. Attributed to the CdS layer, the FAPI-CPS devices achieve an enhanced power conversion efficiency. CPS nanosheets with an interplanar spacing slightly smaller than that of α-FAPbI3 could provide compressive strain to FAPbI3 at the FAPI-CPS heterointerfaces, leading to significantly improved device stability. The unencapsulated FAPI-CPS solar cells maintained 92% of their initial PCE after being stored at 20 ± 5 °C, 20 ± 5% RH for 2500 h.

Quantum Entangled States of a Classically Radiating Macroscopic Spin

Somech O. & Shahmoon E. (2024) PRX Quantum.

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

Prospects of nuclear-coupled-dark-matter detection via correlation spectroscopy of I2+ and Ca+

Madge E., Perez G. & Meir Z. (2024) Physical Review D.

The nature of dark matter (DM) and its interaction with the Standard Model (SM) is one of the biggest open questions in physics nowadays. The vast majority of theoretically motivated ultralight-DM (ULDM) models predict that ULDM couples dominantly to the SM strong/nuclear sector. This coupling leads to oscillations of nuclear parameters that are detectable by comparing clocks with different sensitivities to these nature's constants. Vibrational transitions of molecular clocks are more sensitive to a change in the nuclear parameters than the electronic transitions of atomic clocks. Here, we propose the iodine molecular ion, I2+, as a sensitive detector for such a class of ULDM models. The iodine's dense spectrum allows us to match its transition frequency to that of an optical atomic clock (Ca+) and perform correlation spectroscopy between the two clock species. With this technique, we project a few-orders-of-magnitude improvement over the most sensitive clock comparisons performed to date. We also briefly consider the robustness of the corresponding "Earth-bound"under modifications of the ZN-QCD axion model.

Simple few-shot method for spectrally resolving the wavefront of an ultrashort laser pulse

Smartsev S., Liberman A., Andriyash I. A., Cavagna A., Flacco A., Giaccaglia C., Kaur J., Monzac J., Tata S., Vernier A., Malka V., Lopez-Martens R. & Faure J. (2024) .

We introduce a novel method for spatio-spectral characterization of ultrashort pulses. Our custom iterative algorithm, capable of color separation, retrieves phase information from speckles generated through a specialized pinhole mask.

Quantum noise in time-dependent media and cosmic expansion

Landau Z. & Leonhardt U. (2024) Physical Review B.

In spatially uniform, but time-dependent dielectric media with equal electric and magnetic response, classical electromagnetic waves propagate exactly like in empty, flat space with transformed time, called conformal time, and so do quantum fluctuations. In empty, flat space the renormalized vacuum energy is exactly zero, but not in time-dependent media, as we show in this paper. This is because renormalization is local and causal, and so cannot compensate fully for the transformation to conformal time. The expanding universe appears as such a medium to the electromagnetic field. We show that the vacuum energy during cosmic expansion effectively reduces the weights of radiation and matter by characteristic factors. This quantum buoyancy naturally resolves the Hubble tension, the discrepancy between the measured and the inferred Hubble constant, and it might resolve other cosmological tensions as well.

How to find optimal quantum states for optical micromanipulation and metrology in complex scattering problems: tutorial

Rachbauer L. M., Bouchet D., Leonhardt U. & Rotter S. (2024) Journal of the Optical Society of America B: Optical Physics.

The interaction of quantum light with matter is of great importance to a wide range of scientific disciplines, ranging from optomechanics to high-precision measurements. A central issue we discuss here, is how to make optimal use of both the spatial and the quantum degrees of freedom of light for characterizing and manipulating arbitrary observable parameters in a linear scattering system into which suitably engineered light fields are injected. Here, we discuss a comprehensive framework based on a quantum operator that can be assembled solely from the scattering matrix of a system and its dependence on the corresponding local parameter, making this operator experimentally measurable from the far field using only classical light. From this, the effect of quantum light in the near field, i.e., in the vicinity of the target object, can be inferred. Based on this framework, it is straightforward to formulate optimal protocols on how to jointly design both the spatial shape and the quantum characteristics of light for micromanipulation as well as for parameter estimation in arbitrarily complex media. Also, the forces of the quantum vacuum naturally emerge from this formalism. The aim of our tutorial is to bring different perspectives into alignment and thereby build a bridge between the different communities of wave control, quantum optics, micromanipulation, quantum metrology, and vacuum physics.

Quantum control of ion-atom collisions beyond the ultracold regime

Walewski M. Z., Frye M. D., Katz O., Pinkas M., Ozeri R. & Tomza M. (2024) arXiv.org.

Control of microscopic physical systems is a prerequisite for experimental quantum science and its applications. Neutral atomic and molecular systems can be controlled using tunable scattering resonances. However, the resonant control of effective interactions has so far been limited to the ultracold regime, where quantum effects become manifest. Ultracold temperatures are still out of reach for most hybrid trapped ion-atom systems, a prospective platform for quantum technologies and fundamental research. Here we show that magnetically tunable Feshbach resonances can be used to control inelastic collisions between a single trapped Sr+ ion and Rb atoms high above the ultracold regime. We measure inelastic collision probabilities and use the results to calibrate a comprehensive theoretical model of ion-atom collisions. The observed collision dynamics show signatures of quantum interference, resulting in the pronounced state and mass dependence of the collision rates in the multiple-partial-wave regime. With our model, we discover multiple measurable Feshbach resonances for magnetic fields from 0 to 400 G, which allow significant enhancement of spin-exchange rates at temperatures as high as 1 mK. Future observation of the predicted resonances should allow precise calibration and control of the short-range dynamics in the Sr++Rb collisions under unprecedentedly warm conditions.

Quantum control of ion-atom collisions beyond the ultracold regime

Walewski M. Z., Frye M. D., Katz O., Pinkas M., Ozeri R. & Tomza M. (2024) arXiv.org.

Control of microscopic physical systems is a prerequisite for experimental quantum science and its applications. Neutral atomic and molecular systems can be controlled using tunable scattering resonances. However, the resonant control of effective interactions has so far been limited to the ultracold regime, where quantum effects become manifest. Ultracold temperatures are still out of reach for most hybrid trapped ion-atom systems, a prospective platform for quantum technologies and fundamental research. Here we show that magnetically tunable Feshbach resonances can be used to control inelastic collisions between a single trapped Sr+ ion and Rb atoms high above the ultracold regime. We measure inelastic collision probabilities and use the results to calibrate a comprehensive theoretical model of ion-atom collisions. The observed collision dynamics show signatures of quantum interference, resulting in the pronounced state and mass dependence of the collision rates in the multiple-partial-wave regime. With our model, we discover multiple measurable Feshbach resonances for magnetic fields from 0 to 400 G, which allow significant enhancement of spin-exchange rates at temperatures as high as 1 mK. Future observation of the predicted resonances should allow precise calibration and control of the short-range dynamics in the Sr++Rb collisions under unprecedentedly warm conditions.

Attosecond Interferometry

Krüger M. & Dudovich N. (2024) .

In this chapter, we introduce all-optical attosecond interferometry using high-harmonic generation (HHG). Interferometry provides an access to phase information, enabling the reconstruction of ultrafast electron dynamics with attosecond precision. We discuss two main pathwaysinternal and external attosecond interferometry. In internal interferometry, the manipulation of quantum paths within the HHG mechanism enables phase-resolved studies of strong-field processes, such as field-induced tunneling. In external interferometry, the phase of the light emitted during the HHG process can be determined using optical interference in the extreme-ultraviolet regime. Both pathways have significantly progressed the state of the art of ultrafast spectroscopy, as evidenced by numerous examples described in this chapter. All-optical attosecond interferometry is applicable to a wide range of systems, such as atomic and molecular gases and condensed-matter systems. Combining the two pathways has the potential to access to hitherto elusive ultrafast multi-electron and chiral phenomena.

Black-hole powered quantum coherent amplifier

Misra A., Chattopadhyay P., Svidzinsky A., Scully M. O. & Kurizki G. (2024) npj Quantum Information.

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

How synchronized human networks escape local minima

Shniderman E., Avraham Y., Shahal S., Duadi H., Davidson N. & Fridman M. (2024) Nature Communications.

Finding the global minimum in complex networks while avoiding local minima is challenging in many types of networks. In human networks and communities, adapting and finding new stable states amid changing conditions due to conflicts, climate changes, or disasters, is crucial. We studied the dynamics of complex networks of violin players and observed that such human networks have different methods to avoid local minima than other non-human 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.

Recovering Quantum Coherence of a Cavity Qubit Coupled to a Noisy Ancilla through Real-Time Feedback

Goldblatt U., Kahn N., Hazanov S., Milul O., Guttel B., Joshi L. M., Chausovsky D., Lafont F. & Rosenblum S. (2024) Physical Review X.

Decoherence in qubits, caused by their interaction with a noisy environment, poses a significant challenge to the development of reliable quantum processors. A prominent source of errors arises from noise in coupled ancillas, which can quickly spread to qubits. By actively monitoring these noisy ancillas, it is possible to not only identify qubit decoherence events but also to correct these errors in real time. This approach is particularly beneficial for bosonic qubits, where the interaction with ancillas is a dominant source of decoherence. In this work, we uncover the intricate dynamics of decoherence in a superconducting cavity qubit due to its interaction with a noisy transmon ancilla. By tracking the noisy ancilla trajectory and using real-time feedback, we successfully recover the lost coherence of the cavity qubit, achieving a fivefold increase in its pure dephasing time. Additionally, by detecting ancilla errors and converting them into erasures, we improve the pure dephasing time by more than an order of magnitude. These advances are essential for realizing long-lived cavity qubits with high-fidelity gates, and they pave the way for more efficient bosonic quantum error-correction codes.

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

Petrosyan D., Fortágh J. & Kurizki G. (2024) EPJ Quantum Technology.

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

Scalable Architecture for Trapped-Ion Quantum Computing Using rf Traps and Dynamic Optical Potentials

Schwerdt D., Peleg L., Shapira Y., Priel N., Florshaim Y., Gross A., Zalic A., Afek G., Akerman N., Stern A., Kish A. B. & Ozeri R. (2024) Physical Review X.

Qubits based on ions trapped in linear radio-frequency traps form a successful platform for quantum computing, due to their high fidelity of operations, all-to-all connectivity, and degree of local control. In principle, there is no fundamental limit to the number of ion-based qubits that can be confined in a single 1D register. However, in practice, there are two main issues associated with long trapped-ion crystals, that stem from the "softening"of their modes of motion, upon scaling up: high heating rates of the ions' motion and a dense motional spectrum; both impede the performance of high-fidelity qubit operations. Here, we propose a holistic, scalable architecture for quantum computing with large ion crystals that overcomes these issues. Our method relies on dynamically operated optical potentials that instantaneously segment the ion crystal into cells of a manageable size. We show that these cells behave as nearly independent quantum registers, allowing for parallel entangling gates on all cells. The ability to reconfigure the optical potentials guarantees connectivity across the full ion crystal and also enables efficient midcircuit measurements. We study the implementation of large-scale parallel multiqubit entangling gates that operate simultaneously on all cells and present a protocol to compensate for crosstalk errors, enabling full-scale usage of an extensively large register. We illustrate that this architecture is advantageous both for fault-tolerant digital quantum computation and for analog quantum simulations.

Scalable Architecture for Trapped-Ion Quantum Computing Using rf Traps and Dynamic Optical Potentials

Schwerdt D., Peleg L., Shapira Y., Priel N., Florshaim Y., Gross A., Zalic A., Afek G., Akerman N., Stern A., Kish A. B. & Ozeri R. (2024) Physical Review X.

Qubits based on ions trapped in linear radio-frequency traps form a successful platform for quantum computing, due to their high fidelity of operations, all-to-all connectivity, and degree of local control. In principle, there is no fundamental limit to the number of ion-based qubits that can be confined in a single 1D register. However, in practice, there are two main issues associated with long trapped-ion crystals, that stem from the "softening"of their modes of motion, upon scaling up: high heating rates of the ions' motion and a dense motional spectrum; both impede the performance of high-fidelity qubit operations. Here, we propose a holistic, scalable architecture for quantum computing with large ion crystals that overcomes these issues. Our method relies on dynamically operated optical potentials that instantaneously segment the ion crystal into cells of a manageable size. We show that these cells behave as nearly independent quantum registers, allowing for parallel entangling gates on all cells. The ability to reconfigure the optical potentials guarantees connectivity across the full ion crystal and also enables efficient midcircuit measurements. We study the implementation of large-scale parallel multiqubit entangling gates that operate simultaneously on all cells and present a protocol to compensate for crosstalk errors, enabling full-scale usage of an extensively large register. We illustrate that this architecture is advantageous both for fault-tolerant digital quantum computation and for analog quantum simulations.

How Single-Photon Switching is Quenched with Multiple Λ -Level Atoms

Poddubny A. N., Rosenblum S. & Dayan B. (2024) Physical Review Letters.

Single-photon nonlinearity, namely, the change in the response of the system as the result of the interaction with a single photon, is generally considered an inherent property of a single quantum emitter. Although the dependence on the number of emitters is well understood for the case of two-level systems, deterministic operations such as single-photon switching or photon-atom gates inherently require more complex level structures. Here, we theoretically consider single-photon switching in ensembles of emitters with a Λ-level scheme and show that the switching efficiency vanishes with the number of emitters. Interestingly, the mechanism behind this behavior is the quantum Zeno effect, manifested in a slowdown of the photon-controlled dynamics of the atomic ground states.

How Single-Photon Switching is Quenched with Multiple Λ -Level Atoms

Poddubny A. N., Rosenblum S. & Dayan B. (2024) Physical Review Letters.

Single-photon nonlinearity, namely, the change in the response of the system as the result of the interaction with a single photon, is generally considered an inherent property of a single quantum emitter. Although the dependence on the number of emitters is well understood for the case of two-level systems, deterministic operations such as single-photon switching or photon-atom gates inherently require more complex level structures. Here, we theoretically consider single-photon switching in ensembles of emitters with a Λ-level scheme and show that the switching efficiency vanishes with the number of emitters. Interestingly, the mechanism behind this behavior is the quantum Zeno effect, manifested in a slowdown of the photon-controlled dynamics of the atomic ground states.

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

Shen X., Davidson N., Bruun G. M., Sun M. & Wu Z. (2024) Physical review letters.

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

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

Arshad M. J., Bekker C., Haylock B., Skrzypczak K., White D., Griffiths B., Gore J., Morley G. W., Salter P., Smith J., Zohar I., Finkler A., Altmann Y., Gauger E. M. & Bonato C. (2024) Physical Review Applied.

Characterizing the time over which quantum coherence survives is critical for any implementation of quantum bits, memories, and sensors. The usual method for determining a quantum system's decoherence rate involves a suite of experiments probing the entire expected range of this parameter, and extracting the resulting estimation in postprocessing. Here we present an adaptive multiparameter Bayesian approach, based on a simple analytical update rule, to estimate the key decoherence timescales (T1, T2∗ - , and T2) and the corresponding decay exponent of a quantum system in real time, using information gained in preceding experiments. This approach reduces the time required to reach a given uncertainty by a factor up to an order of magnitude, depending on the specific experiment, compared to the standard protocol of curve fitting. A further speedup of a factor approximately 2 can be realized by performing our optimization with respect to sensitivity as opposed to variance.

Chaotic scattering in ultracold atom-ion collisions

Pinkas M., Wengrowicz J., Akerman N. & Ozeri R. (2024) arXiv.org.

We report on signatures of classical chaos in ultracold collisions between a trapped ion and a free atom. Using numerical simulations, we show that the scattering dynamics can be highly sensitive to initial conditions for various mass ratios and trapping frequencies, indicating the onset of chaos. We quantify this chaotic dynamics by calculating its fractal dimension. We show that for a trapped 88Sr+ ion and a free 87Rb atom chaotic dynamic appears under experimentally relevant conditions, and find its characteristic energy scale. The observation of classical chaos in atom-trapped-ion collisions suggests that signatures of quantum chaos might appear, for example, through a Wigner-Dyson distribution of collisional resonances.

Chaotic scattering in ultracold atom-ion collisions

Pinkas M., Wengrowicz J., Akerman N. & Ozeri R. (2024) arXiv.org.

We report on signatures of classical chaos in ultracold collisions between a trapped ion and a free atom. Using numerical simulations, we show that the scattering dynamics can be highly sensitive to initial conditions for various mass ratios and trapping frequencies, indicating the onset of chaos. We quantify this chaotic dynamics by calculating its fractal dimension. We show that for a trapped 88Sr+ ion and a free 87Rb atom chaotic dynamic appears under experimentally relevant conditions, and find its characteristic energy scale. The observation of classical chaos in atom-trapped-ion collisions suggests that signatures of quantum chaos might appear, for example, through a Wigner-Dyson distribution of collisional resonances.

Sensing microscopic noise events by frequent quantum measurements

Virzì S., Knoll L. T., Avella A., Piacentini F., Gherardini S., Gramegna M., Kurizki G., Kofman A. G., Degiovanni I. P., Genovese M. & Caruso F. (2024) Physical Review Applied.

We propose and experimentally demonstrate a general method allowing us to unravel microscopic noise events that affect a continuous quantum variable. Such unraveling is achieved by frequent measurements of a discrete variable coupled to the continuous one. The experimental realization involves photons traversing a noisy channel. There, their polarization, whose coupling to the photons' spatial wave packet is subjected to stochastic noise, is frequently measured in the quantum Zeno regime. The measurements not only preserve the polarization state, but also enable the recording of the full noise statistics from the spatially resolved detection of the photons emerging from the channel. This method proves the possibility of employing photons as quantum noise sensors and robust carriers of information.

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

Liberman A., Lahaye R., Smartsev S., Tata S., Benracassa S., Golovanov A., Levine E., Thaury C. & Malka V. (2024) Optics Letters.

This paper presents the first experimental realization of a scheme that allows for the tuning of the velocity of peak intensity of a focal spot with relativistic intensity. By combining a tunable pulse-front curvature with the axial intensity deposition characteristics of an axiparabola, an aspheric optical element, this system provides control over the dynamics of laser-wakefield accelerators. We demonstrate the ability to modify the velocity of peak intensity of ultrashort laser pulses to be superluminal or subluminal. The experimental results are supported by theoretical calculations and simulations, strengthening the case for the axiparabola as a pertinent strategy to achieve more efficient acceleration.

Supersensitive phase estimation by thermal light in a Kerr-nonlinear interferometric setup

Meher N., Poem E., Opatrný T., Firstenberg O. & Kurizki G. (2024) Physical Review A.

Estimation of the phase delay between interferometer arms is the core of transmission phase microscopy. Such phase estimation may exhibit an error below the standard quantum (shot-noise) limit, if the input is an entangled two-mode state, e.g., a N00N state. We show, by contrast, that such supersensitive phase estimation (SSPE) is achievable by incoherent, e.g., thermal, light that is injected into a Mach-Zehnder interferometer via a Kerr-nonlinear two-mode coupler. Phase error is shown to be reduced below 1/n¯, n¯ being the mean photon number, by thermal input in such interferometric setups, even for small nonlinear phase shifts per photon pair or for significant photon loss. Remarkably, the phase accuracy achievable in such setups by thermal input surpasses that of coherent light with the same n¯. Available mode couplers with giant Kerr nonlinearity that stem either from dipole-dipole interactions of Rydberg polaritons in a cold atomic gas, or from cavity-enhanced dispersive atom-field interactions, may exploit such effects to substantially advance interferometric phase microscopy using incoherent, faint light sources.

Supersensitive phase estimation by thermal light in a Kerr-nonlinear interferometric setup

Meher N., Poem E., Opatrný T., Firstenberg O. & Kurizki G. (2024) Physical Review A.

Estimation of the phase delay between interferometer arms is the core of transmission phase microscopy. Such phase estimation may exhibit an error below the standard quantum (shot-noise) limit, if the input is an entangled two-mode state, e.g., a N00N state. We show, by contrast, that such supersensitive phase estimation (SSPE) is achievable by incoherent, e.g., thermal, light that is injected into a Mach-Zehnder interferometer via a Kerr-nonlinear two-mode coupler. Phase error is shown to be reduced below 1/n¯, n¯ being the mean photon number, by thermal input in such interferometric setups, even for small nonlinear phase shifts per photon pair or for significant photon loss. Remarkably, the phase accuracy achievable in such setups by thermal input surpasses that of coherent light with the same n¯. Available mode couplers with giant Kerr nonlinearity that stem either from dipole-dipole interactions of Rydberg polaritons in a cold atomic gas, or from cavity-enhanced dispersive atom-field interactions, may exploit such effects to substantially advance interferometric phase microscopy using incoherent, faint light sources.

Temporal quantum eraser: Fusion gates with distinguishable photons

Aqua Z. & Dayan B. (2024) Physical Review A.

Linear-optics gates, the enabling tool of photonic quantum information processing, depend on indistinguishable photons, as they harness quantum interference to achieve nonlinear operations. Traditionally, meeting this criterion involves generating pure identical photons, a task that remains a significant challenge in the field. Yet, the required indistinguishability is linked to the spatial exchange symmetry of the multiphoton wave function and does not strictly necessitate identical photons. Here, we show that the ideal operation of two-photon gates, particularly fusion gates, can be recovered from distinguishable photons by ensuring the exchange symmetry of the input photonic state. To this end, we introduce a temporal quantum eraser between a pair of modally impure single-photon sources, which heralds the symmetry of the generated two-photon state. We demonstrate this mechanism in two relevant platforms: parametric photon pair generation and single-photon extraction by a single quantum emitter. The ability to lift the requirement for identical photons bears considerable potential in linear-optics quantum information processing.

Laser Proton Acceleration from a Near-Critical Imploding Gas Target

Seemann O., Wan Y., Tata S., Kroupp E. & Malka V. (2024) Physical Review Letters.

The interaction between relativistic intense laser pulses and near-critical-density targets has been sought after in order to increase the efficiency of laser-plasma energy coupling, particularly for laser-driven proton acceleration. To achieve the density regime for high-repetition-rate applications, one elusive approach is to use gas targets, provided that stringent target density profile requirements are met. These include reaching the critical plasma density while maintaining micron-scale density gradients. In this Letter, we present a novel scheme for achieving the necessary requirements using optical laser pulses to transversely shape the target and create a colliding shock wave in both planar and cylindrical geometries. Utilizing this approach, we experimentally demonstrated stable proton acceleration and achieved up to 5 MeV in a monoenergetic distribution and particle numbers above 108 Sr-1 MeV-1 using a 1.5 J energy on-target laser pulse. The Letter also reports for the first time an extend series of 200 consecutive shots that demonstrates the robustness of the approach and its maturity for applications. These results open the door for future work in controlling gas targets and optimizing the acceleration process for more energetic multipetawatt laser systems.

Attosecond transient interferometry

Kneller O., Mor C., Klimkin N. D., Yaffe N., Krüger M., Azoury D., Uzan-Narovlansky A. J., Federman Y., Rajak D., Bruner B. D., Smirnova O., Patchkovskii S., Mairesse Y., Ivanov M. & Dudovich N. (2024) Nature Photonics.

Attosecond transient absorption resolves the instantaneous response of a quantum system as it interacts with a laser field, by mapping its sub-cycle dynamics onto the absorption spectrum of attosecond pulses. However, the quantum dynamics are imprinted in the amplitude, phase and polarization state of the attosecond pulses. Here we introduce attosecond transient interferometry and measure the transient phase, as we follow its evolution within the optical cycle. We demonstrate how such phase information enables us to decouple the multiple quantum paths induced in a light-driven system, isolating their coherent contribution and retrieving their temporal evolution. Applying attosecond transient interferometry reveals the Stark shift dynamics in helium and retrieves long-term electronic coherences in neon. Finally, we present a vectorial generalization of our scheme, theoretically demonstrating the ability to isolate the underlying anomalous current in light-driven topological materials. Our scheme provides a direct insight into the interplay of light-induced dynamics and topology. Attosecond transient interferometry holds the potential to considerably extend the scope of attosecond metrology, revealing the underlying coherences in light-driven complex systems.

Roadmap on nanoscale magnetic resonance imaging

Budakian R., Finkler A., Eichler A., Poggio M., Degen C. L., Tabatabaei S., Lee I., Hammel P. C., Eugene S. P., Taminiau T. H., Walsworth R. L., London P., Bleszynski Jayich A., Ajoy A., Pillai A., Wrachtrup J., Jelezko F., Bae Y., Heinrich A. J., Ast C. R., Bertet P., Cappellaro P., Bonato C., Altmann Y. & Gauger E. (2024) Nanotechnology.

The field of nanoscale magnetic resonance imaging (NanoMRI) was started 30 years ago. It was motivated by the desire to image single molecules and molecular assemblies, such as proteins and virus particles, with near-atomic spatial resolution and on a length scale of 100 nm. Over the years, the NanoMRI field has also expanded to include the goal of useful high-resolution nuclear magnetic resonance (NMR) spectroscopy of molecules under ambient conditions, including samples up to the micron-scale. The realization of these goals requires the development of spin detection techniques that are many orders of magnitude more sensitive than conventional NMR and MRI, capable of detecting and controlling nanoscale ensembles of spins. Over the years, a number of different technical approaches to NanoMRI have emerged, each possessing a distinct set of capabilities for basic and applied areas of science. The goal of this roadmap article is to report the current state of the art in NanoMRI technologies, outline the areas where they are poised to have impact, identify the challenges that lie ahead, and propose methods to meet these challenges. This roadmap also shows how developments in NanoMRI techniques can lead to breakthroughs in emerging quantum science and technology applications.

Inertial geometric quantum logic gates

Turyansky D., Ovdat O., Dann R., Aqua Z., Kosloff R., Dayan B. & Pick A. (2024) Physical Review Applied.

We present rapid and robust protocols for stimulated rapid adiabatic passage and quantum logic gates. Our gates are based on geometric phases acquired by instantaneous eigenstates of a slowly accelerating "inertial"Hamiltonian. To begin, we establish the criteria for inertial evolution and subsequently engineer pulse shapes that fulfill these conditions. These tailored pulses are then used to optimize geometric logic gates. We analyze a realization of our protocols with 87Rb atoms, resulting in gate fidelity that approaches the current state of the art, with marked improvements in robustness.

Inverse Mpemba Effect Demonstrated on a Single Trapped Ion Qubit

Aharony Shapira S., Shapira Y., Markov J., Teza G., Akerman N., Raz O. & Ozeri R. (2024) Physical Review Letters.

The Mpemba effect is a counterintuitive phenomena in which a hot system reaches a cold temperature faster than a colder system, under otherwise identical conditions. Here, we propose a quantum analog of the Mpemba effect, on the simplest quantum system, a qubit. Specifically, we show it exhibits an inverse effect, in which a cold qubit reaches a hot temperature faster than a hot qubit. Furthermore, in our system a cold qubit can heat up exponentially faster, manifesting the strong version of the effect. This occurs only for sufficiently coherent systems, making this effect quantum mechanical, i.e., due to interference effects. We experimentally demonstrate our findings on a single 88Sr+ trapped ion qubit. The existence of this anomalous relaxation effect in simple quantum systems reveals its fundamentality, and may have a role in designing and operating quantum information processing devices.

Inverse Mpemba Effect Demonstrated on a Single Trapped Ion Qubit

Aharony Shapira S., Shapira Y., Markov J., Teza G., Akerman N., Raz O. & Ozeri R. (2024) Physical Review Letters.

The Mpemba effect is a counterintuitive phenomena in which a hot system reaches a cold temperature faster than a colder system, under otherwise identical conditions. Here, we propose a quantum analog of the Mpemba effect, on the simplest quantum system, a qubit. Specifically, we show it exhibits an inverse effect, in which a cold qubit reaches a hot temperature faster than a hot qubit. Furthermore, in our system a cold qubit can heat up exponentially faster, manifesting the strong version of the effect. This occurs only for sufficiently coherent systems, making this effect quantum mechanical, i.e., due to interference effects. We experimentally demonstrate our findings on a single 88Sr+ trapped ion qubit. The existence of this anomalous relaxation effect in simple quantum systems reveals its fundamentality, and may have a role in designing and operating quantum information processing devices.

Laser-Induced Electron Diffraction in Chiral Molecules

Rajak D., Beauvarlet S., Kneller O., Comby A., Cireasa R., Descamps D., Fabre B., Gorfinkiel J. D., Higuet J., Petit S., Rozen S., Ruf H., Thiré N., Blanchet V., Dudovich N., Pons B. & Mairesse Y. (2024) Physical Review X.

Strong laser pulses enable probing molecules with their own electrons. The oscillating electric field tears electrons off a molecule, accelerates them, and drives them back toward their parent ion within a few femtoseconds. The electrons are then diffracted by the molecular potential, encoding its structure and dynamics with angstrom and attosecond resolutions. Using elliptically polarized laser pulses, we show that laser-induced electron diffraction is sensitive to the chirality of the target. The field selectively ionizes molecules of a given orientation and drives the electrons along different sets of trajectories, leading them to recollide from different directions. Depending on the handedness of the molecule, the electrons are preferentially diffracted forward or backward along the light propagation axis. This asymmetry, reaching several percent, can be reversed for electrons recolliding from two ends of the molecule. The chiral sensitivity of laser-induced electron diffraction opens a new path to resolve ultrafast chiral dynamics.

Real-time visualization of the laser-plasma wakefield dynamics

Wan Y., Tata S., Seemann O., Levine E. Y., Kroupp E. & Malka V. (2024) Science advances.

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

Efficient laser wakefield accelerator in pump depletion dominated bubble regime

Horný V., Bleotu P. G., Ursescu D., Malka V. & Tomassini P. (2024) Physical Review E.

With the usage of the postcompression technique, few-cycle joule-class laser pulses are nowadays available extending the state of the art of 100 TW-class laser working at 10 Hz repetition. In this Letter, we explore the potential of wakefield acceleration when driven with such pulses. The numerical modeling predicts that 50% of the laser pulse energy can be transferred into electrons with energy above 15 MeV, and with charge exceeding several nanocoulombs for the electrons at hundreds of MeV energy. In such a regime, the laser pulse depletes its energy to plasma rapidly driving a strong cavitated wakefield. The self-steepening effect induces a continuous prolongation of a bubble resulting in a massive continuous self-injection that explains the extremely high charge of the beam rending this approach suitable for promoting Bremsstrahlung emitter and generator of tertiary particles, including neutrons released through photonuclear reactions.

Electronic-Resonance Coherent Anti-Stokes Raman Scattering Spectroscopy and Microscopy

Tang Q., Li B., Wang J., Liu Y., Pinkas I., Rigneault H., Oron D. & Ren L. (2024) ACS Photonics.

Advanced optical microscopy techniques, such as fluorescence and vibrational imaging, play a key role in science and technology. Both the sensitivity and the chemical selectivity are important for applications of these methods in biomedical research. However, there are few bioimaging techniques that could offer vibrational sensitivity and selectivity simultaneously. Here, we demonstrate electronic-resonance coherent anti-Stokes Raman scattering (ER-CARS) spectroscopy and microscopy with high sensitivity and high selectivity by using lock-in detection. With this ER-CARS strategy, we observed the low-wavenumber Raman spectra of various infrared dyes in solution at ultralow vibrational frequencies (from ∼20 to 330 cm-1) using a sharp edge filter and impulsive CARS excitation at low input power. We demonstrate low-frequency ER-CARS imaging of cells stained with infrared dyes using only 200 mW of input power, fundamentally mitigating photobleaching issues. We also show the application of ER-CARS in the detection of nonfluorescent molecules. Finally, we demonstrate the chemically selective capabilities of ER-CARS microscopy by imaging tissues stained with two different infrared dyes. These ER-CARS spectroscopy and microscopy results pave the way toward ultrasensitive Raman imaging of biological systems and present a pathway toward highly multiplexed selective imaging.

Design and fabrication of ultrahigh Q chip-based silica WGM micro-resonators for single-atom cavity-QED

Ohana T. S., Guendelman G., Mishuk E., Kandel N., Garti D., Gurovich D., Bitton O. & Dayan B. (2024) Optics Express.

Of the many applications of whispering-gallery-mode (WGM) micro-resonators, single-atom cavity quantum electrodynamics (cavity-QED) poses the most extreme demands on mode volume, dimensions, and quality factor (Q). Here we present the procedure for the fabrication of chip-based, small mode-volume, ultrahigh-Q silica WGM micro-resonators, designed for single-emitter cavity-QED. We demonstrate micro-resonators at varying geometries, from toroidal to micro-spheres, yielding ultrahigh-qualities as high as 1.7 × 108 at 780nm. We present a comprehensive theoretical model that allows tailoring the fabrication process to attain the desired micro-resonator geometry.

Organic Crystals and Optical Functions in Biology: Knowns and Unknowns

Addadi L., Kronik L., Leiserowitz L., Oron D. & Weiner S. (2024) Advanced Materials.

Organic crystals are widely used by animals to manipulate light for producing structural colors and for improving vision. To date only seven crystal types are known to be used, and among them β-guanine crystals are by far the most widespread. The fact that almost all these crystals have unusually high refractive indices (RIs) is consistent with their light manipulation function. Here, the physical, structural, and optical principles of how light interacts with the polarizable free-electron-rich environment of these quasiaromatic molecules are addressed. How the organization of these molecules into crystalline arrays introduces optical anisotropy and finally how organisms control crystal morphology and superstructural organization to optimize functions in light reflection and scattering are also discussed. Many open questions remain in this fascinating field, some of which arise out of this in-depth analysis of the interaction of light with crystal arrays. More types of organic crystals will probably be discovered, as well as other organisms that use these crystals to manipulate light. The insights gained from biological systems can also be harnessed for improving synthetic light-manipulating materials.

Synchronization in Coupled Laser Arrays with Correlated and Uncorrelated Disorder

Pando A., Gadasi S., Bernstein E., Stroev N., Friesem A. & Davidson N. (2024) Physical Review Letters.

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 nontrivial effect on the decrease of phase synchronization, which depends on the ratio of the disorder correlation length over the average number of synchronized lasers. The experimental results are supported by numerical simulations and analytic derivations.

Synchronization in Coupled Laser Arrays with Correlated and Uncorrelated Disorder

Pando A., Gadasi S., Bernstein E., Stroev N., Friesem A. & Davidson N. (2024) Physical Review Letters.

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 nontrivial effect on the decrease of phase synchronization, which depends on the ratio of the disorder correlation length over the average number of synchronized lasers. The experimental results are supported by numerical simulations and analytic derivations.

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 1, the notion of the Berry phase has permeated all branches of physics and plays an important part in a variety of quantum phenomena 2. 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.

Efficient coupling of light to an atomic tweezer array in a cavity

Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2024) Physical Review Research.

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 how a moderate-finesse cavity can overcome 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.

Efficient coupling of light to an atomic tweezer array in a cavity

Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2024) Physical Review Research.

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 how a moderate-finesse cavity can overcome 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.

Efficient coupling of light to an atomic tweezer array in a cavity

Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2024) Physical Review Research.

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 how a moderate-finesse cavity can overcome 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.

Thermodynamic sensing of quantum nonlinear noise correlations

Meher N., Opatrný T. & Kurizki G. (2024) Quantum Science and Technology.

We put forth the concept of quantum noise sensing in nonlinear two-mode interferometers coupled to mechanical oscillators. These autonomous machines are capable of sensing quantum nonlinear correlations of two-mode noisy fields via their thermodynamic variable of extractable work, alias work capacity (WC) or ergotropy. The fields are formed by thermal noise input via its interaction with multi-level systems inside the interferometer. Such interactions amount to the generation of two-mode quantum nonlinear gauge fields that may be partly unknown. We show that by monitoring a mechanical oscillator coupled to the interferometer, one can sense the WC of one of the output field modes and thereby reveal the quantum nonlinear correlations of the field. The proposed quantum sensing method can provide an alternative to quantum multiport interferometry where the output field is unraveled by tomography. This method may advance the simulation and control of multimode quantum nonlinear gauge fields.

Benchmarking the optimization of optical machines with the planted solutions

Stroev N., Berloff N. G. & Davidson N. (2024) Communications Physics.

This research focuses on developing effective benchmarks for quadratic unconstrained binary optimization instances, crucial for evaluating the performance of Ising hardware and solvers. Currently, the field lacks accessible and reproducible models for systematically testing such systems, particularly in terms of detailed phase space characterization. Here, we introduce universal generative models based on an extension of Hebbs rule of associative memory with asymmetric pattern weights. We conduct comprehensive calculations across different scales and dynamical equations, examining outcomes like the probabilities of reaching the ground state, planted state, spurious state, or other energy levels. Additionally, the generated problems reveal properties such as the easy-hard-easy complexity transition and complex solution cluster structures. This method offers a promising platform for analyzing and understanding the behavior of physical hardware and its simulations, contributing to future advancements in optimization technologies.

Dissipative transfer of quantum correlations from light to atomic arrays

Ben-Maimon R., Solomons Y. & Shahmoon E. (2024) Physical Review A.

We show how the directional collective response of atomic arrays to light can be exploited for the dissipative generation of entangled atomic states, relevant for, e.g., quantum metrology. We consider an atomic array illuminated by a paraxial beam of a squeezed-vacuum field and demonstrate that quantum-squeezing correlations are dissipatively transferred to the array atoms, resulting in an atomic spin-squeezed steady state. We find that the entanglement transfer efficiency and hence the degree of spin squeezing are determined by the resonant optical reflectivity of the array. Considering realistic cases of finite-size array and illuminating beam, we find how the spin-squeezing strength scales with system parameters, such as the number of layers in the array and its spatial overlap with the beam. We discuss applications in atomic clocks in both optical and microwave domains.

Frequency Dissemination with Less than 2 × 10-18Fractional-Frequency Instability Over 120 km of a Commercial Fiber Infrastructure

Alon M., Akerman N., Shafir E. & Ozeri R. (2024) .

This work presents frequency dissemination with fractional-frequency instability of 2× 10-18 at a 100-second interrogation time on a single-mode fiber communication infrastructure, the system consisted of a Michelson interferometer over 120 km of optical fiber connecting the Weizmann Institute of Science and Tel Aviv University. We used optical add-drop multiplexers to incorporate the Michelson interferometer into an active communication infrastructure and used it to detect the phase noise accumulated on the fiber channel. A phase-locked loop controlling an acoustic optic modulator was used to correct it. This facilitated distributing a phase-stable frequency at the remote station.

Frequency Dissemination with Less than 2 × 10-18Fractional-Frequency Instability Over 120 km of a Commercial Fiber Infrastructure

Alon M., Akerman N., Shafir E. & Ozeri R. (2024) .

This work presents frequency dissemination with fractional-frequency instability of 2× 10-18 at a 100-second interrogation time on a single-mode fiber communication infrastructure, the system consisted of a Michelson interferometer over 120 km of optical fiber connecting the Weizmann Institute of Science and Tel Aviv University. We used optical add-drop multiplexers to incorporate the Michelson interferometer into an active communication infrastructure and used it to detect the phase noise accumulated on the fiber channel. A phase-locked loop controlling an acoustic optic modulator was used to correct it. This facilitated distributing a phase-stable frequency at the remote station.

Photon Number Splitting Attack Proposal and Analysis of an Experimental Scheme

Ashkenazy A., Idan Y., Korn D., Fixler D., Dayan B. & Cohen E. (2024) Advanced Quantum Technologies.

Photon-number-splitting (PNS) is a well-known theoretical attack on quantum key distribution (QKD) protocols that employ weak coherent states produced by attenuated laser pulses. However, beyond the fact that it has not yet been demonstrated experimentally, its plausibility and effect on quantum bit error rate are questioned. In this work, an experimental scheme is presented for PNS attack employing demonstrated technological capabilities, specifically a single-photon Raman interaction (SPRINT) in a cavity-enhanced three-level atomic system. Several aspects of the proposed implementation are addressed, analytically and simulatively, and the eavesdropper's information gain by the attack is calculated. Furthermore, it is analytically shown that the scheme results in a small (yet non-zero) quantum bit error rate, and a comparison to purely theoretical analyses in the literature is presented. It is believed that the inherent nonlinearity of the PNS attack unavoidably affects the optical modes sent to the receiver, and accordingly will always result in some error rate.

A Redox-Active Ionic Liquid Surface Treatment for Healing CsPbBr3 Nanocrystals

Crans K. D., Cohen H., Nehoray A. A., Oron D., Kazes M. & Brutchey R. L. (2024) Nano Letters.

Additive engineering of lead halide perovskites has been a successful strategy for reducing a variety of deleterious defect types. Ionic liquids (ILs) are a unique group of such additives that have been used to passivate halide vacancies in both bulk lead halide perovskites and their colloidal nanocrystal analogues. Herein, we expand the types of defects that can be addressed through IL treatments in CsPbBr3 nanocrystals with a novel phosphonium tribromide IL that heals metallic lead surface defects through redox chemistry. This new type of surface treatment leads to a significant increase in PLQY and outperforms equivalent treatments with non-redox-active bromide ILs. Such redox-active ligands widen the scope of defect types that can be addressed in semiconductor nanocrystals.

Coherent dynamics of a nuclear-spin-isomer superposition

Levin T. & Meir Z. (2024) arXiv.org.

Preserving quantum coherence with the increase of a system's size and complexity is a major challenge. Molecules, with their diverse sizes and complexities and many degrees of freedom, are an excellent platform for studying the transition from quantum to classical behavior. While most quantum-control studies of molecules focus on vibrations and rotations, we focus here on creating a quantum superposition between two nuclear-spin isomers of the same molecule. We present a scheme that exploits an avoided crossing in the spectrum to create strong coupling between two uncoupled nuclear-spin-isomer states, hence creating an isomeric qubit. We model our scheme using a four-level Hamiltonian and explore the coherent dynamics in the different regimes and parameters of our system. Our four-level model and approach can be applied to other systems with a similar energy-level structure.

Bio-Inspired Crystalline Core-Shell Guanine Spherulites

Alus L., Houben L., Shaked N., Niazov-Elkan A., Pinkas I., Oron D. & Addadi L. (2024) Advanced Materials.

Spherical particles with diameters within the wavelength of visible light, known as spherulites, manipulate light uniquely due to their spatial organization and their structural birefringence. Most of the known crystalline spherulites are branched, and composed of metals, alloys, and semi-crystalline polymers. Recently, a different spherulite architecture is discovered in the vision systems of decapod crustaceans - core-shell spherulites composed of highly birefringent ((Formula presented.)) organic single-crystal platelets, with exceptional optical properties. These metastructures, which efficiently scatter light even in dense aqueous environments, have no synthetic equivalence and serve as a natural proof-of-concept as well as synthetic inspiration for thin scattering media. Here, the synthesis of core-shell spherulites composed of guanine crystal platelets (((Formula presented.)) is presented in a two-step emulsification process in which a water/oil/water emulsion and induced pH changes are used to promote interfacial crystallization. Carboxylic acids neutralize the dissolved guanine salts to form spherulites composed of single, radially stacked, β-guanine platelets, which are oriented tangentially to the spherulite surface. Using Mie theory calculations and forward scattering measurements from single spherulites, it is found that due to the single-crystal properties and orientation, the synthetic spherulites possess a high tangential refractive index, similarly to biogenic particles.

Observation of Three-Photon Cascaded Emission from Triexcitons in Giant CsPbBr3 Quantum Dots at Room Temperature

Kazes M., Nakar D., Cherniukh I., Bodnarchuk M. I., Feld L. G., Zhu C., Amgar D., Rainò G., Kovalenko M. V. & Oron D. (2024) Nano Letters.

Colloidal semiconductor nanocrystals have long been considered a promising source of time-correlated and entangled photons via the cascaded emission of multiexcitonic states. The spectroscopy of such cascaded emission, however, is hindered by efficient nonradiative Auger-Meitner decay, rendering multiexcitonic states nonemissive. Here we present room-temperature heralded spectroscopy of three-photon cascades from triexcitons in giant CsPbBr3 nanocrystals. We show that this system exhibits second- and third-order correlation function values, g(2)(0) and g(3)(0,0), close to unity, identifying very weak binding of both biexcitons and triexcitons. Combining fluorescence lifetime analysis, photon statistics, and spectroscopy, we can readily identify emission from higher multiexcitonic states. We use this to verify emission from a single emitter despite high emission quantum yields of multiply excited states and comparable emission lifetimes of singly and multiply excited states. Finally, we present potential pathways toward control of the photon number statistics of multiexcitonic emission cascades.

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

Xu L., Tutunnikov I., Prior Y. & Averbukh I. (2024) Physical Review Research.

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

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

Xu L., Tutunnikov I., Prior Y. & Averbukh I. (2024) Physical Review Research.

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

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

Xu L., Tutunnikov I., Prior Y. & Averbukh I. (2024) Physical Review Research.

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

Guided Search to Self-Healing in Semiconductors

Py-Renaudie A., Soffer Y., Singh P., Kumar S., Ceratti D. R., Mualem Y., Rosenhek-Goldian I., Oron D., Cohen S. R., Schulz P., Cahen D. & Guillemoles J. F. (2023) Advanced Functional Materials.

Self-healing (SH) of (opto)electronic material damage can have a huge impact on resource sustainability. The rising interest in halide perovskite (HaP) compounds over the past decade is due to their excellent semiconducting properties for crystals and films, even if made by low-temperature solution-based processing. Direct proof of self-healing in Pb-based HaPs is demonstrated through photoluminescence recovery from photodamage, fracture healing and their use as high-energy radiation and particle detectors. Here, the question of how to find additional semiconducting materials exhibiting SH, in particular lead-free ones is addressed. Applying a data-mining approach to identify semiconductors with favorable mechanical and thermal properties, for which Pb HaPs are clear outliers, it is found that the Cs2AuIAuIIIX6, (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.

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.

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 × 10−5 noise photons per pulse, and a 1/e lifetime of 108 ns. This combination of performances is a record for continuous-readout memories.

A new spin on impact ionization

Kazes M. & Oron D. (2023) Nature Materials.

Quantum dots are engineered to use dopant states to achieve substantially enhanced impact ionization, which is potentially useful for light-harvesting applications.

Room Temperature Relaxometry of Single Nitrogen Vacancy Centers in Proximity to α-RuCl3 Nanoflakes

Kumar J., Yudilevich D., Smooha A., Zohar I., Pariari A. K., Stöhr R., Denisenko A., Hücker M. & Finkler A. (2023) Nano Letters.

Nitrogen vacancy (NV) center-based magnetometry has been proven to be a versatile sensor for various classes of magnetic materials in broad temperature and frequency ranges. Here, we use the longitudinal relaxation time T1 of single NV centers to investigate the spin dynamics of nanometer-thin flakes of α-RuCl3 at room temperature. We observe a significant reduction in the T1 in the presence of α-RuCl3 in the proximity of NVs, which we attribute to paramagnetic spin noise confined in the 2D hexagonal planes. Furthermore, the T1 time exhibits a monotonic increase with an applied magnetic field. We associate this trend with the alteration of the spin and charge noise in α-RuCl3 under an external magnetic field. These findings suggest that the influence of the spin dynamics of α-RuCl3 on the T1 of the NV center can be used to gain information about the material itself and the technique to be used on other 2D materials.

Excitation Intensity-Dependent Quantum Yield of Semiconductor Nanocrystals

Ghosh S., Ross U., Chizhik A. M., Kuo Y., Jeong B. G., Bae W. K., Park K., Li J., Oron D., Weiss S., Enderlein J. & Chizhik A. I. (2023) Journal of Physical Chemistry Letters.

One of the key phenomena that determine the fluorescence of nanocrystals is the nonradiative Auger-Meitner recombination of excitons. This nonradiative rate affects the nanocrystals fluorescence intensity, excited state lifetime, and quantum yield. Whereas most of the above properties can be directly measured, the quantum yield is the most difficult to assess. Here we place semiconductor nanocrystals inside a tunable plasmonic nanocavity with subwavelength spacing and modulate their radiative de-excitation rate by changing the cavity size. This allows us to determine absolute values of their fluorescence quantum yield under specific excitation conditions. Moreover, as expected considering the enhanced Auger-Meitner rate for higher multiple excited states, increasing the excitation rate reduces the quantum yield of the nanocrystals.

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

Amgar D., Lubin G., Yang G., Rabouw F. T. & Oron D. (2023) Nano Letters.

Semiconductor nanocrystal emission polarization is a crucial probe of nanocrystal physics and an essential factor for nanocrystal-based technologies. While the transition dipole moment for the lowest excited state to ground state transition is well characterized, the dipole moment of higher multiexcitonic transitions is inaccessible via most spectroscopy techniques. Here, we realize direct characterization of the doubly excited-state relaxation transition dipole by heralded defocused imaging. Defocused imaging maps the dipole emission pattern onto a fast single-photon avalanche diode detector array, allowing the postselection of photon pairs emitted from the biexciton-exciton emission cascade and resolving the differences in transition dipole moments. Type-I1/2 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-1. 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 300600 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.

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 spacetime, because the noise is carried by wave propagation. These correlations of wave noise give rise to fluctuation forces such as the Casimir force, they are responsible for the particle creation in the dynamical Casimir effect and in the expanding Universe. This paper considers the noise correlations for light waves in non-exponentially expanding flat space. The paper determines the high-frequency asymptotics of the correlation spectrum in the conformal vacuum. These noise correlations give rise to a nontrivial vacuum energy that may appear as the cosmological constant.

Multichannel waveguide QED with atomic arrays in free space

Solomons Y. & Shahmoon E. (2023) Physical Review A.

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

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

Palaiodimopoulos N. E., Kiefer-Emmanouilidis M., Kurizki G. & Petrosyan D. (2023) SciPost Physics Core.

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

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

Courvoisier A. & Davidson N. (2023) arXiv.org.

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

Spin-strain coupling in nanodiamonds as a unique cluster identifier

Awadallah A., Zohar I. & Finkler A. (2023) Journal of Applied Physics.

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

Advances in device-independent quantum key distribution

Zapatero V., van Leent T., Arnon-Friedman R., Liu W. Z., Zhang Q., Weinfurter H. & Curty M. (2023) npj Quantum Information.

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

Quantum vortices of strongly interacting photons

Drori L., Das B. C., Zohar T. D., Winer G., Poem E., Poddubny A. & Firstenberg O. (2023) Science (New York, N.Y.).

Vortices are topologically nontrivial defects that generally originate from nonlinear field dynamics. All-optical generation of photonic vortices-phase singularities of the electromagnetic field-requires sufficiently strong nonlinearity that is typically achieved in the classical optics regime. We report on the realization of quantum vortices of photons that result from a strong photon-photon interaction in a quantum nonlinear optical medium. The interaction causes faster phase accumulation for copropagating photons, producing a quantum vortex-antivortex pair within the two-photon wave function. For three photons, the formation of vortex lines and a central vortex ring confirms the existence of a genuine three-photon interaction. The wave function topology, governed by two- and three-photon bound states, imposes a conditional phase shift of π per photon, a potential resource for deterministic quantum logic operations.

Improved laser phase locking with intra-cavity adaptive optics

Pando A., Gadasi S., Friesem A. & Davidson N. (2023) Optics Express.

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

Improved laser phase locking with intra-cavity adaptive optics

Pando A., Gadasi S., Friesem A. & Davidson N. (2023) Optics Express.

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

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

Shen X., Davidson N., Bruun G. M., Sun M. & Wu Z. (2023) arXiv.org.

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

Proton acceleration with intense twisted laser light

Willim C., Vieira J., Malka V. & Silva L. O. (2023) Physical Review Research.

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

Nonlinear coherent heat machines

Opatrný T., Bräuer Š., Kofman A. G., Misra A., Meher N., Firstenberg O., Poem E. & Kurizki G. (2023) Science advances.

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

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.

Multi-channel waveguide QED with atomic arrays in free space

Solomons Y. & Shahmoon E. (2023) Physical Review A.

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.

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) .

Single-photon synchronization could prove essential for future quantum optical networks. We demonstrate synchronization of photon pairs with high rate and low noise using a room-temperature atomic quantum memory and compatible single-photon source.

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 ηe2e=25% and final antibunching of gh(2)=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.

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 \u201cbubble\u201d) and surrounded by a thin sheath made of expelled electrons is formed behind the driver. In contrast to the previous theoretical model [W. Lu et al., Phys. Rev. Lett. 96, 165002 (2006)], the presented theory satisfies the energy conservation law, does not require any external fitting parameters, and describes the bubble structure and the electromagnetic field it contains with much higher accuracy in a wide range of parameters. The obtained results are verified by 3D particle-in-cell simulations.

Coupling light to an atomic tweezer array in a cavity

Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2023) arXiv.org.

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

Coupling light to an atomic tweezer array in a cavity

Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2023) arXiv.org.

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

Coupling light to an atomic tweezer array in a cavity

Solomons Y., Shani I., Firstenberg O., Davidson N. & Shahmoon E. (2023) arXiv.org.

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

Interaction of light with matter: A coherent perspective

Tannor D. J. (2023) .

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

Nakav H., Finkelstein R., Peleg L., Akerman N. & Ozeri R. (2023) Physical Review A.

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

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.

Fast design and scaling of multi-qubit gates in large-scale trapped-ion quantum computers

Shapira Y., Peleg L., Schwerdt D., Nemirovsky J., Akerman N., Stern A., Kish A. B. & Ozeri R. (2023) arXiv.org.

Quantum computers based on crystals of electrically trapped ions are a prominent technology for quantum computation. A unique feature of trapped ions is their long-range Coulomb interactions, which come about as an ability to naturally realize large-scale multi-qubit entanglement gates. However, scaling up the number of qubits in these systems, while retaining high-fidelity and high-speed operations is challenging. Specifically, designing multi-qubit entanglement gates in long ion crystals of 100s of ions involves an NP-hard optimization problem, rendering scaling up the number of qubits a conceptual challenge as well. Here we introduce a method that vastly reduces the computational challenge, effectively allowing for a polynomial-time design of fast and programmable entanglement gates, acting on the entire ion crystal. We use this method to investigate the utility, scaling and requirements of such multi-qubit gates. Our method delineates a path towards scaling up quantum computers based on ion-crystals with 100s of qubits.

Fast design and scaling of multi-qubit gates in large-scale trapped-ion quantum computers

Shapira Y., Peleg L., Schwerdt D., Nemirovsky J., Akerman N., Stern A., Kish A. B. & Ozeri R. (2023) arXiv.org.

Quantum computers based on crystals of electrically trapped ions are a prominent technology for quantum computation. A unique feature of trapped ions is their long-range Coulomb interactions, which come about as an ability to naturally realize large-scale multi-qubit entanglement gates. However, scaling up the number of qubits in these systems, while retaining high-fidelity and high-speed operations is challenging. Specifically, designing multi-qubit entanglement gates in long ion crystals of 100s of ions involves an NP-hard optimization problem, rendering scaling up the number of qubits a conceptual challenge as well. Here we introduce a method that vastly reduces the computational challenge, effectively allowing for a polynomial-time design of fast and programmable entanglement gates, acting on the entire ion crystal. We use this method to investigate the utility, scaling and requirements of such multi-qubit gates. Our method delineates a path towards scaling up quantum computers based on ion-crystals with 100s of qubits.

Correlating Fluorescence Intermittency and SecondHarmonic Generation in SingleColloidal 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 atomion 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.

Trap-assisted formation of atomion 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 batterys 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 fields 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 excitonexciton interactions within single nanocrystals. These include weak excitonexciton interactions and their correlation with quantum confinement, biexciton spectral diffusion, multiple biexciton species and biexciton emission polarization.

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

Labat M., Cabadağ J. C., Ghaith A., Irman A., Berlioux A., Berteaud P., Blache F., Bock S., Bouvet F., Briquez F., Chang Y. Y., Corde S., Debus A., De Oliveira C., Duval J. P., Dietrich Y., El Ajjouri M., Eisenmann C., Gautier J., Gebhardt R., Grams S., Helbig U., Herbeaux C., Hubert N., Kitegi C., Kononenko O., Kuntzsch M., LaBerge M., Lê S., Leluan B., Loulergue A., Malka V., Marteau F., Guyen M. H. N., Oumbarek-Espinos D., Pausch R., Pereira D., Püschel T., Ricaud J. P., Rommeluere P., Roussel E., Rousseau P., Schöbel S., Sebdaoui M., Steiniger K., Tavakoli K., Thaury C., Ufer P., Valléau M., Vandenberghe M., Vétéran J., Schramm U. & Couprie M. E. (2023) Nature Photonics.

Free-electron lasers generate high-brilliance coherent radiation at wavelengths spanning from the infrared to the X-ray domains. The recent development of short-wavelength seeded free-electron lasers now allows for unprecedented levels of control on longitudinal coherence, opening new scientific avenues such as ultra-fast dynamics on complex systems and X-ray nonlinear optics. Although those devices rely on state-of-the-art large-scale accelerators, advancements on laser-plasma accelerators, which harness gigavolt-per-centimetre accelerating fields, showcase a promising technology as compact drivers for free-electron lasers. Using such footprint-reduced accelerators, exponential amplification of a shot-noise type of radiation in a self-amplified spontaneous emission configuration was recently achieved. However, employing this compact approach for the delivery of temporally coherent pulses in a controlled manner has remained a major challenge. Here we present the experimental demonstration of a laser-plasma accelerator-driven free-electron laser in a seeded configuration, where control over the radiation wavelength is accomplished. Furthermore, the appearance of interference fringes, resulting from the interaction between the phase-locked emitted radiation and the seed, confirms longitudinal coherence. Building on our scientific achievements, we anticipate a navigable pathway to extreme-ultraviolet wavelengths, paving the way towards smaller-scale free-electron lasers, unique tools for a multitude of applications in industry, laboratories and universities.

Heisenberg-Langevin approach to driven superradiance

Somech O., Shimshi Y. & Shahmoon E. (2023) Physical Review A.

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

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

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

Non-Hermitian optical design by coordinate transformations and mapping

Kresic I., Makris K. G., Brandstötter A., Leonhardt U. & Rotter S. (2023) International Conference on Metamaterials, Photonic Crystals and Plasmonics.

Coordinate transformations have been a powerful tool for design of metamaterial optical structures during the last 15 years [1]. In this talk I will discuss our recent research about theoretical methodologies for creating non-Hermitian transparent materials [2], invisibility cloaks [3], and light confinement [4], by coordinate transformations and mapping of electromagnetic field solutions.

The surface chemistry of ionic liquid-treated CsPbBr3 quantum dots

Crans K. D., Bain M., Bradforth S. E., Oron D., Kazes M. & Brutchey R. L. (2023) Journal of Chemical Physics.

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

Quantum light microscopy

Bowen W. P., Chrzanowski H. M., Oron D., Ramelow S., Tabakaev D., Terrasson A. & Thew R. (2023) Contemporary Physics.

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

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

Ohtsuki Y., Mikami S., Ajiki T. & Tannor D. J. (2023) Journal of the Chinese Chemical Society (Taipei).

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

Benchmarking the optimization optical machines with the planted solutions

Stroev N., Berloff N. G. & Davidson N. (2023) arXiv.org.

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

Disequilibrating azobenzenes by visible-light sensitization under confinement

Gemen J., Church J. R., Ruoko T. P., Durandin N., Białek M. J., Weißenfels M., Feller M., Kazes M., Odaybat M., Borin V. A., Kalepu R., Diskin-Posner Y., Oron D., Fuchter M. J., Priimagi A., Schapiro I. & Klajn R. (2023) Science (New York, N.Y.).

Photoisomerization of azobenzenes from their stable E isomer to the metastable Z state is the basis of numerous applications of these molecules. However, this reaction typically requires ultraviolet light, which limits applicability. In this study, we introduce disequilibration by sensitization under confinement (DESC), a supramolecular approach to induce the E-to-Z isomerization by using light of a desired color, including red. DESC relies on a combination of a macrocyclic host and a photosensitizer, which act together to selectively bind and sensitize E-azobenzenes for isomerization. The Z isomer lacks strong affinity for and is expelled from the host, which can then convert additional E-azobenzenes to the Z state. In this way, the host-photosensitizer complex converts photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed through direct photoexcitation.

Entropy Accumulation under Post-Quantum Cryptographic Assumptions

Merkulov I. & Arnon-Friedman R. (2023) arxiv.org.

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

Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules

Frenkel N., Scharf E., Lubin G., Levi A., Panfil Y. E., Ossia Y., Planelles J., Climente J. I., Banin U. & Oron D. (2023) ACS Nano.

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

Quantum Simulations of Interacting Systems with Broken Time-Reversal Symmetry

Shapira Y., Manovitz T., Akerman N., Stern A. & Ozeri R. (2023) Physical Review X.

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

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 APbI3 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 \u201cfluorescence recovery after photobleaching\u201d (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 APbI3 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-CsPbI3 and α-FAPbI3 than for MAPbI3. Furthermore, γ-CsPbI3 exhibits an intricate interplay between photoinduced darkening and brightening. We suggest possible explanations for the observed differences in SH behavior. This studys 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.

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 diamonds 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 1H spins of an organic sample on the diamond surface and measure 1H 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.

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.

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

Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2023) Physical Review A.

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

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

Hörner H., Rachbauer L. M., Rotter S. & Leonhardt U. (2023) Physical Review B.

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

A look under the tunnelling barrier via attosecond-gated interferometry

Kneller O., Azoury D., Federman Y., Krueger M., Uzan A. J., Orenstein G., Bruner B. D., Smirnova O., Patchkovskii S., Ivanov M. & Dudovich N. (2022) Nature Photonics.

Interferometry has been at the heart of wave optics since its early stages, resolving the coherence of the light field and enabling the complete reconstruction of the optical information it encodes. Transferring this concept to the attosecond time domain shed new light on fundamental ultrafast electron phenomena. Here we introduce attosecond-gated interferometry and probe one of the most fundamental quantum mechanical phenomena, field-induced tunnelling. Our experiment probes the evolution of an electronic wavefunction under the tunnelling barrier and records the phase acquired by an electron as it propagates in a classically forbidden region. We identify the quantum nature of the electronic wavepacket and capture its evolution within the optical cycle. Attosecond-gated interferometry has the potential to reveal the underlying quantum dynamics of strong-field-driven atomic, molecular and solid-state systems.

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

Misra A., Opatrny T. & Kurizki G. (2022) Physical Review. E.

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

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

Raanan D., Song M. S., Tisdale W. A. & Oron D. (2022) Applied Physics Letters.

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

Optimal Selective Orientation of Chiral Molecules Using Femtosecond Laser Pulses

Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) ArXiv.org..

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

Optimal Selective Orientation of Chiral Molecules Using Femtosecond Laser Pulses

Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) ArXiv.org..

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

Optimal Selective Orientation of Chiral Molecules Using Femtosecond Laser Pulses

Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) ArXiv.org..

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

Phase locking of lasers with Gaussian coupling

Reddy A. N. K., Mahler S., Goldring A., Pal V., Friesem A. A. & Davidson N. (2022) Optics Express.

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

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 atomion 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.

Quantum logic detection of collisions between single atomion 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.

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.

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.

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.

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.

Observation of interband Berry phase in laser-driven crystals

Uzan-Narovlansky A. J., Faeyrman L., Shames S., Narovlansky V., Xaio J., Arusi-Parpar T., Kneller O., Bruner B. D., Smirnova O., Silva R. E., Yan B., Jiménez-Galán Á., Ivanov M. & Dudovich N. (2022) .

We introduce and demonstrate a conceptually new manifestation of the Berry phase in light-driven crystals. We then experimentally demonstrate 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 high-order harmonics.

Impulsive SRS microscopy

Oron D., Raanan D. & Soffer Y. (2022) .

Impulsive spectroscopy provides a time-domain perspective of the active Raman modes of the specimen. As such, it serves as a complementary tool for the more common narrowband stimulated Raman techniques. In this chapter, we introduce the reader to the time-domain picture of vibrational excitation and detection, and discuss the advantages and disadvantages as compared to the narrowband variant of Raman scattering. We then proceed with mentioning recent advances in the experimental apparatus, aiming both at increasing the SNR and at increasing the delay scanning rate which constitutes a critical element in such time-domain techniques. We end up discussing preresonant impulsive Raman microspectroscopy and 2D impulsive Raman spectroscopy.

Photon Correlations in Spectroscopy and Microscopy

Lubin G., Oron D., Rossman U., Tenne R. & Yallapragada V. J. (2022) ACS Photonics.

Measurements of photon temporal correlations have been the mainstay of experiments in quantum optics. Over the past several decades, advancements in detector technologies have supported further extending photon correlation techniques to give rise to novel spectroscopy and imaging methods. This Perspective reviews the evolution of these techniques from temporal autocorrelations through multidimensional photon correlations to photon correlation imaging. State-of-the-art single-photon detector technologies are discussed, highlighting the main challenges and the unique current perspective of photon correlations to usher in a new generation of spectroscopy and imaging modalities.

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

Chan M. L., Aqua Z., Tiranov A., Dayan B., Lodahl P. & Sørensen A. S. (2022) Physical review. A.

We propose a deterministic yet fully passive scheme to transfer the quantum state from a frequency-encoded photon to the spin of a quantum dot mediated by a nanophotonic waveguide. We assess the quality of the state transfer by studying the effects of all relevant experimental imperfections on the state-transfer fidelity. We show that a transfer fidelity exceeding 95% is achievable for experimentally realistic parameters. Our work sets the stage for deterministic solid-state quantum networks tailored to frequency-encoded photonic qubits.

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

Mahler S., Tradonsky C., Pal V., Friesem A. A. & Davidson N. (2022) .

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

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.

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.

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.

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 lightmatter interactions have revolutionized our ability to probe and manipulate quantum systems at sub-femtosecond timescales1, opening routes to the all-optical control of electronic currents in solids at petahertz rates27. 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 lightmatter interaction induces notable modifications to the electronic and optical properties810, 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 fields 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 lightmatter interactions in strongly driven crystals and the sub-cycle modifications in their effective band structure.

Quantum suppression of cold reactions far from the quantum regime

Katz O., Pinkas M., Akerman N. & Ozeri R. (2022) arxiv.org.

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

Quantum suppression of cold reactions far from the quantum regime

Katz O., Pinkas M., Akerman N. & Ozeri R. (2022) arxiv.org.

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

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

Virzì S., Avella A., Piacentini F., Gramegna M., Opatrný T., Kofman A. G., Kurizki G., Gherardini S., Caruso F., Degiovanni I. P. & Genovese M. (2022) Physical review letters.

We experimentally demonstrate, for the first time, noise diagnostics by repeated quantum measurements, establishing the ability of a single photon subjected to random polarization noise to diagnose non-Markovian temporal correlations of such a noise process. Both the noise spectrum and temporal correlations are diagnosed by probing the photon with frequent (partially) selective polarization measurements. We show that noise with positive temporal correlations corresponds to our single photon undergoing a dynamical regime enabled by the quantum Zeno effect (QZE), whereas noise characterized by negative (anti) correlations corresponds to regimes associated with the anti-Zeno effect (AZE). This is the first step toward a novel noise spectroscopy based on QZE and AZE in single-photon state probing able to extract information on the noise while protecting the probe state, a conceptual paradigm shift with respect to traditional interferometric measurements.

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

Suzuki V. Y., Amorin L. H. C., Fabris G. S. L., Dey S., Sambrano J. R., Cohen H., Oron D. & La Porta F. A. (2022) Catalysts.

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

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

Chriki R., Mahler S., Tradonsky C., Friesem A. A. & Davidson N. (2022) Physical Review A.

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

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

Chriki R., Mahler S., Tradonsky C., Friesem A. A. & Davidson N. (2022) Physical Review A.

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

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

Tutunnikov I., Steinitz U., Gershnabel E., Hartmann J. M., Milner A. A., Milner V. & Averbukh I. S. (2022) .

We present a theoretical-experimental study of polarization rotation of light traveling through a gas of fast-spinning molecules. The long-term behavior of the polarization angle can be used for probing relaxation dynamics in molecular gases.

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

Mor Markovsky O. E., Ohana T., Borne A., Diskin Posner Y., Asher M., Yaffe O., Shanzer A. & Dayan B. (2022) ACS Photonics.

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

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

Smartsev S., Tata S., Liberman A., Adelberg M., Mohanty A., Levine E., Seeman O., Wan Y., Kroupp E., Lahaye R., Thaury C. & Malka V. (2022) Journal of optics (2010).

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

Transforming Space with Non-Hermitian Dielectrics

Krešić I., Makris K. G., Leonhardt U. & Rotter S. (2022) Physical review letters.

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

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

Levy D., Andriyash I. A., Haessler S., Kaur J., Ouillé M., Flacco A., Kroupp E., Malka V. & Lopez-Martens R. (2022) Physical Review Accelerators and Beams.

Proton beams with up to 100 pC bunch charge, 0.48 MeV cutoff energy, and divergence as low as 3° were generated from solid targets at kHz repetition rate by a few-mJ femtosecond laser under controlled plasma conditions. The beam spatial profile was measured using a small aperture scanning time-of-flight detector. Detailed parametric studies were performed by varying the surface plasma scale length from 8 to 80 nm and the laser pulse duration from 4 fs to 1.5 ps. Numerical simulations are in good agreement with observations and, together with an in-depth theoretical analysis of the acceleration mechanism, indicate that high repetition rate femtosecond laser technology could be used to produce few-MeV proton beams for applications.

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

Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) arxiv.org.

Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond (fs) pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed fs probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

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

Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) arxiv.org.

Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond (fs) pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed fs probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

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

Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) arxiv.org.

Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond (fs) pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed fs probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

Self-Healing and Light-Soaking in MAPbI3: The Effect of H2O

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 \u201cself-healing.\u201d Here two-photon (2P) absorption is used to effect light-induced modifications within MAPbI3 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 MAPbI3. 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 \u201clight-soaking\u201d) 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 H2O, 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 H2O, 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.

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.

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.

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.

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.

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) 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.

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

Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) 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.

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

Xu L., Tutunnikov I., Prior Y. & Averbukh I. S. (2022) Journal of Chemical Physics.

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

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

Tenne R., Lubin G., Ulku A. C., Antolovic I. M., Burri S., Karg S., Yallapragada V. J., Bruschini C., Charbon E. & Oron D. (2022) .

Spectrometry of a quantum state of light is a fundamental challenge with practical implications. Here, we demonstrate how such a technique can super-resolve the exciton and biexciton energies in a single quantum dot at room temperature.

Femtosecond Rotational Dynamics of D2 Molecules in Superfluid Helium Nanodroplets

Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) Physical review letters.

Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed femtosecond probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

Femtosecond Rotational Dynamics of D2 Molecules in Superfluid Helium Nanodroplets

Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) Physical review letters.

Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed femtosecond probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

Femtosecond Rotational Dynamics of D2 Molecules in Superfluid Helium Nanodroplets

Qiang J., Zhou L., Lu P., Lin K., Ma Y., Pan S., Lu C., Jiang W., Sun F., Zhang W., Li H., Gong X., Averbukh I. S., Prior Y., Schouder C. A., Stapelfeldt H., Cherepanov I. N., Lemeshko M., Jäger W. & Wu J. (2022) Physical review letters.

Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed femtosecond probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.

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

Nasi H., Chiara di Gregorio M., Wen Q., Shimon L. J. W., Kaplan-Ashiri I., Bendikov T., Leitus G., Kazes M., Oron D., Lahav M. & van der Boom M. E. (2022) Angewandte Chemie (International ed.).

We show that metal-organic frameworks, based on tetrahedral pyridyl ligands, can be used as a morphological and structural template to form a series of isostructural crystals having different metal ions and properties. An iterative crystal-to-crystal conversion has been demonstrated by consecutive cation exchanges. The primary manganese-based crystals are characterized by an uncommon space group ( P622 ). The packing includes chiral channels that can mediate the cation exchange, as indicated by energy-dispersive X-ray spectroscopy on microtome-sectioned crystals. The observed cation exchange is in excellent agreement with the Irving-Williams series (Mn < Fe < Co < Ni < Cu > Zn) associated with the relative stability of the resulting coordination nodes. Furthermore, we demonstrate how the metal cation controls the optical and magnetic properties. The crystals maintain their morphology, allowing a quantitative comparison of their properties at both the ensemble and single-crystal level.

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

Gemen J., Białek M. J., Kazes M., Shimon L. J. W., Feller M., Semenov S. N., Diskin-Posner Y., Oron D. & Klajn R. (2022) Chem.

Confinement within molecular cages can dramatically modify the physicochemical properties of the encapsulated guest molecules, but such host-guest complexes have mainly been studied in a static context. Combining confinement effects with fast guest exchange kinetics could pave the way toward stimuli-responsive supramolecular systemsand ultimately materialswhose desired properties could be tailored \u201con demand\u201d 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.

Casimir Cosmology

Leonhardt U. (2022) .

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 Einsteins 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 fleld 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 \u201cThe State of the Quantum Vacuum: Casimir Physics in the 2020s\u201d edited by K. A. Milton. It may also be interesting for other physicists and engineers who wish to have a concise introduction to cosmology.

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 shells1. This isolation, however, impedes the ability to manipulate and control them by optical means or by coupling to other spin gases24. 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 information5,6.

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 88Sr+ 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.

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 88Sr+ 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 lasermatter 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 lightand new approaches to light-based computation.

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 lightand 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.

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.

Observation of Mechanical Faraday Effect in Gaseous Media

Milner A. A., Steinitz U., Averbukh I. S. & Milner V. (2021) Physical Review Letters.

We report the experimental observation of the rotation of the linear polarization of light propagating in a gas of fast-spinning molecules (molecular superrotors). In the observed effect, related to Fermi's prediction of "polarization drag"by a rotating medium, the vector of linear polarization tilts in the direction of molecular rotation. We use an optical centrifuge to bring the molecules in a gas sample to ultrafast unidirectional rotation and measure the polarization drag angles of the order of 10-4 rad (with an experimental uncertainty about 10-6 rad) over the propagation distance of the order of 1 mm in a number of gases under ambient conditions. We demonstrate an all-optical control of the drag magnitude and direction and investigate the robustness of the mechanical Faraday effect with respect to molecular collisions.

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.

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.

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 0.11 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.

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.

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: 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 todays 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 acidbase 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 effecta 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.

Erratum: High-resolution digital spatial control of a highly multimode laser(Optica (2021) 8 (880-884) DOI: 10.1364/OPTICA.423140)

Tradonsky C., Mahler S., Cai G., Pal V., Chriki R., Friesem A. A. & Davidson N. (2021) Optica.

In Ref. [1], typographical errors were found in the labels of Figs. 5(b)5(d) where the propagation distances z were wrong. The correct propagation distances can be found in the figure caption and in the correct version of the figure provided here.

Erratum: High-resolution digital spatial control of a highly multimode laser(Optica (2021) 8 (880-884) DOI: 10.1364/OPTICA.423140)

Tradonsky C., Mahler S., Cai G., Pal V., Chriki R., Friesem A. A. & Davidson N. (2021) Optica.

In Ref. [1], typographical errors were found in the labels of Figs. 5(b)5(d) where the propagation distances z were wrong. The correct propagation distances can be found in the figure caption and in the correct version of the figure provided here.

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.

Exact Mapping Between a Laser Network and the Classical XY Hamiltonian

Gershenzon I., Arwas G., Gadasi S., Tradonsky C., Friesem A., Raz O. & Davidson N. (2021) Optics InfoBase Conference Papers.

We demonstrate experimentally and validate theoretically an exact mapping between coupled-lasers networks and classical spin Hamiltonians by adjusting the loss rate of the individual lasers.

Exact Mapping Between a Laser Network and the Classical XY Hamiltonian

Gershenzon I., Arwas G., Gadasi S., Tradonsky C., Friesem A., Raz O. & Davidson N. (2021) Optics InfoBase Conference Papers.

We demonstrate experimentally and validate theoretically an exact mapping between coupled-lasers networks and classical spin Hamiltonians by adjusting the loss rate of the individual lasers.

Bright multiplexed source of indistinguishable single photons with tunable GHz-bandwidth at room temperature

Davidson O., Finkelstein R., Poem E. & Firstenberg O. (2021) New Journal of Physics.

Narrowband single photons that couple well to atomic ensembles could prove essential for future quantum networks, but the efficient generation of such photons remains an outstanding challenge. We realize a spatially-multiplexed heralded source of single photons that are inherently compatible with the commonly employed D2 line of rubidium. Our source is based on four-wave mixing in hot rubidium vapor, requiring no laser cooling or optical cavities, and generates single photons with high rate and low noise. We use Hong-Ou-Mandel interference to verify the indistinguishability of the photons generated in two different (multiplexed) channels. We further demonstrate a five-fold tunability of the photons' temporal width. The experimental results are well reproduced by a theoretical model.

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 materials18. 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 spinlattice relaxation times T1 of 1317 μs with estimated spin coherence times T2 of less than 1 μs. Our results provide further insight into the structure, composition and dynamics of single optically active spin defects in hexagonal boron nitride.

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

Tannor D. J. (2021) arxiv.org.

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

Fair Sampling with a Highly Parallel Laser Simulator

Pal V., Mahler S., Friesem A. A. & Davidson N. (2021) .

We present efficient fair sampling of ground-state manifold of XY spin Hamiltonian based on dissipatively coupled lasers that includes a massive parallelism. Our simulator could potentially be exploited to address various combinatorial optimization problems.

Fair Sampling with a Highly Parallel Laser Simulator

Pal V., Mahler S., Friesem A. A. & Davidson N. (2021) .

We present efficient fair sampling of ground-state manifold of XY spin Hamiltonian based on dissipatively coupled lasers that includes a massive parallelism. Our simulator could potentially be exploited to address various combinatorial optimization problems.

Simultaneous measurements of high-order harmonics, accelerated electrons and protons emitted from relativistic plasma mirrors

Kaur J., Levy D., Ouille M., Andriyash I., Kroupp E., Malka V., Faure J., Haessler S. & Lopez-Martens R. (2021) .

We report the first simultaneous measurements of high-harmonic generation, accelerated electron and proton beams generated on relativistic plasma mirrors with controlled scale length using laser pulses with duration tunable from 27 fs to sub-4 fs.

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.

SPAD array technology enables fluctuation-contrast super-resolution in a confocal microscope

Tenne R., Makowski A., Lubin G., Antolovic M., Rossman U., Sroda A., Charbon E., Bruschini C., Lapkiewicz R. & Oron D. (2021) .

A fluorescence correlation contrast is as traightforward a pproach to super-resolution imaging. Combining a SPAD array with a novel detection scheme (ISM), we obtain images with up to x4 times resolution enhancement.

Echoes in a single quantum Kerr-nonlinear oscillator

Tutunnikov I., Rajitha K. V. & Averbukh I. S. (2021) Optics InfoBase Conference Papers.

We theoretically study the echo phenomenon in a single impulsively excited (\u201ckicked\u201d) Kerr-nonlinear oscillator. These echoes may be useful for studying decoherence processes in a number of systems related to quantum information processing.

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.

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.

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.

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.

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 have been and still are important elusive tasks in molecular physics and chemistry, and a variety of methods have been introduced over the years to achieve these goals. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces in these molecules an enantioselective orientation. 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. This persistent orientation may enhance the deflection of the molecules in inhomogeneous electromagnetic fields, potentially leading to viable separation techniques.

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 have been and still are important elusive tasks in molecular physics and chemistry, and a variety of methods have been introduced over the years to achieve these goals. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces in these molecules an enantioselective orientation. 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. This persistent orientation may enhance the deflection of the molecules in inhomogeneous electromagnetic fields, potentially leading to viable separation techniques.

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 have been and still are important elusive tasks in molecular physics and chemistry, and a variety of methods have been introduced over the years to achieve these goals. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces in these molecules an enantioselective orientation. 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. This 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.

SPAD array technology enables fluctuation-contrast super-resolution in a confocal microscope

Tenne R., Makowski A., Lubin G., Antolovic M., Rossman U., Sroda A., Charbon E., Bruschini C., Lapkiewicz R. & Oron D. (2021) Optics InfoBase Conference Papers.

A fluorescence c orrelation c ontrast i s a s traightforward a pproach t o super-resolution imaging.

Remanent Polarization and Strong Photoluminescence Modulation by an External Electric Field in Epitaxial CsPbBr3Nanowires

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 CsPbBr3 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.

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 MetalOrganic 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.

Metalorganic 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 no-communication 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 executionthe 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.

Conceptual design report for the LUXE experiment

Abramowicz H., Acosta U., Altarelli M., Aßmann R., Bai Z., Behnke T., Benhammou Y., Blackburn T., Boogert S., Borysov O., Borysova M., Brinkmann R., Bruschi M., Burkart F., Büßer K., Cavanagh N., Davidi O., Decking W., Dosselli U., Elkina N., Fedotov A., Firlej M., Fiutowski T., Fleck K., Gostkin M., Grojean C., Hallford J., Harsh H., Hartin A., Heinemann B., Heinzl T., Helary L., Hoffmann M., Huang S., Huang X., Idzik M., Ilderton A., Jacobs R., Kämpfer B., King B., Lahno H., Levanon A., Levy A., Levy I., List J., Lohmann W., Ma T., Macleod A. J., Malka V., Meloni F., Mironov A., Morandin M., Moron J., Negodin E., Perez G., Pomerantz I., Pöschl R., Prasad R., Quéré F., Ringwald A., Rödel C., Rykovanov S., Salgado F., Santra A., Sarri G., Sävert A., Sbrizzi A., Schmitt S., Schramm U., Schuwalow S., Seipt D., Shaimerdenova L., Shchedrolosiev M., Skakunov M., Soreq Y., Streeter M., Swientek K., Hod N. T., Tang S., Teter T., Thoden D., Titov A. I., Tolbanov O., Torgrimsson G., Tyazhev A., Wing M., Zanetti M., Zarubin A., Zeil K., Zepf M. & Zhemchukov A. (2021) European Physical Journal: Special Topics.

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) field strengths to be probed where the coupling to charges becomes non-perturbative 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 350 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.

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.

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 a 22 + a 11-2a 12. 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.

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 a 22 + a 11-2a 12. 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.

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 a 22 + a 11-2a 12. 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 preparationboth 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.

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 preparationboth 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 measurements of an 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 process to occur. In the quantum regime of low energies, the cross section can greatly vary 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 0.2-12mK×kB, by shuttling ultracold atoms trapped in an optical-lattice across a radio-frequency trapped ion. Using 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 200μK×kB, limited by drifts in the ion's excess micromotion compensation and can be reduced to the tens of μK×kB 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 nonadiabatic 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 the possibility to search for atom-ion quantum signatures such as shape resonances.

High-energy-resolution measurements of an 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 process to occur. In the quantum regime of low energies, the cross section can greatly vary 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 0.2-12mK×kB, by shuttling ultracold atoms trapped in an optical-lattice across a radio-frequency trapped ion. Using 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 200μK×kB, limited by drifts in the ion's excess micromotion compensation and can be reduced to the tens of μK×kB 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 nonadiabatic 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 the possibility to search for atom-ion quantum signatures such as shape resonances.

High-energy-resolution measurements of an 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 process to occur. In the quantum regime of low energies, the cross section can greatly vary 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 0.2-12mK×kB, by shuttling ultracold atoms trapped in an optical-lattice across a radio-frequency trapped ion. Using 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 200μK×kB, limited by drifts in the ion's excess micromotion compensation and can be reduced to the tens of μK×kB 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 nonadiabatic 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 the possibility 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 (1977) 2738) 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.

Nonlinear interferometry enables coherent heat machine operation

Opatrný T., Bräuer Š., Kofman A. G., Misra A., Meher N., Firstenberg O., Poem E. & Kurizki G. (2021) arXiv.org.

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

Nonlinear interferometry enables coherent heat machine operation

Opatrný T., Bräuer Š., Kofman A. G., Misra A., Meher N., Firstenberg O., Poem E. & Kurizki G. (2021) arXiv.org.

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

Continuous Protection of a Collective State from Inhomogeneous Dephasing

Finkelstein R., Lahad O., Cohen I., Davidson O., Kiriati S., Poem E. & Firstenberg O. (2021) Physical Review X.

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

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

Dong H., Ghosh A., Kim M. B., Li S., Svidzinsky A. A., Zhang Z., Kurizki G. & Scully M. O. (2021) European Physical Journal: 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 \u201csink\u201d.

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 12 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.

Boosting photonic quantum computation with moderate nonlinearity

Pick A., Matekole E. S., Aqua Z., Guendelman G., Firstenberg O., Dowling J. P. & Dayan B. (2021) .

We present a new pathway towards fault-tolerant photonic quantum computing by using moderate nonlinearity to improve elementary computation operations. This improvement can lead to a three orders-of-magnitude reduction of the resource overhead in large-scale computations.

Boosting photonic quantum computation with moderate nonlinearity

Pick A., Matekole E. S., Aqua Z., Guendelman G., Firstenberg O., Dowling J. P. & Dayan B. (2021) .

We present a new pathway towards fault-tolerant photonic quantum computing by using moderate nonlinearity to improve elementary computation operations. This improvement can lead to a three orders-of-magnitude reduction of the resource overhead in large-scale computations.

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.

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) European Physical Journal: 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 ShockleyQueisser 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., DArcy 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 810 years.

Long-Lived Entanglement Generation of Nuclear Spins Using Coherent Light

Katz O., Shaham R., Polzik E. S. & Firstenberg O. (2020) Physical Review Letters.

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

Echoes in unidirectionally rotating molecules

Xu L., Tutunnikov I., Zhou L., Lin K., Qiang J., Lu P., Prior Y., Averbukh I. S. & Wu J. (2020) Physical Review A.

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

Echoes in unidirectionally rotating molecules

Xu L., Tutunnikov I., Zhou L., Lin K., Qiang J., Lu P., Prior Y., Averbukh I. S. & Wu J. (2020) Physical Review A.

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

Echoes in unidirectionally rotating molecules

Xu L., Tutunnikov I., Zhou L., Lin K., Qiang J., Lu P., Prior Y., Averbukh I. S. & Wu J. (2020) Physical Review A.

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

Error-corrected gates on an encoded qubit

Reinhold P., Rosenblum S., Ma W., Frunzio L., Jiang L. & Schoelkopf R. J. (2020) Nature Physics.

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

Identification of molecular quantum states using phase-sensitive forces

Najafian K., Meir Z., Sinhal M. & Willitsch S. (2020) Nature Communications.

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

Giant polarization drag in a gas of molecular super-rotors

Steinitz U. & Averbukh I. S. (2020) Physical Review A.

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

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

Nevo I., Jahn S., Kretzschmar N., Levantino M., Feldman Y., Naftali N., Wulff M., Oron D. & Leiserowitz L. (2020) Journal of Chemical Physics.

The induction of homogeneous and oriented ice nucleation has to date not been achieved. Here, we report induced nucleation of ice from millimeter sized supercooled water drops illuminated by ns-optical laser pulses well below the ionization threshold making use of particular laser beam configurations and polarizations. Employing a 100 ps synchrotron x-ray pulse 100 ns after each laser pulse, an unambiguous correlation was observed between the directions and the symmetry of the laser fields and that of the H-bonding arrays of the induced ice crystals. Moreover, an analysis of the x-ray diffraction data indicates that, in the main, the induced nucleation of ice is homogeneous at temperatures well above the observed and predicted values for supercooled water.

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

Ludwig A., Serna P. A., Morgenstein L., Yang G., Bar-Elli O., Ortiz G., Miller E., Oron D., Grupi A., Weiss S. & Antoine T. (2020) ACS Photonics.

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

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

Rosenberg Y., Drori J., Bermudez D. & Leonhardt U. (2020) Optics Express.

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

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

Pan Y., Zhang J., Cohen E., Wu C. w., Chen P. X. & Davidson N. (2020) Nature Physics.

Quantum measurement remains a puzzle through its stormy history from the birth of quantum mechanics to state-of-the-art quantum technologies. Two complementary measurement schemes have been widely investigated in a variety of quantum systems: von Neumanns projective strong measurement and Aharonovs weak measurement. Here, we report the observation of a weak-to-strong measurement transition in a single trapped 40Ca+ ion system. The transition is realized by tuning the interaction strength between the ions 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 ions 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 systemapparatus 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.

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.

Progress towards laser plasma based free electron laser on COXINEL

Couprie M. E., André T., Blache F., Bouvet F. o., Dietrich Y., Duval J. P., El-Ajjouri M., Ghaith A., Herbeaux C., Hubert N., Kitégi C., Khojoyan M., Labat M., Leclercq N., Lestrade A., Loulergue A., Marcouillé O., Marteau F., Oumbarek-Espinos D., Rommeluére P., Sebdaoui M., Tavakoli K., Valleáu M., Corde S., Gautier J., Goddet J. P., Kononenko O., Lambert G., Tafzi A., Phuoc K. T., Thaury C., Bielawski S., Roussel E., Szwaj C., Andriyash I., Malka V. & Smartsev S. (2020) Journal of Physics: Conference Series.

The Free Electron Laser (FEL) application of Laser Plasma Acceleration (LPA) requires the handling of the energy spread and divergence. The COXINEL manipulation line, designed and built at SOLEIL for this purpose, consists of high gradient quadrupoles for divergence handling and a decompression chicane for energy sorting, enabling FEL amplification with baseline parameters. Installed at Laboratoire d'Optique Appliquee (LOA), it uses robust electrons generated and accelerated by ionization injection using a 30 TW laser. We report here on the work progress towards a FEL demonstration. The LPA measured electron beam characteristics deviates from the baseline reference case. After the installation of the equipment, the electron beam transport has first been optimized. The electron position and dispersion are independently adjusted. Then, undulator radiation has been measured. The spectral purity is controlled via the energy spread adjusted in the slit located in the chicane. FEL effect demonstration is within reach, with currently achieved performance on different LPA experiments.

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

Pal V., Mahler S., Tradonsky C., Friesem A. A. & Davidson N. (2020) 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.

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

Pal V., Mahler S., Tradonsky C., Friesem A. A. & Davidson N. (2020) 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.

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.

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.

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.

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.

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.

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 171Yb + 40Ca + and 138Ba + 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 \u201cdevice-independent quantum cryptography\u201d. 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 \u201cprivatization\u201d 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.

Electrostatic shock acceleration of ions in near-critical-density plasma driven by a femtosecond petawatt laser

Singh P. K., Pathak V. B., Shin J. H., Choi I. W., Nakajima K., Lee S. K., Sung J. H., Lee H. W., Rhee Y. J., Aniculaesei C., Kim C. M., Pae K. H., Cho M. H., Hojbota C., Lee S. G., Mollica F., Malka V., Ryu C., Kim H. T. & Nam C. H. (2020) Scientific Reports.

With the recent advances in ultrahigh intensity lasers, exotic astrophysical phenomena can be investigated in laboratory environments. Collisionless shock in a plasma, prevalent in astrophysical events, is produced when a strong electric or electromagnetic force induces a shock structure in a time scale shorter than the collision time of charged particles. A near-critical-density (NCD) plasma, generated with an intense femtosecond laser, can be utilized to excite a collisionless shock due to its efficient and rapid energy absorption. We present electrostatic shock acceleration (ESA) in experiments performed with a high-density helium gas jet, containing a small fraction of hydrogen, irradiated with a 30 fs, petawatt laser. The onset of ESA exhibited a strong dependence on plasma density, consistent with the result of particle-in-cell simulations on relativistic plasma dynamics. The mass-dependent ESA in the NCD plasma, confirmed by the preferential reflection of only protons with two times the shock velocity, opens a new possibility of selective acceleration of ions by electrostatic shock.

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

Wan Y., Andriyash I. A., Lu W., Mori W. B. & Malka V. A. (2020) Physical Review Letters.

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

Echo in a single vibrationally excited molecule

Qiang J., Tutunnikov I., Lu P., Lin K., Zhang W., Sun F., Silberberg Y., Prior Y., Averbukh I. S. & Wu J. (2020) Nature Physics.

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

Echo in a single vibrationally excited molecule

Qiang J., Tutunnikov I., Lu P., Lin K., Zhang W., Sun F., Silberberg Y., Prior Y., Averbukh I. S. & Wu J. (2020) Nature Physics.

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

Echo in a single vibrationally excited molecule

Qiang J., Tutunnikov I., Lu P., Lin K., Zhang W., Sun F., Silberberg Y., Prior Y., Averbukh I. S. & Wu J. (2020) Nature Physics.

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

Attosecond spectral singularities in solid-state high-harmonic generation

Uzan A. J., Orenstein G., Bruner B. D., Jimenez-Galan Á., McDonald C., Silva R. E., Klimkin N. D., Blanchet V., Arusi-Parpar T., Krüger M., Rubtsov A. N., Smirnova O., Ivanov M., Yan B., Brabec T. & Dudovich N. (2020) .

Using high-harmonic generation spectroscopy, we reveal the underlying attosecond dynamics in multi-band solid-state systems. We identify the mapping of spectral caustics into the high-harmonic spectrum, and probe the structure of multiple unpopulated high conduction bands.

Spatiotemporal rotational dynamics of laser-driven molecules

Lin K., Tutunnikov I., Ma J., Qiang J., Zhou L., Faucher O., Prior Y., Averbukh I. S. & Wu J. (2020) Advanced Photonics.

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

Spatiotemporal rotational dynamics of laser-driven molecules

Lin K., Tutunnikov I., Ma J., Qiang J., Zhou L., Faucher O., Prior Y., Averbukh I. S. & Wu J. (2020) Advanced Photonics.

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

Spatiotemporal rotational dynamics of laser-driven molecules

Lin K., Tutunnikov I., Ma J., Qiang J., Zhou L., Faucher O., Prior Y., Averbukh I. S. & Wu J. (2020) Advanced Photonics.

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

Enhanced laser-driven proton acceleration with gas-foil targets

Levy D., Davoine X., Debayle A., Gremillet L. & Malka V. (2020) Journal of Plasma Physics.

We study numerically the mechanisms of proton acceleration in gas-foil targets driven by an ultraintense femtosecond laser pulse. The target consists of a near-critical-density hydrogen gas layer of a few tens of microns attached to a 2 μm-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: alignmentantialignment 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. C60 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 (14N@C60) within a C60 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.

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.

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.