Seminars

Neutral atom quantum computers: current status and next challenges

Neutral atom quantum processors combine scalability, high fidelities, and parallel, efficient control, making them a highly promising platform for large-scale universal quantum computing. In this talk, I will introduce the fundamentals of neutral atom quantum computing and highlight recent advances in the field, focusing on experimental achievements from the Harvard and Quera teams. These include the demonstration of a logical qubit quantum processor and a digital simulation of the Kitaev model at Harvard, as well as the realization of magic state distillation at Quera. I will also briefly touch on key theoretical developments in quantum error correction. To conclude, I will discuss technological challenges in building a universal fault-tolerant quantum computer and outline potential strategies to overcome them.

Shaping Optical Forces: From Laser-Driven Lightsails to Optomechanical Nonlinear Dynamics

Optical forces have driven transformative breakthroughs in science, including optical tweezers, atom cooling, and Bose-Einstein condensation, each recognized with a Nobel Prize in Physics. Recent years have seen great progress in nanophotonics, allowing us to manipulate light at the nanoscale by designing materials with complex geometries of sub-wavelength structures. The merging of optical forces and nanophotonics has led to the emerging field of optomechanical control of nanostructured objects. This new paradigm enables great flexibility in designing optical forces, allowing to manipulate large objects over long distances and thus unlocking exciting opportunities in both fundamental science and technological innovation.
In this talk, I will present my research in this area, introducing novel methods for shaping and characterizing optical forces, and studying the resulting optomechanical nonlinear dynamics. I will first introduce our platform for simultaneously measuring optical forces and powers, utilizing the coupled thermal, mechanical, and optical dynamics induced by the driving laser beam. Using this platform, we characterized the forces acting on a thin membrane, which is relevant to applications such as laser-driven lightsails for space exploration. Next, I will demonstrate how nanopatterning can be used to design systems capable of pulling objects over large distances using optical forces. Finally, I will discuss the intriguing nonlinear dynamics observed in our membranes. Within the bistable regime induced by Duffing nonlinearity, stochastic thermal fluctuations allow us to control the intermodal energy exchange rate, leading to significant optomechanical nonlinearities.
 

New Avenues for Quantum Information Processing with Light-Matter Interactions

Light-matter interaction (LMI) underpins numerous quantum technologies, yet persistent challenges—such as decoherence, scalability, and speed—limit the advancement of quantum information processing (QIP) in this promising platform. These limitations motivate the search for alternative quantum hardware leveraging LMI to overcome these barriers and unveil new opportunities for QIP.
In this seminar, I will demonstrate how combining diverse concepts, components, and building blocks in quantum optics leads to such novel approaches for QIP. First, I will introduce free electrons as a new and promising resource in quantum optics, enabling ultrafast operation, strong coupling, and single-photon nonlinearities in cavity quantum electrodynamics (QED). Next, I will show how the integration of concepts from nonlinear optics into waveguide QED unlocks novel schemes for many-body entanglement generation and enables access to exotic physics in atomic arrays. Finally, I will present a scalable architecture for processing high-dimensional photonic entanglement, inspired by the variational principle in physics and realized through self-configuring photonic networks.

[1] Karnieli*, Tsesses*, et al PRX Quantum 5, 010339 (2024)
[2] Karnieli and Fan, Science Advances 9, eadh2425 (2023)
[3] Karnieli*, Roques-Carmes*, et al, ACS Photonics 11, 3401 (2024)
[4] Karnieli et al, accepted to Physical Review Research (2024)
[5] Roques-Carmes*, Karnieli* et al, arXiv:2407.16849 (2024)
[6] Karnieli*, Roques-Carmes*, et al (submitted to CLE0 2025)

PhD defense: Collective quantum light-matter interfaces with atomic arrays

Quantum optical platforms, based on the manipulation of atoms and photons, play an essential role in the exploration of quantum science and technology. Of crucial importance is the ability to establish an interface between photons and atoms. Such an interface allows to benefit from the low-loss propagation of photons combined with the quantum coherence or nonlinearity of atoms, with applications ranging from quantum memories and information to many-body physics. In this talk I will present our theoretical work on collective light-matter interfaces where many atoms interact collectively with photons. Our approach is based on the mapping of many-body atom-photon problems to a generic 1D model of light interacting with a collective dipole. This provides a unified framework for the analysis of collective light-matter coupling in various relevant platforms such as optical lattices and tweezer arrays. In addition, it will be shown how these collective systems support efficient entanglement generation for quantum networks, metrology, and scalable quantum information processing.

Fermions in an Optical Box

For the past two decades harmonically trapped ultracold atomic gases have been used with great success to study fundamental many-body physics in flexible experimental settings. However, the resulting gas density inhomogeneity in those traps has made it challenging to study paradigmatic uniform-system physics (such as critical behavior near phase transitions) or complex quantum dynamics. The realization of homogeneous quantum gases trapped in optical boxes has been a milestone in quantum simulation [1]. These textbook systems have proved to be a powerful playground by simplifying the interpretation of experimental measurements, by making more direct connections to theories of the many-body problem that generally rely on the translational symmetry of the system, and by altogether enabling previously inaccessible experiments.  

I will give an overview of recent studies on the quantum many-body physics of fermions in a box of light. These studies span the few-body recombination physics of multi-component fermions [2,3], the observation of the fermionic quantum Joule-Thomson effect [4], the strong-drive spectroscopy of Fermi-polaron quasiparticles [5], and the observation of the Lindhard response [6].

These studies have led to some surprising results (including an open puzzle on three-component fermions [3]), highlighting how spatial homogeneity not only provide quantitative advantages, but can also unveil truly unexpected outcomes

References
[1] N. Navon, R.P. Smith, Z. Hadzibabic, Nature Phys. 17, 1334 (2021)
[2] Y. Ji et al., Phys. Lev. Lett 129, 203402 (2022)
[3] G.L. Schumacher et al., arXiv:2301.02237
[4] Y. Ji et al., Phys. Lev. Lett 132, 153402 (2024)
[5] F.J. Vivanco et al., arXiv:2308.05746, Nature Phys. in press (2025)
[6] S. Huang et al., arXiv:2407.13769

Quantum Magnetometry in Search of Dark Matter

Quantum Magnetometry in Search of Dark Matter

Dr. Itay Bloch

When bosonic Dark Matter (DM) has an ultra-light mass, it acts as a classical, coherent field. In many cases, and specifically for many models of axion-like-particles, this field has a magnetic-like effect on spins, and can therefore be measured by spin-based quantum magnetometers. In this seminar, I will explain the workings of quantum magnetometers, focusing on comagnetometers, which simultaneously utilize several species of atoms to achieve a variety of benefits. I will discuss my work on the self compensating comagnetometer, and spotlight my recent proposal for a new sensor called the RoW comag. I will also discuss my work as one of the founding members of the Noble and Alkali Spin Detectors for Ultralight Coherent darK matter (NASDUCK) collaboration, which was formed a few years ago to measure DM with magnetometers. I will also touch upon my current involvement in multiple other spin-based magnetometry experiments. I will finish with an ambitious magnetometry method I am working on, which uses what is normally seen as irreducible quantum noise, as a signal instead. This new metrological strategy may unlock new directions for spin-based searches, allowing sensitivity to highly motivated DM models.

Liquid light in synthetic lattices for frequency comb generation [Special seminar]

Liquid light in synthetic lattices for frequency comb generation

Alexander Dikopoltsev

Institute for quantum electronics , ETH Zurich, Zurich, Switzerland

The study of light dynamics in the frequency domain has been pivotal for applications in metrology and communications. One of the most impactful states is the optical frequency comb—a broadband light state where frequencies are equally spaced. To generate these combs, we rely on two key processes: nonlinear frequency proliferation and stabilization. When frequency proliferation occurs inside multimode lasers, the gain recovery time emerges as a critical factor for stabilization. Over 40 years ago, the stabilization process was described by slow and selective dissipation, like gain curvature in frequency or gain modulation in time [1]. However, recent advances in semiconductor-based frequency-comb sources have shown that when the gain recovery time becomes very short [2], the dynamics of light in the frequency domain becomes radically different [3-6].

In my talk, I will present the exploration of light dynamics in a discrete frequency space, when gain recovery times are fast [7,8]. I will show that light traveling through a medium with fast gain saturation transforms it into a type of liquid, which forces coherent dynamics despite destabilization processes, for example quenching or dephasing. This liquid state of light allows to explore fully the synthetic lattice in the frequency space, reaching its maximal limit given by the linear system. Such a platform not only advances our understanding of quench dynamics in non-equilibrium systems, but can also lead to innovative quantum inspired devices, like the recently discovered quantum walk comb source [7].

References

[1] H. Haus, “A theory of forced mode locking” IEEE J. Quantum Electron. 11, 323–330 (1975).

[2] U. Senica, A. Dikopoltsev, et al., “Frequency-Modulated Combs via Field-Enhancing Tapered Waveguides”, Laser Photonics Rev, 2300472 (2023).

[3] J. B. Khurgin, et al. "Coherent frequency combs produced by self frequency modulation in quantum cascade lasers." APL 104.8 (2014).

[4] N. Opačak, et al., “Theory of frequency-modulated combs in lasers with spatial hole burning, dispersion, and Kerr nonlinearity” Phys. Rev. Lett. 123, 243902 (2019).

[5] D. Burghoff, "Unravelling the origin of frequency modulated combs using active cavity mean-field theory." Optica 7.12 (2020): 1781-1787.

[6] M. Piccardo, et al. "Frequency combs induced by phase turbulence." Nature 582.7812 (2020): 360-364.

[7] I. Heckelmann*, M. Bertrand*, A. Dikopoltsev*, et al., “Quantum walk comb in a fast gain laser”, Science 382, 434-438 (2023).

[8] A. Dikopoltsev, et al. "Quench dynamics of Wannier-Stark states in an active synthetic photonic lattice." arXiv:2405.04774 (2024)

Journal club

Bose-Einstein condensation of photons in micro-cavities

Amit Pando

When bosons are at a sufficiently low temperature and high density, they undergo a phase transition to a Bose-Einstein condensate. Despite being the most common example of bosons, a thermal gas of photons does not undergo this phase transition regardless of temperature. In 2010, it was shown that dye-filled micro-cavities can induce condensation of photons, exhibiting many of the physical hallmarks of BECs. In the past 15 years, these systems have been explored further, and more recently, it was demonstrated that photon condensation can occur even in “typical” semiconductor microcavities and VCSELs. In this talk, I will give a brief overview of the physics of photonic BECs and present some of the recent results in the field.

[1] Klaers, Jan, et al. "Bose–Einstein condensation of photons in an optical microcavity." Nature 468.7323 (2010): 545-548.

[2] Schofield, Ross C., et al. "Bose–Einstein condensation of light in a semiconductor quantum well microcavity." Nature Photonics 18.10 (2024): 1083-1089.

[3] Pieczarka, Maciej, et al. "Bose–Einstein condensation of photons in a vertical-cavity surface-emitting laser." Nature Photonics 18.10 (2024): 1090-1096.

Quantum control of a single H2+ molecular ion

Idan Hochner

H2+ is the simplest stable molecule, and its internal structure is calculable to high precision from first principles. This allows tests of theoretical models and the determination of fundamental constants. However, studying H2+ experimentally presents significant challenges. In this preprint, the authors demonstrate full quantum control of a single H2+ molecule by using Quantum Logic Spectroscopy techniques. This work is the first to fully control a diatomic homonuclear molecule, paving the way toward precision measurements of these molecules. I will provide an overview of the motivation for studying diatomic molecules, the experimental challenges involved, and the innovative solutions that enabled the authors to overcome these obstacles.

[1 ]Holzapfel et al, arXiv:2409.06495

Building blocks for nanoscale magnetic resonance imaging

Telling apart two spins in a single molecule is a daunting task, and yet this is precisely the goal of nanoscale magnetic resonance imaging (nanoMRI), with the aim of determining structure, function and dynamics. In this talk I will first outline the potential benefits of this capability, from fundamental physics to drug discovery. Then, I will describe the overarching scientific dogma of my research group, making use of a quantum emitter in the form of the nitrogen-vacancy center in diamond as its central sensor. Finally, I will describe our work on the building blocks necessary to achieve our nanoMRI aim. These span magnetic tomography of electron spins with sub-angstrom precision, Bayesian inference for a boost in acquisition time and strong driving of nuclear spins going beyond the rotating frame approximation.

Journal club

All Optical Compton Scattering

Aaron Rafael Liberman

Extreme light-matter interactions promise to provide a new tool for testing quantum electrodynamics (QED) in the strong field regime and searching for new physics. One of the first interactions to study is non-linear inverse Compton scattering, in which a highly relativistic electron beam interactions with an intense laser pulse.

In this work, the authors present results from an all optical Compton scattering experiment, colliding laser-plasma accelerated electrons with a multi-petawatt laser system. They successfully show highly non-linear inverse Compton scattering, in which electrons scatter off hundreds of laser photons and produce gamma rays. This work provides a strong proof-of-concept for future explorations of the standard model and beyond.

[1] Mirzaie et al, "All-optical nonlinear Compton scattering performed with a multi-petawatt laser," Nature Photonics, 18, 1212–1217 (2024). https://doi.org/10.1038/s41566-024-01550-8

How Many Qubits Does It Take to Build a Superradiant Death Star?

Nikita Leppenen

Collective photon emission from a bunch of atoms is a fundamental problem with many applications, from quantum information technologies to quantum metrology and lasing. In this talk, I will discuss the universal scaling of the maximal decay rate with the number of two-level atoms in the ordered 3D, 2D, and 1D atomic arrays. Interestingly, except for the various applications, this problem also connects with the Hamiltonian complexity theory and has been shown to be a QMA-complete problem (hard to solve even on a quantum computer) [1]. Despite the inherent complexity, we will aim to interpret the results using physical intuition and matrix diagonalization. 
 

[1] W.-K. Mok, A. Poddar, E. Sierra, C. C. Rusconi, J. Preskill, and A. Asenjo-Garcia, Universal scaling laws for correlated decay of many-body quantum systems (2024), arXiv:2406.00722.

Journal club

Exploring the Kibble-Zurek Mechanism in Ultracold Gases

Gavriel Fleurov

The Kibble-Zurek mechanism (KZM) describes how topological defects form when a system rapidly crosses a phase transition. As the system nears the critical point, critical slowing down prevents it from maintaining uniform order, leading to independently ordered domains. The defects at the interfaces of these domains are remnants of the original symmetries. Initially developed to explain cosmic strings, KZM also applies to superfluids – such as in helium and ultracold atoms.

In this talk, I will discuss a recent observation of the KZM in a fermionic superfluid [1], where the authors applied a temperature and temporal quench and found evidence of scale invariance. Furthermore, I will briefly review other works on this topic [2,3].

[1] K. Lee, S. Kim, T. Kim, and Y. Shin, 10.1038/s41567-024-02592-z

[2] J. Beugnon and N. Navon, 10.1088/1361-6455/50/2/022002

[3] D. G. Allman, P. Sabharwal, and K. C. Wright, 10.1103/PhysRevA.109.053320

 Sub-cycle control of terahertz high-harmonic generation by dynamical Bloch oscillations

Roni Weiss

Ultrafast charge transport in strongly biased semiconductors is at the heart of high-speed electronics, electro-optics and fundamental solid-state physics. Intense light pulses in the terahertz spectral range have opened fascinating vistas. Because terahertz photon energies are far below typical electronic interband resonances, a stable electromagnetic waveform may serve as a precisely adjustable bias. Novel quantum phenomena have been anticipated for terahertz amplitudes, reaching atomic field strengths. We exploit controlled (multi-)terahertz waveforms with peak fields of 72 MV cm−1 to drive coherent interband polarization combined with dynamical Bloch oscillations in semiconducting gallium selenide. These dynamics entail the emission of phase-stable high-harmonic transients, covering the entire terahertz-to-visible spectral domain between 0.1 and 675 THz. Quantum interference of different ionization paths of accelerated charge carriers is controlled via the waveform of the driving field and explained by a quantum theory of inter- and intraband dynamics. Our results pave the way towards all-coherent terahertz-rate electronics.

[1] O. Schubert, M. Hohenleutner, F. Langer, B. Urbanek, C. Lange, U. Huttner, D. Golde, T. Meier, M. Kira, S. W. Koch, and R. Huber, 10.1038/nphoton.2013.349
 

Ideal sensing of entanglement by stimulation of the disentangling nonlinear interaction

Entanglement is a cornerstone of quantum science and technology, ranging the realms of quantum computing, metrology, communication and sensing. Generation of entanglement fundamentally requires a nonlinear interaction between the entangled parties: For example, time-energy entangled photon pairs are generated via nonlinear parametric down-conversion, leading to non-classical correlations in both time-difference (t1 − t2) and energy-sum (E1 + E2).

Standard techniques to detect and quantify entanglement rely on independent measurements of the entangled particles, followed by an evaluation of the correlations between them in post-processing. This indirect approach provides only partial information of the entanglement, since only one correlated degree of freedom can be evaluated. In the example of time-energy entanglement, either (t1 − t2) or (E1 + E2) can be deduced, but not both, due to the non-commuting nature of energy and time.

Ideally, if an entanglement sensor could measure only the combined observables that show correlation - (t1 − t2) and (E1 + E2) without measuring individual energies or times, the complete entanglement information could be recovered in a single shot. Conceptually, such a measurement can be performed using the reverse (disentangling) nonlinear interaction, i.e sum frequency generation (SFG), but such nonlinear interactions at the single-photon level are ridiculously inefficient.

I will present a method to overcome this fundamental barrier by stimulating the nonlinear SFG interaction with a strong pump. I will describe our experimental demonstration of efficient SFG detection for extremely broadband time-energy entangled bi-photons (octave-spanning energy spectrum of >120 THz and a correlated time-diff of ∼8fs). Measuring the spectrum of the SFG allowed us to observe the energy-sum distribution, while sweeping the relative delay/dispersion of the bi-photons provided the time-diff correlation at the same time, thereby uncovering the complete information of entanglement.

Weak and Strong Optical Turbulence.

I describe the new theory of far-from-equilibrium states of light in focusing and defocusing media.

PhD defense: A search of quantum signatures in ultracold Rb-Sr+ collisions

A hybrid system combining ultracold atoms and ions can be used to study collisions between a single pair of particles in the ultracold regime. In this talk, I will present recent observations of interactions between Sr+ ions and Rb atoms in the ultracold regime. Although formation of bound states is not expected in elastic two-body collisions due to energy and momentum conservation, trap-assisted bound states are formed [1]. We observed deviations in the cross-section attributed to these trap-assisted bound states. Numerical observation suggests that these bound states have chaotic properties [2], which might lead to signatures of quantum chaos. These findings offer insights into ultracold atom-ion collisions under trapping forces, potentially enabling precise control of interactions and exploration of quantum chaotic phenomena.

[1] Pinkas, M., Katz, O., Wengrowicz, J., Akerman, N. & Ozeri, R. Trap-assisted formation of atom–ion bound states. Nat. Phys. 19 (2023).
[2] Pinkas, M., Wengrowicz, J., Akerman, N. & Ozeri, R. Chaotic scattering in ultracold atom-ion collisions. arXiv:2401.18003 (2024).

Quantum advantage with classical data: Beyond time complexity

Will large quantum computers be useful for processing classical data, particularly in the regimes that are relevant for machine learning? This is still for the most part an open question. I'll make the case that it might be promising to search for quantum advantage beyond speedups and present results along these lines. The first is an unconditional, exponential advantage in communication for inference and gradient estimation with a distributed, parameterized quantum circuit. Additionally, we show that this advantage applies to circuits that resemble classical neural networks used to compute over graph data, and perform well on standard benchmarks. I’ll also discuss how encoding classical data in the amplitudes of a quantum state can provably prevent it from being re-used for computation without requiring cryptographic primitives or computational assumptions. This suggests that distributed quantum computation can improve the privacy of user data, and has potentially interesting economic implications that can be demonstrated in strategic data selling games.

Joint work with Hagay Michaeli, Siddhartha Jain, Daniel Soudry and Jarrod McClean.

PhD defense: Investigating multiexciton dynamics in semiconductor nanocrystals using temporal, spatial, and spectral photon correlations

The 2023 Nobel prize in Chemistry for the synthesis and spectroscopy of semiconductor nanocrystals (“quantum dots”) gave renewed validity to the widespread research done for more than 40 years and emphasized their major contribution to our lives, being at the forefront of fundamental research and development of optoelectronic applications. As charge carrier dynamics are of high importance for some applications, a detailed investigation of fundamental photophysics of quantum dots is a crucial step for designing quantum dot-based technologies. 
Unlike atoms, quantum dots have the unique capability to populate few excitons, bound electron-hole pairs, within a single excitation cycle, giving rise to multiexcitons and associated many-body interactions. Spectroscopy of quantum dots using ensemble techniques has been widely used to indirectly characterize the second and third excited states (biexciton and triexciton), yielding ambiguous results. 
My thesis focuses on the direct probing of multiexciton interactions in single semiconductor nanocrystals using photon correlation measurements as a spectroscopic tool. I will demonstrate a few detection schemes involving sophisticated single-photon avalanche diode (SPAD) array detectors that enable resolving higher excited states (such as the biexciton and triexciton) in the temporal, spatial, and spectral domains. In the first part I will show how higher-order temporal photon correlations reveal three-body interactions in nanoplatelets. In the second and third parts I will show how small changes in the dipole emission pattern and spectrum among the singly, doubly, and triply excited states can be discerned and teach us about the nature of excitonic interactions in the materials studied.
Altogether, the methods and insights gained in this research may contribute to the understanding of the underlying photophysics of semiconductor nanocrystals, being a scaffold for future experiments with other material systems. 
 

[1] D. Amgar, G. Yang, R. Tenne, D. Oron. Higher-Order Photon Correlation as a Tool to Study Exciton Dynamics in Quasi-2D Nanoplatelets. Nano Lett. 2019, 19, 8741.

[2] D. Amgar, G. Lubin, G. Yang, F. T. Rabouw, D. Oron. Resolving the Emission Transition Dipole Moments of Single Doubly Excited Seeded Nanorods via Heralded Defocused Imaging. Nano Lett. 2023, 23, 5417.
 

Quantum-secure multiparty deep learning

The demand for cloud-based deep learning has intensified the need for practical and readily deployable secure multiparty computation. In this talk, I will present a linear algebra engine that leverages the quantum nature of light for provably secure computation using simple, standard telecom components. Applied to deep learning, our approach achieves over 96% accuracy on the MNIST classification task while limiting information leakage to 0.1 bits per symbol

[1] Sulimany et al., arXiv:2408.05629 (2024).

PhD defense: Measuring Interactions in a Bosonic Mixture

Interactions in ultracold atomic mixtures are critical for understanding and harnessing complex quantum phenomena. These interactions, ranging from mean-field effects to more intricate schemes like dipole-dipole interactions and quantum fluctuations, are foundational in creating novel quantum states and behaviors. The ability to control and manipulate these interactions has profound implications for quantum technologies, including quantum computing, quantum sensing, and precision measurements. Fine-tuning these interactions makes it possible to engineer quantum systems with properties tailored for specific applications, pushing the boundaries of what can be achieved in fundamental and applied physics.

I will show two key aspects of these interactions. The first aspect is nonlinear spin dynamics within spin mixtures, which lead to phenomena such as spin squeezing and quantum phase magnification. These effects significantly enhance measurement precision and sensitivity, making them valuable for quantum sensing and information processing, where accuracy and coherence are paramount.

The second aspect is the interaction between atoms and their trapping potential, which is leveraged to develop a novel technique for measuring the gravitational mass of ultracold atoms. Inspired by recent advancements in antimatter research at CERN, this method offers a new approach to gravity measurements, with potential implications for precision measurement and fundamental physics.

Together, these studies underscore the importance of interactions in ultracold atomic systems and their far-reaching implications for advancing quantum technologies and our understanding of the quantum world.

[1] Observation of nonlinear spin dynamics and squeezing in a BEC using dynamic decoupling H Edri, B Raz, G Fleurov, R Ozeri, N Davidson New journal of physics 23 (5), 053005

[2] A new technique to measure gravitational mass of ultra-cold matter and its implications for antimatter studies B Raz, G Fleurov, R Holtzman, N Davidson, E Sarid arXiv preprint arXiv:

PhD Defense

Asymmetric Effects in Shock Injection for Laser-Plasma Electron Acceleration

Abstract: Laser-plasma acceleration (LPA), using plasma waves as a medium for transferring energy from an ultra-intense laser pulse to directional kinetic energy of electrons, is a promising candidate for the next generation of particle accelerators, capable of reaching the same energies at less than 0.1% acceleration length compared to classical RF-cavity based accelerators, thanks to the plasma medium's support of extremely large fields. LPA-based multi-GeV electrons [1] and LPA-based free electron lasers [2] have already been demonstrated, and LPA-based medical accelerators for oncological particle therapy are at the focus of interest of many research groups and commercial companies in academia and industry. However, one drawback of current laser-plasma accelerators is their beam quality, notably affected by the process of trapping and injection of ambient electrons into the in-plasma accelerating structure – a process whose improved understanding and development will unlock many other potential uses for these compact accelerators. In my research, the femtosecond relativistic electron microscopy (FREM) method [3], a technique significantly developed in our lab, has been used to probe the highly nonlinear dynamics of one of the most common injection implementations, razor-blade shock injection [4]. We have discovered that the tilt of the generated shock can induce transverse oscillations in the injected electrons until a part of the accelerated bunch splits out of the accelerating structure and drives its own plasma wave. This phenomenon, never reported before, was investigated and characterized, and our hope is that the insights gained by this research will contribute to the improvement of the injection process, and consequently to the overall quality of LPA-based electron beams, enabling this technology to fulfill the promise it holds for so many fields in our lives.

[1] A. J. Gonsalves et al. Petawatt Laser Guiding and Electron Beam Acceleration to 8 GeV in a Laser-Heated Capillary Discharge Waveguide. Phys. Rev. Lett. 122 084801 (2019).

[2] Marie Labat et al. Seeded free-electron laser driven by a compact laser plasma accelerator. Nature Photonics 17 150-156 (2023).

[3] Yang Wan, Sheroy Tata, Omri Seemann, Eitan Y. Levine, Slava Smartsev, Eyal Kroupp, and Victor Malka. Femtosecond electron microscopy of relativistic electron bunches. Light: Science & Applications 12 116 (2023).

[4] K. Schmid et al. Density-transition based electron injector for laser driven wakefield accelerators. Phys. Rev. ST Accel. Beams 13 091301 (2010).

High speed spatial light modulators for quantum control

The ability to control and program light is fundamental to science and technology, shaping a vast array of
fields from optical communications and microscopy, sensing, and astronomy. For some fields, the slow
devices commercially available today, known as spatial light modulators, are a core bottleneck for mature
systems – such as 3D holography, imaging through scattering media, and quantum computing.
Motivated by quantum control applications, where atomic or solid state atom-like qubits require high
speed addressing in hundreds of sites, and where photonic quantum computing has been explored using
spatial modes that require millions of degrees of freedom, I explore the development of high speed spatial
light modulators: devices that can control many spatial degrees of freedom of light at high speeds. In this
talk I discuss three different platforms that achieve this, each of which offers new advancements and
insights: First, a nanophotonic plasmonic modulator with liquid crystals fabricated in a “fabless” bulk
CMOS process[1] which can potentially democratize nanophotonics research, as well as allow for
multi-layer structures, scalability and electronic integration. Second, a Lithium Niobite on Silicon
device[2], where thin film LN with a guided mode resonance is bonded to a commercial CMOS
backplane, allowing for GHz speed modulation arising from the Pockels effect. Finally, a photonic crystal
array using specially designed photonic crystal cavities[3], working at ~0.2 GHz. With 64-100 pixels, this
demonstration is one of the largest scale foundry made devices ever made. The automated ‘holographic
trimming’ achieved a record picometre precision alignment of the cavity resonance for 81 devices.
These works pave the way for programmable control of millions of degrees of freedom of light at high
rates.
 

Journal club

Predicting many properties of a quantum system from very few measurements - Felix Ribout-Hirsh

I will present the groundbreaking work of Robert Hsin-Yuan Huang, Kueng and Preskill on shadow tomography that ultimately lead to Professor Preskill recent Bell Prize award in 2024. In order to realize the promise of Quantum Computing advantage, efficient read-out techniques of complex systems associated with Hilbert space of huge dimensionality are required. Classical shadow provides such method for constructing an approximate classical description of a quantum state using very few measurements of the state. Even more, this new approach lead to the opening of a new quantum-classical interface perspective, where different approaches to learning, both quantum or neural-network based, intertwine to create a new powerful paradigm. Finally I will review Robert Huang most recent tour-de-force work, where the impossible seems to become possible by « Certifying almost all quantum states with few single-qubit measurements ».

Improving quantum metrology beyond the NOON state - Michael Kali 

 In the talk, an overview of the field of quantum metrology will be given, focusing on phase estimation techniques.

The talk will then delve into the problem of multiple phases estimation – where quantum states can take advantage of the abundance of measured phases, to increase sensitivity.

Computer vision beyond conventional imaging

Abstract: Computer vision aims to endow machines with the ability to understand the environment through images and videos. It has made great progress in the past decade due to the combination of large datasets, novel architectures, and powerful computing. While the architectures and computing have changed dramatically over time, most vision algorithms still train on images captured with 'conventional' imaging, limiting the type of information that can be extracted about the environment. This talk will overview several works that expand computer vision by combining novel imaging hardware with task-specific physics-based inverse problems to reveal hidden phenomena.

First, I will describe the ACam - a camera designed to capture the minute flicker of artificial lights ubiquitous in our modern environments. I will show that bulb flicker is a powerful visual cue that enables various applications like scene light source unmixing, reflection separation, and remote analyses of the electric grid itself. Then, I will describe Diffraction Line Imaging, a novel imaging principle that exploits diffractive optics to capture sparse 2D scenes with 1D (line) sensors. The method's applications include fast motion capture, PIV, and structured light 3D scanning. I will also present a new approach for sensing minute high-frequency surface vibrations (up to 63kHz) for multiple scene sources simultaneously, using "slow" sensors rated for only 130Hz. Applications include capturing vibration caused by audio sources (e.g., speakers, human voice, and musical instruments) and localizing vibration sources (e.g., the position of a knock on the door). Lastly, I will present a novel active vision system that combines thermal imaging with laser illumination to enable dynamic vision tasks like object tracking, structure from motion, and optical flow on completely textureless objects.

Journal club (Wednesday)

Laser-guided lightning (Haim Nakav)

Lightning discharges between charged clouds and the Earth’s surface are responsible for considerable damages and casualties. It is therefore important to develop better protection methods in addition to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments—formed in the sky by short and intense laser pulses—can guide lightning discharges over considerable distances. We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Säntis mountain in north-eastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very-high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers. This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures.

Spin squeezing of atoms ensemble by prediction and retrodiction measurements (Elron Goldemberg)

The measurement sensitivity of quantum probes using N uncorrelated particles is restricted by the standard quantum limit, which is proportional to 1/ square root of N. This limit, however, can be overcome by exploiting quantum entangled states, such as spin-squeezed states. Here we report the measurement-based generation of a quantum state that exceeds the standard quantum limit for probing the collective spin of 10^11 rubidium atoms contained in a macroscopic vapor cell. . Achieved through stroboscopic quantum non-demolition measurements, our approach leverages past quantum states to extract spin information from earlier and later measurements. This methodology achieves a noise reduction equivalent to 5.6 decibels and metrologically relevant squeezing of 4.5 decibels compared to coherent spin states. The past quantum state yields tighter constraints on the spin component than those obtained by conventional QND measurements. This work could benefit practical applications in quantum metrology and parameter estimation, as demonstrated by its successful application to quantum-enhanced atomic magnetometry.

Joint Design of Optics and Post-Processing Algorithms Based on Deep Learning

Abstract: After the tremendous success of deep learning (DL) for image processing and computer vision applications, these days almost every signal processing task is analyzed using such tools. In the presented work, the DL design revolution is brought one step deeper, into the optical image formation process. By considering the lens as an analog signal processor of the incoming optical wavefront (originating from the scene), the optics is modeled as an additional “layer” in a DL model, and its parameters are optimized jointly with the “conventional” DL layers, end-to-end. This design scheme allows the introduction of unique feature encoding in the intermediate optical image, since the lens “has access” to information that is lost in conventional 2D imaging. Therefore, such design allows a holistic design of the entire IP/CV system.

The proposed design approach will be presented with several applications: text guided image acquisition and reconstruction, an extended Depth-Of-Field (DOF) camera; a passive depth estimation solution based on a single image from a single camera; non-uniform motion deblurring; video from a blurred image; and enhanced stereo camera with extended dynamic range and self-calibration abilities. This is a joint work with Erez Yosef, Shay Elmalem, Harel Haim, Yotam Gil Alex Bronstein, and Emanuel Marom

PhD Defense

Atom-mediated deterministic photonic graph state generation

Abstract:

Highly-entangled multi-photon graph states are a crucial resource in photonic quantum computation and communication. Yet, the lack of photon-photon interactions makes the construction of such graph states especially challenging. Typically, these states are produced through probabilistic single-photon sources and linear-optics entangling operations that require indistinguishable photons. The resulting inefficiency of these methods necessitates a large overhead in the number of sources and operations, creating a major bottleneck in the photonic approach. Here, I will show how harnessing single-atom-based photonic operations can enable deterministic generation of photonic graph states, while also lifting the requirement for photon indistinguishability. To this end, I will introduce a multi-gate quantum node comprised of a single atom in a W-type level scheme coupled to an optical resonator. This configuration provides a versatile toolbox for generating graph states, allowing the operation of two fundamental photon-atom gates, SWAP and controlled-Z, as well as the deterministic generation of single photons.

PhD Defense

Nanoscale magnetic resonance techniques based on the nitrogenvacancy center in diamond

Abstract:

Magnetic resonance techniques constitute a powerful toolbox with a vast impact on
the natural sciences. Contemporary techniques, however, only assess large material
ensembles, obscuring single-molecule details. The nitrogen-vacancy (NV) center, a
point defect of the diamond crystal, can function as a quantum sensor capable of
detecting minute fields in nanoscale volumes. Quantum sensing with NV centers is
thus a promising approach toward single-molecule magnetic resonance. Here, I
present progress on nanoscale magnetic resonance techniques using NV centers.
I will introduce the magnetic tomography method that maps the position of single
electron spins with Angstrom-level precision and discuss its potential application to
single-molecule distance measurements. Additionally, I will show results from
experiments on rapid nuclear spin manipulation, achieving unprecedented
manipulation rates. Optimized for NV center experiments, the technique may apply
to other spin qubit platforms. In this context, I introduce a novel approach for
enhancing pulse fidelity in the strong driving regime.
These results advance the capability of NV centers in nanoscale magnetic resonance,
particularly toward the goal of single-molecule distance measurements.
 

Journal club

First Electron Acceleration with an Axiparabola

Abstract:

The axiparabola, a long-focal-depth reflective optical element that produces a quasi-Bessel beam [1], has generated interest in its potential to both overcome the beam diffraction and electron dephasing limitations of laser-wakefield acceleration [2,3]. The former is accomplished by the diffraction-free propagation properties of the Bessel beam while the later through a combination of the dynamics imposed by the axiparabola itself and a manipulation of the spatio-temporal profile of the incoming beam [2,3]. Here, we demonstrate a proof-of-concept result: the first acceleration of electrons using an axiparabola-focused wakefield, combined with a system for manipulation of the laser beam’s spatio-temporal shape. We also show experimental measurements of the axial energy deposition velocity of the axiparabola and the ability to tune this velocity profile [4]. This proof-of-concept experiment shows the feasibility of using the axiparabola and presents a roadmap for further optimization towards the eventual goal of dephasingless laser-wakefield acceleration.

[1] S. Smartsev et al. “Axiparabola: a long-focal-depth, high-resolution mirror for broadband high-intensity lasers,” Optics Letters 44, 3414-3417 (2019)

[2] C. Caizergues et al. “Phase-locked laser-wakefield electron acceleration,” Nature Photonics 14, 475-479 (2020)

[3] J.P. Palastro et al. “Dephasingless Laser Wakefield Acceleration,” PRL 124, 134802 (2020)

[4] Liberman et al. “Use of spatiotemporal couplings and an axiparabola to control the velocity of peak intensity.” Optics Letters 49, 814-817 (2024)

Journal club

• Demonstrating a long-coherence dual-rail erasure qubit using tunable transmons (Ofir Milul) 

Quantum error correction with erasure qubits promises significant advantages over standard error correction due to favorable thresholds for erasure errors. To realize this advantage in practice requires a qubit for which nearly all errors are such erasure errors, and the ability to check for erasure errors without dephasing the qubit. We
demonstrate that a “dual-rail qubit” consisting of a pair of resonantly coupled transmons can form a highly coherent erasure qubit, where transmon T1 errors are
converted into erasure errors and residual dephasing is strongly suppressed, leading to millisecond-scale coherence within the qubit subspace. We further demonstrate midcircuit detection of erasure errors while introducing < 0.1% dephasing error per check.Finally, we show that the suppression of transmon noise allows this dual-rail qubit to preserve high coherence over a broad tunable operating range, offering an improved capacity to avoid frequency collisions

• Laser Excitation of the Th-229 Nucleus (Dror Einav)

  The ability to excite elementary quantum systems using lasers cannot be overestimated and is at the heart of many experiments and technologies like spectroscopy, atomic clocks, quantum information processing, etc. For the first time, resonant excitation was successfully implemented to excite an atom nucleus, taking advantage of the unusual low-energy transition of the Th-229 nucleus. This opens doors for nuclear-based experiments and technologies. I will give an overview of the past efforts to achieve this goal and of the novel results.

Harnessing coherent control of tunneling: Spatial adiabatic passage and atomic interferometry with ultracold atoms in optical tweezers

Abstract:

Optical tweezers can trap and manipulate single atoms, offering significant potential for advancing technologies in quantum computation, simulation, and sensing. Recently, we have developed a new tweezer array apparatus focused on using fermionic atoms and harnessing tunneling for quantum logic and wave-packet control. In this talk, I will present an experiment demonstrating spatial adiabatic transport of atoms across three tweezers through precise control of coherent tunneling. I will explain how such adiabatic processes can be generalized to implement topological pumps and atomic beam splitters, the latter being key elements in atomic interferometry. Furthermore, I will propose a new guided atomic interferometry technique based on optical tweezers, which allows for extended probing times, sub-micrometer positioning accuracy, and increased flexibility in shaping atomic trajectories. Using fermionic atoms offers the advantages of achieving single-atom occupation of vibrational states and reducing mean-field shifts. I will discuss two applications ideally suited for the unique capabilities of the tweezer interferometer: measuring gravitational forces and studying Casimir-Polder forces between atoms and surfaces. Finally, I will explain how tweezer-based atomic interferometry can be extended to perform clock interferometry, potentially testing the quantum twin paradox and examining quantum coherence in the context of gravitational time dilation for the first time.

Journal club

• Realizing a quantum memory via Majorana zero-modes on a trapped ions system (Jovan Markov)

Abstract:  

Finding a qubit that is free from decoherence is a significant challenge in quantum computing. Systems that are protected topologically provide promising characteristics for constructing a fault tolerant quantum memory. Nonetheless, the actual implementation of topological quantum memories remains a difficult issue to solve. One of the simplest models that hones topological phases is the Kitaev chain which is a 1D chain of fermions of the same spin [1]. There has been a proposal how to encode a topologically protected qubit using Majorana fermions in a trapped-ions chain [2]. In this talk I will present this proposal and explain how can we realize a quantum memory via Majorana zero modes in a trapped-ions system by using Hamiltonian-engineering techniques developed in our lab.

[1] Unpaired Majorana fermions in quantum wires, Kitaev A Y 2001 Phys.—Usp. 44 131

[2] Topological Qubits with Majorana Fermions in Trapped Ions, A Mezzacapo et al., New Journal of Physics 15 (2013) 033005.

• Direct observation and spectroscopy of three-photon cascaded emission from triexcitons in giant CsPbBr3 QDs (Dekel Nakar)

Abstract: We study the spectroscopy and kinetics of three-photon cascaded emission from triexcitons in giant CsPbBr3 quantum dots using heralded spectroscopy. Although their
second-order correlation function is near unity, we identify single emitters by a monoexponential radiative decay curve for each step of the cascade, proving the emission is the result of a single multiexciton emission cascade. We then study the spectral and kinetic properties of this emission. Conceptually, generating higher-order multiexcitons can lead to states of quantum-correlated photons with more than two photons for possible use in quantum computation.
 

Journal club

• Collective radiation beyond Dicke model: breakdown of steady-state superradiance (Nikita Leppenen)

Abstract: rogressive enhancements in producing dense and/or arranged ensembles of atoms in free space have generated interest in studying their collective radiational properties. Superradiance — the enhancement of N^2 in the radiated power from the system, theoretically captured by the Dicke model for the transient pulse from the ensemble of indistinguishable atoms — could also be revealed in the steady state of a setup where such a system radiates light under a constant external laser drive. However, for any realistic system, individual-level dissipation channels break the indistinguishability of the atoms, influencing superradiance phenomena. In this talk, I will motivate and review recent theoretical advances in the study of collective radiation beyond the Dicke model [1,2].

[1] S. Ostermann, O. Rubies-Bigorda, V. Zhang, and S. F. Yelin, Breakdown of steady-state superradiance in extended driven atomic arrays (2023), arXiv:2311.10824
[2] N. Leppenen and E. Shahmoon, Quantum bistability at the interplay between collective and individual decay (2024), arXiv:2404.02134

• Self-Induced Superradiant Masing (Yoav Shimshi)

Abstract: We study superradiant masing in a hybrid system composed of nitrogen-vacancy center spins in diamond coupled to a superconducting microwave cavity. After the first fast superradiant decay we observe transient pulsed and then quasi-continuous masing. This emission dynamics can be described by a phenomenological model incorporating
the transfer of inverted spin excitations into the superradiant window of spins resonant with the cavity. After experimentally excluding cQED effects associated with the pumping of the masing transition we conjecture that direct higher-order spin-spin interactions are responsible for creating the dynamics and the transition to the sustained masing. Our experiment thus opens up a novel way to explore many-body physics in disordered systems through cQED and superradiance.

Journal club

• Complex Berry phase under the tunneling barrier (lior Faeyrman)

Abstract: Will an electron traversing the tunneling barrier feel the geometric properties of a material inside the classically-forbidden region? We introduce the
manifestation of a complex geometric phase accumulated by an electron wavepacket during the tunneling mechanism in solid-state systems. We
experimentally resolve this phase by inducing an internal interferometer, composed of two electrons trajectories, while resolving their relative
complex phase via high harmonic generation atto-second spectroscopy.

[1] M.Berry, A. Mathematical and Physical Sciences 392, 45-57 (1984)
[2] A. Uzan-Narovlansky, L. Faeyrman, et al. Nature 626, 66–71 (2024)

• Playing with dice for fun and privacy (Noam Cohen-Avidan)

Abstract: We know that the nature of quantum mechanics is random. Some people do not like this fact. In this talk, I will take the other point of view and present
how randomness can be useful. I will present the cryptographic perspective on randomness as a valuable resource. I will start by explaining how
randomness is essential for keeping secrets. Next, I will introduce more advanced cryptographic concepts, such as zero-knowledge proofs,
commitments, and secret sharing, and show how they rely on randomness. The goal is to introduce the audience to basic concepts in cryptography and
explain why randomness is desirable.

Journal club

One-Way Hashing Method with Finite Resources (Thomas Hahn)

Abstract: The one-way hashing method refers to a well-known entanglement distillation protocol that can be used to transform multiple copies of a bipartite state into high fidelity Bell pairs, using only local operations and classical communication. While it is known that this protocol is very effective at distilling entanglement from large-scale systems, previous results indicated that the one-way hashing method may not be useful when the number of initial copies is small. For this reason, the protocol has not yet been realized by any experimental setup. By leveraging properties of the Hartley entropy, we provide significantly improved analytical lower bounds on this protocol's distillation rate, as well as numerical simulations, which demonstrate that entanglement can be distilled via the one-way hashing method at a higher rate and using fewer initial copies than previously expected. These results show that the one-way hashing method is not only of interest for future large-scale quantum networks; it is also a viable option for distilling entanglement on state-of-the-art quantum technologies.

High Interharmonic Generation from Isolated Bound States (Sergey Hazanov)

Abstract: High harmonic generation (HHG) is a nonlinear process in which systems driven by intense laser emit integer harmonics of the driving field. Here we report that the strong nonlinear response of systems with isolated bound states split the HHG spectrum into non-harmonic Mollow-type triplets that reveal the internal electronic dynamics. We identify the conditions required to observe these phenomena and propose potential experimental systems that could enable their detection. Our findings offer new insights into the fundamental physics of HHG and may have applications in high-harmonic spectroscopy, X-ray physics and study of ultrafast dynamics.

High-dimensional quantum information processing using spatially entangled photons

High-dimensional entanglement promises to boost the information capacity and resilience to noise of photonic quantum technologies. In this talk, I will focus on the spatial degree of freedom of photons and how it can be utilized for quantum information processing. I will describe our work on the scattering of quantum light in disordered media [1], including scattering compensation [2], Hanbury Brown Twiss (HBT) interference [3], and coherent backscattering [4] of entangled photons. I will then show our recent results on manipulating high-dimensional entanglement using multi-plane light conversion [5] for entanglement certification in large cluster states.

[1] Ohad Lib, and Yaron Bromberg. "Quantum light in complex media and its applications." Nature Physics 18.9 (2022)

[2] Ohad Lib Giora Hasson, and Yaron Bromberg. "Real-time shaping of entangled photons by classical control and feedback." Science Advances 6.37 (2020)

[3] Ohad Lib, and Yaron Bromberg. "Thermal biphotons." APL Photonics 7.3 (2022)

[4] Mamoon Safadi, Ohad Lib, et al. "Coherent backscattering of entangled photon pairs." Nature Physics 19.4 (2023)‏

[5] Ohad Lib, Kfir Sulimany, and Yaron Bromberg. "Processing entangled photons in high dimensions with a programmable light converter." Physical Review Applied 18.1 (2022)

Journal Club

• Non-destructive inelastic recoil spectroscopy of a single molecular ion (Orr Barnea)

A novel single molecule technique is demonstrated that is compatible with high precision measurements and obtained the spectrum of two molecular ion species. While the current result yields modest spectral resolution due to a broad light source, The method is expected to ultimately provide resolution comparable to quantum logic methods with significantly less stringent requirements. Adaptations of this technique will prove useful in a wide range of precision spectroscopy arenas including the search for parity violating effects in chiral molecules. I will present a qualitative comparison between this method and quantum logic spectroscopy and the tradeoff between them.

• Enhancing the lifetime of a superconducting cavity qubit through environment monitoring and feedback (Uri Goldblatt)

Bosonic qubits encoded in superconducting cavities are a promising approach for realizing quantum memories and bosonic codes with built-in protection against decoherence. However, a noisy ancilla qubit is required to encode and manipulate the bosonic qubit. As a result, ancilla errors propagate to the cavity, dephasing the cavity-encoded qubit. This error propagation presented a major limitation in previous experiments with bosonic qubits. I'll present a thorough review of this phenomenon as well as a novel error mitigation protocol based on repeated measurements and real-time feedback to suppress this error propagation. I'll demonstrate the effect of this procedure on the coherence time of the bosonic qubit.

Logical qubit quantum computing with neutral atom arrays

Useful quantum computing will likely require large quantum computers with very low error rates, potentially achievable with quantum error correction (QEC). In QEC, errors are suppressed by nonlocally encoding information on logical qubits. I’ll review our recent report on a programmable logical-qubit quantum processor based on reconfigurable neutral atom arrays [1]. We realize up to 48 logical qubits and hundreds of entangling gates, using up to 280 physical qubits, high gate fidelities [2], arbitrary connectivity, and parallel and arbitrary single-site control. We demonstrate fault-tolerant logical qubit preparation, a logical GHZ state preparation circuit and full state tomography, improvement of a two-qubit logic gate by scaling surface code distance (up to d=7), mid-circuit feed forward, and computationally complex circuits including many non-Clifford gates. We explore the latter via sampling and measurements of entanglement entropy. I’ll discuss our vision for large scale error-corrected quantum processors based on the key concepts of hardware-efficient transversal gates and a multi-zoned architecture, as well as the main challenges for further scaling. Time permitting, I’ll briefly touch on recent results in analog quantum simulation with atom arrays, including explorations of quantum coarsening and novel Hamiltonian engineering techniques. 

[1] Bluvstein et al. Nature (2023) 

[2] Evered et al. Nature (2023) 

Highly nonlinear ultrafast dynamics in liquids and quantum matter

High harmonic generation (HHG) is a nonlinear frequency up-conversion process that occurs when intense laser pulses irradiate matter. In gas-phase it has been extensively studied and is very well-understood (e.g. leading to the 2023 Physics Nobel Prize for attosecond science). In solids, research is ongoing, but a consensus is forming for the dominant HHG mechanisms. In liquids however, no established theoretical model for HHG exists, and the underlying chemical and physical mechanisms remain unidentified. Advancement on this front may lead to novel light sources, and are especially appealing for ultrafast spectroscopy of chemistry in solutions. I will present our recent efforts in tackling this problem with a combination of ab-initio calculations[1], semi-analytical models, and experimental data obtained by collaborators at ETHZ. I will show that HHG in liquids is strongly affected by the electronic mean-free-path, thus allowing its extraction from all-optical measurements, and demonstrating the first application of high harmonic spectroscopy in liquids[2]. I will also show that higher-order scattering processes play a central role in the higher-energy part of liquid-HHG. Lastly, I’ll discuss my recent works on high harmonic spectroscopy of topological phases of matter (challenging the current conception in the field that topology strongly affects solid HHG)[3], and on strong-field driving of attosecond magnetization dynamics in quantum materials, constituting the prediction for the fastest light-driven magnetization dynamics to date[4].

[1] Neufeld et al., JCTC 18, 4117 (2022). https://doi.org/10.1021/acs.jctc.2c00235.

[2] Mondal*, Neufeld* et al., Nat. Phys. (2023). https://doi.org/10.1038/s41567-023-02214-0. 

[3] Neufeld et al., PRX 13, 031011 (2023). https://doi.org/10.1103/PhysRevX.13.031011.

[4] Neufeld et al., npj Comp. Mat. 9, 39 (2023). https://doi.org/10.1038/s41524-023-00997-7.

Temperature dependent spectroscopy of colloidal nano-crystals and coherent image scanning CARS imaging

In this talk I will present our modest contribution in two branches of optical microscopy: a novel application of a spectroscopic technique in the study of semiconductor nano-crystals, and the development of a new non-linear microscopy scheme: phase-resolved, super-resolved CARS imaging.

Excitons in colloidal semiconductor nanoplatelets (NPLs) are weakly confined in the lateral dimensions. This results in significantly smaller Auger rates and, consequently, larger biexciton quantum yields, when compared to spherical quantum dots (QDs). Utilizing the cascaded nature of bi-excitonic emission to perform a time gated photon correlation experiment, we studied the temperature dependence of Auger and radiative rates in NPLs. We showed how using this method the Auger rate can be directly measured for single particles. We found that the Auger rate is largely temperature independent. This result support the claim that colloidal NPLs behave like two-dimensional quantum wells.

Technical advances made in the last two decades have pushed the boundary of the vibrational spectroscopic imaging field, and in particular Coherent Anti-stokes Raman Scattering (CARS) imaging, to a powerful tool for biological, medical and non-destructive applications. Separately, Image Scanning Microscopy (ISM) uses simple manipulation, namely pixel reassignment, to enhance the resolution of a confocal microscope without loss of signal. However, its application is predicated upon the signal being incoherent, as is the case for fluorescence. In order to adept this method to CARS imaging, we have designed and constructed a phase-resolved CARS microscope. Resolving the full field, we demonstrate super-resolved CARS imaging.

Benjamin, E., Yallapragada, V.J., Tenne, R., Amgar, D., Yang, G., Oron, D., 2020. Temperature

dependence of excitonic and biexcitonic decay rates in colloidal nanoplatelets

by time gated photon correlation. The Journal of Physical Chemistry Letters, 11 (16), pp.6513-6518.

Quantum imaging with free electrons and light

The ability to control and manipulate free electrons and light is interesting for its fundamental aspects, while its development for imaging applications has seen great progress, enabling imaging at increasing sensitivity and resolution. Recent developments in quantum information and quantum metrology have inspired a growing interest in developing techniques that manipulate free electrons and light for applications of quantum information processing, as well as to attain quantum limits in imaging applications. In the first part of the talk, I will focus on free electrons, where I will describe a technique to manipulate the transverse wavefunction of free electrons using thin photodiodes illuminated with patterned continuous wave light. These manipulations could in the future allow free-electron entanglement and quantum simulations using free electrons, as well as advanced applications of electron microscopy. [1] In the second part of the talk, I will present a classical technique to enhance the sensitivity and throughput of imaging a dynamic sample that approaches the quantum limit, surpassing sensitivity enhancement of all previous demonstrations of imaging that use squeezed light or entanglement. [2]

References:

[1] S. Koppell, Y. Israel, A. Bowman, B. Klopfer, M. Kasevich, Appl. Phys. Lett. 120, 190502 (2022)

[2] Y. Israel, L. Reynolds, B. Klopfer, M. Kasevich, Optica, 10, 491-496 (2023)

From Multimode Nonlinear Optics to High-Dimensional Quantum Communications

Quantum photonics often relies on nonlinear optics for the generation of photons, followed by reconfigurable linear optical networks for coherent control. In this talk, I will review our study of multimode nonlinear optics in fibers [1,2], which also enabled our realization of an all-fiber entangled photon pairs source [3]. These photons are spatially entangled in the eigenmodes of the multimode fiber, allowing for high-dimensional quantum communications. I will then present a couple of methods to coherently control such states. The first is achieved by multiplane light conversion based on a spatial light modulator [4], while the second is by employing a “Fiber piano” [5]; a piezo-actuator array that deforms the multimode fiber. Finally, I will introduce a novel Quantum Key Distribution protocol that utilizes high-dimensional encoding to boost the secure key rate and its experimental implementation [6].

[1] Kfir Sulimany, et al. Physical Review Letters 121.13 (2018): 133902.

[2] Kfir Sulimany, et al. Optica 9.11 (2022): 1260-1267.

[3] Kfir Sulimany, and Yaron Bromberg. npj Quantum Information 8.1 (2022): 1-5.

[4] Ohad Lib, Kfir Sulimany, and Yaron Bromberg. Physical Review Applied 18.1 (2022): 014063.

[5] Finkelstein, Zohar, Kfir Sulimany, et al. APL Photonics 8, no. 3 (2023).

[6] Kfir Sulimany, et al. arXiv preprint arXiv:2105.04733 (2021). Under review.

Generating complex entanglement in trapped-ions based quantum computers

Large, coherent, and well-controlled quantum computers are expected to have a tremendous effect on various computational fields such as material science, chemistry, medicine, infrastructure etc. Thus, a wide-ranging effort is taking place, involving many academic, industry and government participants, with the goal of constructing a useful quantum computer.

Our modest contribution to this global effort will be presented in the context of quantum computers that are based on electrically trapped linear crystals of atomic ions. Such quantum computers offer a unique property, namely a substantial and non-local coupling between all their constituent qubits, that stems from the long-range repulsive Coulomb interaction between the ions in the crystal.

This interaction can be controlled and shaped by driving the trapped ions with a fine-tuned multi-tone drive. We demonstrate, theoretically and experimentally, that such a control enables performing programmable, large scale and simultaneous logical operation on the trapped ions, as well as making these operations resilient to various sources of error and noise. Furthermore, we use spectral control to perform simulations of
quantum systems, that manifest geometries that do not necessarily conform to the linear geometry of the ion-crystal, and exhibit interactions between its constituent particles.
 

Zoom link:

https://weizmann.zoom.us/j/93287950378?pwd=WmVncU53eXRXR0Y3cWg3eklPQlBqZz09

Local dissipation effects in the driven-dissipative Dicke phase transition

The driven Dicke model, where an ensemble of atoms is driven by an external field and undergoes collective spontaneous emission through a leaky cavity mode, is a paradigmatic model that exhibits a driven-dissipative phase transition as a function of driving power. Recently, a highly analogous phase transition was experimentally observed, not in a cavity setting, but rather in a freespace atomic ensemble. Motivated by this, we present our ongoing efforts to better characterize the free-space problem, and understand possible differences compared to the cavity version. We specifically discuss a minimal model for the free space based on the Maxwell-Bloch equations. We find that the presence of local dissipation dramatically changes the properties of the phase transition. In particular, we present preliminary arguments that suggest that the free-space case might exhibit a smooth crossover rather than a true phase transition in the thermodynamic (large atom number) limit.

Communication with quantum circuits

The field of quantum communication involves sending quantum states from one location to another. This has potential applications in building secure communication channels through quantum cryptography as well as in sharing resources between quantum computers that are part of a quantum network. Quantum communication protocols based on multi-photon states can support greater transmitted information density than those relying on single photon states. Bidirectional communication would further increase channel efficiency, but this has not yet been achieved for multi-photon wavepackets at microwave frequencies. In this talk, I will present an experiment demonstrating bidirectional multi-photon transfers between two distant tunable resonators in a superconducting system, enabling single-pass on-demand transfers of photon superposition states.

Metamaterials of fluids of light and sound

Lattices of exciton polariton condensates represent a rich platform for the study and implementation of non-Hermitian non-linear bosonic quantum systems. Actuation with a time dependent drive provides the means, for example, to perform Floquet engineering, Landau-Zenner-Stückelberg state preparation, and to induce resonant inter-level transitions. With this perspective we introduce polaromechanical metamaterials, two-dimensional arrays of mm-size zero-dimensional traps confining light-matter polariton fluids and GHz phonons.

A strong exciton-mediated polariton-phonon interaction [1] can be exploited in these metamaterials, both using electrically injected bulk-acoustic waves [2] or self-induced coherent mechanical oscillations [3], to induce a time-dependence in the level energies and/or in the inter-site polariton coupling J(t). This has remarkable consequences for the dynamics. For example, when locally perturbed by continuous wave optical excitation, polariton condensates respond by locking the energy detuning between neighbor sites at multiples of the phonon energy [4]. We theoretically describe these observations in terms of synchronization phenomena involving the polariton and phonon fields. We study lattices of closely connected traps (defined by a linear optomechanical coupling), and also well separated t! raps (characterized by a quadratic optomechanical coupling), and discuss the role of dissipation and non-linearities in the stability of the observed asynchronous locking. The described metamaterials open the path for the study of non-reciprocal transport in dissipative quantum light fluids spatially and temporally modulated by GHz hypersound.

1. P. Sesin et al., Giant optomechanical coupling and dephasing protection with cavity exciton-polaritons, arXiv:2212.08269.
2. A. S. Kuznetsov et al., Electrically Driven Microcavity Exciton-Polariton Optomechanics at 20 GHz, Physical Review X 11, 021020 (2021).
3. D. L. Chafatinos et al., Polariton-Driven Phonon Laser, Nature Communications 11, 4552 (2020).
4. R D. L. Chafatinos et al., Asynchronous Locking in Metamaterials of Fluids of Light and Sound, arXiv:2112.00458, Nature Communications (in press).

Optical Multidimensional Coherent Spectroscopy

The concept of multidimensional coherent spectroscopy originated in NMR where it enabled the determination of molecular structure. The key concept is to correlate what happens during multiple time periods between pulses by taking a multidimensional Fourier transform. The presence of a correlation, which is manifest as an off-diagonal peak in the resulting multidimensional spectrum, indicates that the corresponding resonances are coupled. Migrating multidimensional Fourier transform spectroscopy to the optical regime is difficult because phases are critical. I will give an introduction to optical two-dimensional coherent spectroscopy, using an atomic vapor as a simple test system. I will then present our use of it to study optical resonances due to excitons in semiconductor nanostructures including transition metal dichalcogenides, where it is useful to incorporate laser-scanning microscopy.

Quantum computing with trapped ions

Quantum technologies allow for fully novel schemes of hybrid computing. We employ modern segmented ion traps. I will sketch architectures, the required trap technologies and fabrication methods, control electronics for quantum register reconfigurations, and recent improvements of qubit coherence and gate performance. Currently gate fidelities of 99.995% (single bit) and 99.8% (two bit) are reached. We are implementing a reconfigurable qubit register and have realized multi-qubit entanglement [1] and fault-tolerant syndrome readout [2] in view for topological quantum error correction [3] and realize user access to quantum computing [4]. The setup allows for mid-circuit measurements and real-time control of the algorithm. We are currently investigating various used cases, including variational quantum eigensolver approaches for chemistry or high energy relevant models, and measurement-based quantum computing. The fully equipped in house clean room facilities for selective laser etching of glass enables us to design and fabricate complex ion trap devices, in order to scale up the number of fully connected qubits. Also, we aim for improving on the speed of entanglement generation. The unique and exotic properties of ions in Rydberg states [5] are explored experimentally, staring with spectroscopy [6] of nS and nD states where states with principal quantum number n=65 are observed. The high polarizability [7] of such Rydberg ions should enable sub-µs gate times [8].

1. Kaufmann er al, Phys. Rev. Lett. 119, 150503 (2017)
2. Hilder, et al., Phys. Rev. X.12.011032 (2022)
3. Bermudez, et al, Phys. Rev. X 7, 041061 (2017)
4. https://iquan.physik.uni-mainz.de/
5. A. Mokhberi, M. Hennrich, F. Schmidt-Kaler, Trapped Rydberg ions: a new platform for quantum information processing, Advances In Atomic, Molecular, and Optical Physics, Academic Press, Ch. 4, 69 (2020), arXiv:2003.08891
6. Andrijauskas et al, Phys. Rev. Lett. 127, 203001 (2021)
7. Niederlander et al, NJP 25 033020 (2023)
8. Vogel et al,  Phys. Rev. Lett. 123, 153603 (2019)

Journal club

Collective shift in resonant light scattering by a one-dimensional atomic chain

We experimentally study resonant light scattering by a one-dimensional randomly filled chain of cold two-level atoms. By a local measurement of the light scattered along the chain, we observe constructive interferences in light-induced dipole-dipole interactions between the atoms. They lead to a shift of the collective resonance despite the average interatomic distance being larger than the wavelength of the light. This result demonstrates that strong collective effects can be enhanced by structuring the geometrical arrangement of the ensemble. We also explore the high intensity regime where atoms cannot be described classically. We compare our measurement to a mean-field, nonlinear coupled-dipole model accounting for the saturation of the response of a single atom.

Phys. Rev. Lett. 124, 253602 (2020)

Tomography of Feshbach Resonance States

Quantum phenomena that lead to the formation of long-lived collision complexes, such as scattering resonances, play a central role in the outcome of cold atomic and molecular collisions. These phenomena are fundamental probes of the fine details of internuclear interactions, and their understanding is crucial for future quantum technologies with cold molecules. In this talk, I will show a new method to populate and probe near-threshold Feshbach resonance states. In addition to the resonance energy, we obtain the state-to-state distribution of final scattering states, providing a tomographic picture of the resonance state [1]. Our method is based on the coincidence detection of electron/ion momenta in Penning ionization collisions between metastable noble gas atoms and neutral molecules/atoms [2]. We demonstrate our ability to filter out the resonance pathway from complex collision processes involving reactive, inelastic, and elastic pathways. We obtain several tens of quantum numbers per measurement without any laser detection schemes. We present an excellent match between theory and experiment, which allowed us to demonstrate a unique quantum signature of the resonance states on the final state distribution. In addition, we present an experimental scheme for control of the final state distribution, which is based on the initial constraint of total angular momentum at the Ionization step of the dynamics. The latter is motivated by our recent observation of a partial wave resonance at the lowest state of relative angular momentum [3].

1. Margulis B. et al, arXiv:2212.02828 (2022).
2. Margulis B. et al, Nature Communications, 11(1), 1-6 (2020). [3] Margulis B. et al, Physical Review Research, 4(4), 043042 (2022).

Quantum Information Processing with Light: from Single Photons to Continuous Variables

In this talk, I will present my journey moving from working with single photons to continuous variables. The signal-to-noise ratio (SNR) of range measurements can be improved by quantum detection and quantum light sources (quantum ranging). In the first part, I will present the theory of quantum ranging in the framework of Gaussian states. I will show that an optimal detection strategy, which minimizes the detection errors, can be applied for an arbitrary return state from the target. Then I will discuss the use of quantum light in the same scenario. Optimal detection is important in high-loss mediums, such as underwater, where low signal returns and maximizing its information is needed. In the second part, I will present experimental results of improved sensitivity of a temperature sensor and quantum simulations with single photons and will present my plans to extend the theory and experiments to Gaussian states. I will show simulations of a basic transition of quantum gravity theory and discuss scaling it up to complex transitions. Complex versions of these simulations have the potential to advance the research of basic science.

White-light holographic imaging using the optical coherence matrix formalism (or how to beat classical light-field imaging’s resolution limit)

Light-field cameras promised to revolutionize imaging by capturing and recording the propagation paths of light-rays through space. This light-field information, equivalent to canonical optical phase space, supposedly holds the “sys-admin” password to optical imaging. Digital post-processing and manipulation can allow digital refocusing of rays, correction of optical aberrations, as well as calculating the distance to every point in the imaged scene. However, once this technology was put into practice, its severe limitations and trade-offs became apparent. The main problem is that conventional light-field imaging contains an inherent trade-off between the light-rays’ angular information and the overall image resolution, analogous to Heisenberg’s uncertainty principle. PxE Holographic Imaging has developed a white-light holographic imaging camera that overcomes these limitations allowing highly accurate depth inference, digital refocusing and deblurring, as well as holographic, wavefront, and spectral imaging to be performed with no compromise on image resolution. In this talk we’ll explain the physics behind this breakthrough, and it’s relation to the optical coherence matrix formalism, the Wigner distribution, von Neumann measurements, and positive-operator-valued measures (POVMs).

Non-Thermal Pathways to the Origin of a Charge Density Wave

Highly correlated systems host in many cases a complex electronic phase diagram, with different phases competing or emerging from one-another. A new group of kagome metals AV3Sb5 (A = K, Rb, Cs) exhibit a variety of intertwined unconventional electronic phases, which emerge from a puzzling charge density wave phase. Understanding of this parent charge order phase is crucial for deciphering the entire phase diagram. However, the mechanism of the charge density wave is still controversial, and its primary source of fluctuations – the collective modes – have not been experimentally observed. In my talk I will show how we use ultrashort l! aser pulses to melt the charge order in CsV3Sb5 and record the resulting dynamics using femtosecond angle-resolved photoemission. We resolve the melting time of the charge order and directly observe its amplitude mode, imposing a fundamental limit for the fastest possible lattice rearrangement time. These observations together with ab-initio calculations provide clear evidence for a structural rather than electronic mechanism of the charge density wave, providing a path towards better understanding of the unconventional phases hosted on the kagome lattice.

Heralded Spectroscopy - A new probe for nanocrystal multiexciton photophysics

Emitters of quantum light are at the core of quantum optic science and a key resource for emerging classical and quantum technologies. Yet, to date, the tools available to study multiple-photon quantum light sources, specifically temporally and spectrally in parallel, have been limited. A prominent example is multiply-excited semiconductor quantum dots - an intriguing system that features rich physics and technological potential but lacks direct observation techniques.

In this talk, I will introduce a new type of spectroscopy,Heralded Spectroscopy, specifically tailored to tackle this challenge. The technique harnesses photon correlations, a resource that has played a seminal role in quantum optics (as exemplified in this year’s Nobel Prize in physics) and is now showing renewed potential with the maturation of novel detector technologies. I will describe the Heralded Spectroscopy method and some of the insights it uncovered into quantum dot physics, as well as current adaptations and their potential to further extend the boundaries of spectroscopy and our understanding of quantum light emitters.

1. GL et al., ACS Photonics, 9 (9), pp. 2891–2904 (2022)
2. GL et al., ACS Nano, 15 (12), pp. 19581-19587 (2021)
3. GL et al., Nano Letters, 21 (16), pp. 6756–6763 (2021)
4. GL et al., Optics Express, 27 (23), pp.32863-32882 (2019)

Quantum Algorithms as the Level-band problem

Many quantum algorithms can be seen as a transition from a well-defined initial quantum state of a complex quantum system, to an unknown target quantum state, corresponding to a certain eigenvalue either of the Hamiltonian or of a transition operator. Often such a target state corresponds to the minimum energy of a band of states. In this context, approximate quantum calculations imply transitions not to a single, minimum energy, state but to a group of states close to the minimum. We consider the dynamics and the results of two possible realizations of such a process - transition of population from a single, initially populated isolated level to quantum states at the edge of a band of levels. The first case deals with time-independent Hamiltonians, while the other with a moving isolated level. We demonstrate that the energy width of the population distribution over the band is mainly dictated by the time-energy uncertainty principle, although the specific shape of the distribution depends on the particular setting. We consider the role of the statistics of the coupling matrix elements between the isolated level and the band levels. We have chosen the multiphoton Raman absorption by an ensemble of Rydberg atoms as the model for our analysis, although the results obtained can equally be applied to other quantum computing platforms.

Journal Club

High-efficiency photoemission from magnetically doped quantum dots driven by multi-step spin-exchange Auger ionization (Nadav Frenkel)

The ability to use visible light for electron photoemission and manipulation of 'hot' charge carriers is of great interest for applications in photochemistry and energy harvesting. In semiconductors, the realization of such schemes is complicated by extremely fast intraband cooling. Auger recombination is a process wherein an exciton recombines non-radiatively, exciting another charge carrier to a higher energy state. In semiconductor nanocrystals, e.g., quantum dots, Auger interactions are enhanced, providing a better chance for manipulating 'hot' carriers before they undergo energy dissipation. Here, we demonstrate that doping CdSe quantum dots with manganese atoms introduces fast spin-exchange interactions, accelerating Auger rates even more. Moreover, we present how the doping 'unlocks' a two consecutive steps Auger process that enables highly efficient electron photoemission under excitation with visible-light pulses.

[1] Livache, C., Kim, W.D., Jin, H.et al.High-efficiency photoemission from magnetically doped quantum dots driven by multi-step spin-exchange Auger ionization.Nat. Photon. 16,433–440 (2022).

Broadband optical phase modulation by colloidal CdSe quantum wells (Daniel Amgar)

Two-dimensional (2D) semiconductors are primed to realize a variety of photonic devices that rely on the transient properties of photogenerated charges, yet little is known on the change of the refractive index. The associated optical phase changes can be beneficial or undesired depending on the application, but require proper quantification. Measuring optical phase modulation of dilute 2D materials is, however, not trivial with common methods.

The work I will present demonstrates phase modulation of light across a broad spectrum by 2D CdSe nanoplatelets using a femtosecond interferometry method. Moreover, they developed a toolbox to calculate the time-dependent refractive index of colloidal 2D materials from widely available transient absorption experiments using a modified effective medium algorithm. The results show that the excitonic features of 2D materials yield a broadband, ultrafast, and sizable phase modulation.

I. Tanghe et al.,Broadband Optical Phase Modulation by Colloidal CdSe Quantum Wells,Nano Lett.,2022, 22, 1, 58–64.

Journal Club

X-Ray Free Electron Lasers from Laser-Plasma Accelerators (Aaron Liberman)

X-Ray free electron lasers (XFELs), able to produce intense, short duration radiation with wavelengths smaller than an angstrom, are a critical tool in physics, chemistry, and biology. They can unlock the ability to image 3D protein structures that have evaded traditional x-ray crystallography. Conventional XFELs, such as the European XFEL, rely on radio-frequency accelerators which are limited in the magnitude of the electric fields they can sustain. Thus, these facilities are kilometer scale, multibillion dollar complexes. Laser-plasma accelerators (LPAs), which can achieve field gradients of over three orders of magnitude greater than RF accelerators, provide a promising path towards the miniaturization of these essential machines. For years, however, the strict requirements on the electron beam quality that XFELs impose prevented the achievement of exponential-gain from LPA generated electron beams. In this talk, I will present the first experimental realization of an exponential-gain, LPA based XFEL. This proof-of-concept experiment promises to path the way to lab-scale XFELs.  

[1] W. Wang et al, “Free-electron lasing at 27 nanometres based on a laser wakefield accelerator,” Nature 595, 516-520 (2021)  

Single-Photon Storage in a Ground-State Vapor Cell Quantum Memory (Ohad Yogev)

Interfaced single-photon sources and quantum memories for photons together form a foundational component of quantum technology. Achieving compatibility between heterogeneous, state-of-the-art devices is a long-standing challenge. We built and successfully interfaced a heralded single-photon source based on cavity-enhanced spontaneous parametric down-conversion in ppKTP and a matched memory based on electromagnetically induced transparency in warm 87Rb vapor. The bandwidth of the photons emitted by the source is 370MHz, placing its speed in the technologically relevant regime while remaining well within the acceptance bandwidth of the memory. Simultaneously, the experimental complexity is kept low, with all components operating at or above room temperature. Read-out noise of the memory is considerably reduced by exploiting polarization selection rules in the hyperfine structure of spin-polarized atoms. For the first time, we demonstrate single-photon storage and retrieval in a ground-state vapor cell memory, with g(2) c; ret = 0:177(23) demonstrating the single-photon character of the retrieved light. Our platform of single-photon source and atomic memory is attractive for future experiments on room-temperature quantum networks operating at high bandwidth.

Buser, Gianni, et al. "Single-Photon Storage in a Ground-State Vapor Cell Quantum Memory." arXiv preprint arXiv:2204.12389 (2022).

Journal Club

Efficient generation of entangled multi-photon graph states from a single atom

Photonic quantum computation has great promise to pave the way for fault-tolerant quantum computers, due to the possibility to scale-up the number of qubits with large entangled states[1]. Yet, photonic quantum computation suits a different computational scheme – Measurement based quantum computation. This scheme demands generation of large entangled/cluster states of photons. The major effort for generating these states is concentrated in probabilistic method using spontenouos parametric down conversion (spdc) and linear optics, e.g. beam splitters and single photon detectors. It can be overcome by utilizing single atom interacting with cavity that can offer a deterministic scheme for generation of large entangled states. In this context, I will elaborate on the results of the following paper[2], which demonstrated generation of up to 14-qubit GHZ states along with up to 12-qubit cluster state.

1. Bombin, H., Kim, I. H., Litinski, D., Nickerson, N., Pant, M., Pastawski, F., ... & Rudolph, T. (2021). Interleaving: Modular architectures for fault-tolerant photonic quantum computing. arXiv preprint arXiv:2103.08612.‏
2. Thomas, P., Ruscio, L., Morin, O., & Rempe, G. (2022). Efficient generation of entangled multi-photon graph states from a single atom. arXiv preprint arXiv:2205.12736. https://arxiv.org/abs/2205.12736

journal club

Probing Infinite Many-Body Quantum Systems with Finite-Size Quantum Siumulators (Lee Peleg)

Experimental studies of synthetic quantum matter are necessarily restricted to approximate ground states prepared on finite-size quantum simulators. In general, this limits their reliability for strongly correlated systems, for instance, in the vicinity of a quantum phase transition (QPT). Here, we propose a protocol that makes optimal use of a given finite-size simulator by directly preparing, on its bulk region, a mixed state representing the reduced density operator of the translation-invariant infinite-sized system of interest. This protocol is based on coherent evolution with a local deformation of the system Hamiltonian. For systems of free fermions in one and two spatial dimensions, we illustrate and explain the underlying physics, which consists of quasiparticle transport towards the system’s boundaries while retaining the bulk “vacuum.” For the example of a nonintegrable extended Su-Schrieffer-Heeger model, we demonstrate that our protocol enables a more accurate study of QPTs. In addition, we demonstrate the protocol for an interacting spinful Fermi-Hubbard model with doping for one-dimensional chains and a small two-leg ladder, where the initial state is a random superposition of energetically low-lying states.

Third harmonic Mie scattering from semiconductor nanohelices (Lotem Alus)

Chiroptical spectroscopies provide structural analyses of molecules and nanoparticles but they require sample volumes that are incompatible with generating large chemical libraries. New optical tools are needed to characterize chirality for the ultrasmall (<1 µl) volumes required in the high-throughput synthetic and analytical stations for chiral compounds. Here we show experimentally a novel photonic effect that enables such capabilities—third-harmonic Mie scattering optical activity—observed from suspensions of CdTe nanostructured helices in volumes <<1 µl. Third-harmonic Mie scattering was recorded on illuminating CdTe helices with 1,065, 1,095 and 1,125 nm laser beams and the intensity was around ten-times higher in the forward direction than sideways. The third-harmonic ellipticity was as high as 3° and we attribute this effect to the interference of chiral and achiral effective nonlinear susceptibility tensor components. Third-harmonic Mie scattering on semiconductor helices opens a path for rapid high-throughput chiroptical characterization of sample volumes as small as 10−5 µl.

Journal club

Attosecond-Level Relativistic Electron Beams from Laser-Plasma Accelerators (Eitan Y. Levine)

Laser-plasma acceleration (LPA) is a mechanism by which a short, ultra-intense laser pulse is focused onto a target, ionizing it and driving a plasma wave in its wake. This wake-field can be used to trap and accelerate electron bunches to relativistic speeds, and also to generate via these electrons a very short x-ray pulse, known as betatron radiation, sharing the duration of its generating electron bunch. Since ultra-short x-ray pulses can be used to probe ultra-short phenomena, measurement and reduction of the accelerated bunch duration are among the goals of the LPA field. In this talk, I will briefly introduce the basic physics of LPA, present the coherent transition radiation (CTR) method for bunch duration and profile measurement, and show predictions for pushing the frontier of ultra-short electron bunch generation.

1. Lundh, O., Lim, J., Rechatin, C. et al. Few femtosecond, few kiloampere electron bunch produced by a laser–plasma accelerator. Nature Phys 7,219–222 (2011). https://doi.org/10.1038/nphys1872
2. Ferri, J. et al.Generation of attosecond electron bunches and x-ray pulses from few-cycle femtosecond laser pulses. Plasma Phys. Control. Fusion 63 045019 (2021).  

Programmable interactions and emergent geometry in an array of atom clouds (Yotam Shapira)

Interacting quantum many-body systems exhibit a wide range of interesting phenomena, such as exotic phases of matter and rich entanglement structures. However these systems are typically analytically intractable and challenging to probe experimentally. This is alleviated by experimentally studying analogous yet controllable systems known as quantum simulators. Here I will follow the realization of Periwal et al [1] and present their realization of a quantum simulator made of an array of atomic ensembles within an optical cavity. The combination of the cavity and a magnetic field gradient along the array axis enables simulation of a wide range of emergent geometries such as a ring, a triangular ladder, a Mobius strip as well as non-Archimedean geometries. The methods and results demonstrated in [1] open up new opportunities for studies of many exciting fields such as quantum gravity, frustrated magnetization, spin glass-models etc.

1. Avikar Periwal, Eric S. Cooper, Philipp Kunkel, Julian F. Wienand, Emily J. Davis & Monika Schleier-Smith, Programmable interactions and emergent geometry in an array of atom clouds, Nature 600, 630-635 (2021).

Journal club

3D printable diffractive optical elements by liquid immersion (Lior Beck)

shape a wavefront, different optical devices can be used, these include diffractive optical elements (DOE), spatial light modulators (SLM) and deformable mirrors. In this work a rather simple and cost-effective method to scale up feature size of DOE has been demonstrated, changing the relevant feature size from tens of nanometers to tens of micrometers. This is done by immersing the DOE in a near index matched solution. The phase accumulated by the DOE can be tuned, this tunability is demonstrated by modifying the point-spread-function (PSF) in a 3D localization microscope, where the position of single molecules in cells were tracked with high precision.

Reut Orange-Kedem, Elias Nehme, Lucien E. Weiss, Boris Ferdman, Onit Alalouf, Nadav Opatovski and Yoav Shechtman  

A look under the tunnelling barrier via attosecond-gated interferometry (Omer Kneller)

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. In my talk I will describe our recent work [1], introducing attosecond-gated interferometry. This scheme probes 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.

[1] Kneller, O., Azoury, D., Federman, Y. et al. A look under the tunnelling barrier via attosecond-gated interferometry. Nat. Photon. 16, 304–310 (2022).

Zoom:https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09

journal club

Measuring exciton diffusion rate, Auger and singlet-singlet annihilation rates, and the true number of chromophores using picosecond time-resolved photon antibunching (Dekel Nakar)

The photon statistics of fluorescence from single quantum systems (single chromophores) shows photon antibunching. In multichromophoric systems, exciton diffusion and subsequent annihilation occurs. These processes also yield photon antibunching but cannot be interpreted reliably. Here the authors develop picosecond time-resolved antibunching to identify and analyze such processes. This method is first used on well-defined multichromophoric DNA-origami structures to precisely determine the distance-dependent rates of annihilation between excitons. Then, this allows to measure exciton diffusion in mesoscopic conjugated-polymer aggregates with different spatial ordering (H- vs. J-type conjugation). The authors distinguish between one-dimensional intra-chain and three-dimensional inter-chain exciton diffusion at different times after excitation and determine the disorder-dependent diffusion lengths. Overall, using this method, excitons can be studied at the single-particle level, enabling the rational design of improved excitonic probes such as ultra-bright fluorescent nanoparticles and materials for optoelectronic devices.

Hedley, G.J., …, Jan Vogelsang et al. Picosecond time-resolved photon antibunching measures nanoscale exciton motion and the true number of chromophores. Nat Commun 12,1327 (2021). https://doi.org/10.1038/s41467-021-21474-z  

Pauli blocking of atom-light scattering (Eran Reches)

Fermi’s golden rule reveals that the transition rate between two coupled states depends on the density of final states. It is well-known, for instance, that a resonant cavity can enhance the spontaneous emission rate of an atom by increasing the density of states of light. Similarly, reducing the density of final momentum modes of the atomic motion is expected to suppress the rate of radiative processes. This can happen for fermionic atoms embedded in a Fermi sea via the Pauli exclusion principle, which forbids final momentum modes already occupied by other atoms.

In my talk I will present the work in Ref. [1], where the authors experimentally demonstrate the suppression of light scattering rates in a quantum degenerate Fermi gas of strontium atoms by up to a factor of 2, compared with a thermal gas. I will also compare key aspects of their experiment to the work of other groups [2,3].

[1] Sanner, C., Sonderhouse, L., Hutson, R. B., Yan, L., Milner, W. R., & Ye, J. (2021). Pauli blocking of atom-light scattering. Science, 374(6570), 979–983. https://doi.org/10.1126/science.abh3483

[2] Deb, A. B., & Kjærgaard, N. (2021). Observation of Pauli blocking in light scattering from quantum degenerate fermions. Science, 374(6570), 972–975. https://doi.org/10.1126/science.abh3470

[3] Margalit, Y., Lu, Y.-K., Top, F. Ç., & Ketterle, W. (2021). Pauli blocking of light scattering in degenerate fermions. Science, 374(6570), 976–979. https://doi.org/10.1126/science.abi6153

Zoom:https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09
 

Journal club

Realization of a 9-qubit Bacon-Shor Code (David Schwerdt)

Recently there have been several experimental demonstrations of quantum error correction (QEC). These demonstrations are of great interest as they pave the way to running large-scale quantum computing protocols that are resilient against physical qubit errors. For any realization of QEC to be viable it must be fault tolerant (FT), in that prevents the spread of errors.

This talk will mainly focus on a FT realization of the Bacon-Shor code in a trapped ion system [1]. The authors demonstrate FT state preparation, stabilizer measurements, and logical-qubit operations. They show the successful correction of any single-qubit errors in a single round of QEC. This work provides an outlook towards implementing circuits with continuously-stabilized logical qubits.

[1] Egan, L. et al. (2021) “Fault-tolerant control of an error-corrected qubit.” Nature 598, 281-286  

3D printable diffractive optical elements by liquid immersion (Lior Moshe Beck)

To shape a wavefront, different optical devices can be used, these include diffractive optical elements (DOE), spatial light modulators (SLM) and deformable mirrors. In this work a rather simple and cost-effective method to scale up feature size of DOE has been demonstrated, changing the relevant feature size from tens of nanometers to tens of micrometers. This is done by immersing the DOE in a near index matched solution. The phase accumulated by the DOE can be tuned, this tunability is demonstrated by modifying the point-spread-function (PSF) in a 3D localization microscope, where the position of single molecules in cells were tracked with high precision.

Reut Orange-Kedem, Elias Nehme, Lucien E. Weiss, Boris Ferdman, Onit Alalouf, Nadav Opatovski and Yoav Shechtman

Zoom:https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09

Why is refractive index so small? From quantum optics to quantum chemistry

It is interesting to observe that all known materials have an index of refraction that is of order unity at visible wavelengths. This is quite different than any other material property (such as density, conductivity, specific heat), which can vary by orders of magnitude, and depends on the system being a gas vs. solid, insulating vs. conducting, etc. Strangely, there is no deep underlying theory of why refractive index has this seemingly universal property. This is despite the immense technological importance that an ultrahigh index material would have, as the index describes how much the wavelength of light can be reduced, and thus directly determines the minimum footprint of optical devices.

Separately, it is well-known within quantum optics that a single, isolated atom can have an extraordinarily strong response to near-resonant light, as characterized by a scattering cross section that is much larger than its physical size. Substituting this known result into standard electrodynamics formulas for material refractive index results in a predicted index of 10^5 at the densities of a solid! Here, we will discuss why these textbook formulas break down, and our ongoing efforts to develop a more fundamental theory of refractive index and its limits. Our theory suggests that the low refractive index observed in everyday life is not necessarily fundamental, and a low-loss, ultrahigh-index material of n~30 might be possible. This theory combines ideas from quantum optics, quantum chemistry, and non-perturbative multiple scattering of light, which suggests why an answer to the refractive index problem might have been elusive in the past.  

Zoom:https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09

Journal club

Pauli blocking of atom-light scattering (Eran Reches)

Fermi’s golden rule reveals that the transition rate between two coupled states depends on the density of final states. It is well-known, for instance, that a resonant cavity can enhance the spontaneous emission rate of an atom by increasing the density of states of light. Similarly, reducing the density of final momentum modes of the atomic motion is expected to suppress the rate of radiative processes. This can happen for fermionic atoms embedded in a Fermi sea via the Pauli exclusion principle, which forbids final momentum modes already occupied by other atoms.

In my talk I will present the work in Ref. [1], where the authors experimentally demonstrate the suppression of light scattering rates in a quantum degenerate Fermi gas of strontium atoms by up to a factor of 2, compared with a thermal gas.

[1] Sanner, C., Sonderhouse, L., Hutson, R. B., Yan, L., Milner, W. R., & Ye, J. (2021). Pauli blocking of atom-light scattering. Science, 374(6570), 979–983. https://doi.org/10.1126/science.abh3483

The image-forming mirror in the eye of the scallop (Arujash Mohanty)

When we talk about eyes, we perceive it as a structure having one or more lenses for focusing incoming light onto a surface (retina). However, light can also be focused using arrays of mirrors (commonly done in telescopes). A biological example of this is the “Pecten scallop”, which can have up to 200 reflecting eyes that focus light onto two retinas. The layered structure of the mirrors is optimized to reflect the wavelengths of light penetrating the eye of the scallop and is tiled with an assembly of square guanine crystals, which reduces optical aberrations. The image is formed by reflection from the mirrors on a double-layered retina used for separately imaging the peripheral and central fields of view. This tiled, off-axis mirror of the scallop eye bears a striking resemblance to the segmented mirrors of reflecting telescopes. I will be talking about the mechanism of such complex imaging system in terms of imaging quality, structural orientation of the mirrors and the control of the size, shape, and packing density of the mirrors (tiles of guanine) that together make up an image-forming mirror at the back of each of the eyes.

The image-forming mirror in the eye of the scallop ( DOI: 10.1126/science.aam9506 )

Zoom:https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09

Boosting electron beam energy in laser-plasma accelerators

From facilitating advanced non-destructive material testing to saving lives with radiation treatments for cancer, particle accelerators are everywhere, playing a definitive role in science and society. Conventional accelerators are limited by the electric field gradients generated in radio-frequency (RF) cavities. Thus, a considerable acceleration length is required to achieve the high energies needed for many applications. Laser-plasma accelerators (LPAs), a newer generation of accelerators that operate on a different paradigm, can overcome this limitation, sustaining accelerating fields three orders of magnitude larger than those in RF cavities. LPAs, therefore, allow for a drastic decrease in accelerator size, reducing price and increasing availability. Yet, several challenges remain before LPAs can replace traditional accelerators. Most significantly, in order to be of use in many real-world applications, LPAs must demonstrate the ability to produce stable, efficient, and high-quality GeV electron beams at a high repetition rate. In my talk, I will present the development of new methods that tackle LPA's limitations and aim to increase efficiency and accelerate more energetic electrons.

ZOOM: https://weizmann.zoom.us/j/99391169077?pwd=cktsZENWT3o1OGlYejRoT2FDQSs0UT09

Journal club

Superresolution Microscopy of Optical Fields (Jonathan Wengrowicz)

A scanning probe microscope has been realized using single trapped 87Rb atoms to measure optical fields with subwavelength spatial resolution. The microscope operates by detecting fluorescence from a single atom driven by near-resonant light and determining the ac Stark shift of an atomic transition from other local optical fields via the change in the fluorescence rate. The microscope benchmarked by measuring two standing-wave Gaussian modes of a Fabry-P´erot resonator with optical wavelengths of 1560 and 781 nm. A spatial resolution of 300 nm attained, which is superresolving compared to the limit set by the 780 nm wavelength of the detected light. Sensitivity to short length scale features is enhanced by adapting the sensor to characterize an optical field via the force it exerts on the atom.

(Emma Deist, Justin A. Gerber, Yue-Hui Lu, Johannes Zeiher and Dan M. Stamper-Kurn)  

Photon control and coherent interactions via lattice dark states in atomic arrays (Roni Ben Maimon)

Ordered atomic arrays with subwavelength spacing have emerged as an efficient and versatile light matter interface, where collective interactions give rise to det of super- and subradiant lattice states. Using a spatial modulation of the atomic detuning, it is possible to address and manipulate the highly subradiant states, also known as lattice dark states. More specifically, the lattice dark states can be utilized to store and retrieve single photon with near-unit efficiency, as well as control the temporal, frequency, and spatial degrees of freedom of the emitted electromagnetic field. These results pave the way towards quantum optics and information processing using atomic arrays.

(Oriol Rubies-Bigorda, Valentin Walther, Taylor L. Patti and Susanne F. Yelin)

ZOOM: https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09

Two-body problem in waveguide quantum electrodynamics

Will consider an interaction of two photons with a periodic array of two-level atoms, coupled to a waveguide. Single-particle eigenstates of this setup are polaritons, hybridized light-atom excitations, that have an intrinsically nonparabolic dispersion law formed by the avoided crossing of light with the atomic resonance. Polaritons repel each other strongly due to the photon blockade. Due to the nonparabolic dispersion, the two-polariton problem becomes significantly different from that of usual massive interacting bosons. In another words, the two-body Dicke model shows new interactions, impossible in e.g. the Tonks-Girardeau gas or a Bose-Hubbard model.  

Specifically, we predict that two-polariton states manifest an interaction-induced localization [1], where the first polariton forms a standing wave in a finite array, that creates a potential well for a second polariton and vice versa. In case when the standing wave has multiple nodes, it drives topologically nontrivial edge states [2]. Contrary to the usual Aubry-André-Harper model, such edge states emerge solely from interactions of two photons with atoms. No external magnetic field, complex lattices or external modulations are required. Mixing between different standing waves results in highly irregular two-polariton states which can be viewed as an interaction-induced quantum chaos [3].  

[1] J.Zhong et al., “Photon-Mediated Localization in Two-Level Qubit Arrays”, Phys. Rev. Lett. 124, 093604 (2020).

[2] A.V. Poshakinskiy et al., “Quantum Hall phases emerging from atom-photon interactions”, npj Quantum Information 7, 34 (2021),

[3] A.V. Poshakinskiy, J.Zhong, A.N. Poddubny, Phys. Rev. Lett. 126, 203602 (2021).

Zoom:https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09  

Laser Defense Systems- Science Fiction Materializing

Laser technology has advanced rapidly from the invention of the laser in the 1960’s to the Mega-Watt lasers of the late 1980’s. Alongside the rapid technology development comes an expectation for laser defense systems which have long been a part of science fiction literature. Nevertheless, the latter have yet to be fielded, coining the popular joke that high power laser systems have been three years away from us, for three decades. Over the last few years, the technology has matured and the operational need for this innovative and game-changing defense system has increased making their entrance to the battlefield imminent.

This Seminar describes how these systems work and focuses on the technological breakthroughs that finally allows their realization- fiber laser power scaling via beam combining, beam focusing and pointing and real-time atmospheric turbulence disturbance correction.

Journal club

Zeptosecond birth time delay in molecular photoionization (Chen Mor)

Ultrafast science is a an ever evolving field, allowing atto-seconds (10^-18 seconds) measurement and control of matter. I will discuss a science paper by Sven Grundmann et al. , where measurements of photoionization in zepto-seconds (10^-21 seconds) scale were performed.Using an electron interferometric technique, Grundmann et al. report a birth time delay on the order of a few hundred zeptoseconds between two electron emissions from the two sides of molecular hydrogen, which is interpreted as the travel time of the photon across the molecule.This work shows great promise for further advancement in ultrafast measurements. SVEN GRUNDMANN et al., science

Full-field quantum optical coherence tomography (Elad Benjamin)

Hong-Ou-Mandel (HOM) interference, the bunching of indistinguishable photons at a beam splitter, is a staple of quantum optics and lies at the heart of many quantum sensing approaches. One such method is quantum optical coherence tomography (QOCT). Classical OCT utilizes low coherence light to preform optical sectioning of a reflective sample, thus allowing for improved resolution in the axial direction and greater depth penetration. Through the HOM effect, QOCT can achieve 2-fold improved axial resolution compared to OCT. Furthermore, it intrinsically negates some dispersion effects, allowing in principle for greater penetration depths. In this talk I will review both OCT and QOCT, and present a recent work from Ibarra-Borja et al. implementing full-field QOCT, thereby bringing us one step closer toward QOCT as a practical bioimaging technique.

[1] C.K. Hong, Z.Y. Ou, and L. Mandel, Phys. Rev. Lett. 59, 2044 (1987)

[2] M.B. Nasr, D.P. Goode, N. Nguyen, G.Rong, L. Yang, B.M. Reinhard, B.E.A. Saleh, and M.C. Teich, Opt. Commun. 282, 1154 (2009).

[3] Z. Ibarra-Borja, C. Sevilla-Gutierrez, R. Ramirez-Alarcon, H. Cruz-Ramirez, and A.B. U'Ren, Photonics Research 8, 51 (2020).

Interplay of machine learning and quantum physics: from ML-enhanced quantum dynamics to quantum machine learning

I will describe our work that explores how quantum physics can benefit from machine learning and how machine learning can benefit from quantum computing. The connection between quantum mechanics and machine learning is through kernels of reproducing kernel Hilbert spaces. I will describe an algorithm to construct kernels that yield Bayesian machine learning models capable of extrapolation in Hamiltonian parameter spaces. I will then show that this algorithm can be adapted for building optimal circuits of a gate-based quantum computer, yielding quantum kernels that outperform conventional classical kernels for small data machine learning tasks. If time permits, I will also show that a support vector machine with a quantum kernel can be designed to be BQP-complete.

Nonlinear Spectroscopy of Nanomaterials

Electric fields are frequently used to manipulate the electronic properties of nanostructured materials. Commonly, such fields split and bend the energy structure of crystalline solids which can, in turn, alter their optical properties, such as their fluorescence due to band-to-band transitions. Furthermore, electric fields can be used, in principle, to modify the crystal potential permanently–by a structural change, or temporarily–as a perturbation.

Here, two separate studies were carried out to characterize the influence of electric fields on quantum-confined semiconductor nanostructures. First, we identified a linear response of the fluorescence of metal halide perovskite nanowires to the presence of an external electric field, which we associate with the forming of an internal dipole. Interestingly, this system often acts as an electret–where the dipole orientation depends on the history of the applied field. The system was modeled using such an assumed built-in potential, providing an analytically derived description ofthenanowires’behavior by adaptation of the carrier dynamics equation.

Additional, nonlinear optics probing of structural changeshadn’tfound significant changes due to the induction of the dipole. In the other part, the possibility of a perturbation of the second-order nonlinear susceptibility in semiconductor nanoplatelets by electrical charging during the fluorescence‘blinking’time was explored. Such perturbation might induce fluctuations of the nonlinear susceptibility tensorx(2) and of dependent processes such as second-harmonic generation (SHG). In order to reveal if such a correlation exists between fluorescence and nonlinear scattering, simultaneous detection of photoluminescence and SHG was conducted on single nanoplatelets placed on fabricated substrates having negligible surface SHG. Our finding shows the absence of a statistically significant correlation between the two mechanisms.

Hybrid seminar - physical seminar at Weismann seminar room A, virtual at - https://weizmann.zoom.us/j/94442528193?pwd=Nm1PZzVzR2w0bGE0OTZ5NzRmRDY5dz09

Imaging with scattered light: using speckles to see deeper and sharper

Scattering of light in complex samples, such as biological tissue, renders most samples opaque to conventional optical imaging techniques, a problem of great practical importance [1].  

However, although random, scattering of coherent light is deterministic, and possess inherent correlations that are maintained even after multiple scattering events. These allow physical correction of scattering [2], and computational reconstruction of diffraction-limited images through visually opaque samples and around corners [3], combining light and sound [4,5]. I will present the fundamental principles and limitations of the novel approaches that aim at undoing random scattering. If time permits, I will present how the same principles can also be employed to realize miniature lensless endoscopes [6].  

References

[1] Z. Merali, Optics: Super vision, Nature 518, 158 (2015).

[2] T. Yeminy, O. Katz, Guidestar-free image-guided wavefront shaping, Science Advances, 7, 21 (2021).

[3] O. Katz et al. Non-invasive single-shot imaging through scattering layers and around corners via speckle correlations. Nature photonics, 8(10), 784-790 (2014).

[4] E. Hojman et al. Photoacoustic imaging beyond the acoustic diffraction-limit with dynamic speckle illumination and sparse joint support recovery, Optics Express 25 (5), 4875-4886 (2016).

[5] M. Rosenfeld, D. Doktofsky, G. Weinberg, Y. Li, L. Tian, O. Katz, Acousto-optic Ptychography, Optica, (2021).

[6] W. Choi et al. Fourier holographic endoscopy for label-free imaging through a narrow and curved passage, arXiv:2010.11776 (2020).

journal club

Understanding the Berry phase – a bridge between pendulums to solid state physics (Lior Faeyrman)

The Berry phase, generalized by Sir Michael Berry [1], is canonically taught as a phase that appears due to an adiabatic evolution in a quantum system, avoiding the profound connection to geometry and classical mechanics. In this talk, I would like to try to give an intuition to the Berry phase in solid state physics through the help of a classical analog – the Foucault pendulum [2]. By understanding how the Berry phase is manifest in a simple classical example, one can then gain useful intuition and insights for the more abstract solid state case.

[1] Berry, M. V., 1984, Proc. R. Soc. London, Ser. A 392, 45.

[2] Jens von Bergmann, HsingChi von Bergmann ,” Foucault pendulum through basic geometry”, American Journal of Physics 75, 888 (2007); https://doi.org/10.1119/1.2757623  

Purcell-enhanced dipolar interactions in nanostructures (Inbar Shani)

Skljarow, A., Kübler, H., Adams, C. S., Pfau, T., Löw, R., & Alaeian, H. (2021). Purcell-enhanced dipolar interactions in nanostructures. arXiv preprint arXiv:2112.11175.
Strong light-induced interactions between atoms are known to cause nonlinearities at a few-photon level, which are crucial for applications in quantum information processing. Compared to free space, the scattering and the light-induced dipolar interaction of atoms can be enhanced by a dielectric environment. For this Purcell effect, either a cavity or a waveguide can be used. By combining the high densities achievable in thermal atomic vapors with an efficient coupling to a slot waveguide, one can exhibit repulsive interactions that are further enhanced by a factor of 8. This enhancement may pave the way towards a robust scalable platform for quantum nonlinear optics and all-optical quantum information processing at room temperature.

Atoms in lattices, cavities and tweezers

I will present two recent results from my laboratory where we use ultracold atoms to explore various aspects of quantum science.  In the first, we study the evolution and transport of atoms in two-dimensional honeycomb lattices.  We reveal how parallel transport through band touching points leads to non-Abelian non-holonomy that characterizes the geometric singularity at the band touching point, and also move toward studying flat-band physics in excited bands of the lattice.  In the second, we demonstrate the use of high-finesse optical cavities to perform rapid, high-fidelity measurements of the state of a single-atom optical tweezer trap, with important applications to the use of tweezer arrays for quantum simulation and computation.  I will wrap up by presenting some ideas about the potential role of electromagnetic vacuum fluctuations as a catalyst for photochemistry, and about producing ultracold gases from a new family of elements.

Seeing life in a new light

The progress of biomedical sciences depends on the availability of advanced instrumentation and imaging tools capable of attaining the state of biological systems in vivo without using exogenous markers. Mechanical forces and local elasticity play a central role in understanding physical interactions in all living systems. We demonstrate a novel way to image microscopic viscoelastic properties of biological systems using Brillouin microspectroscopy [1]. In my talk, I will discuss the ways how an old spectroscopic tool can be used for real time microscopic imaging [2-3] and provide possible solutions to long standing problems in Life Sciences and Medicine [4-6].

References

[1] Zh. Meng, A. Traverso, C. Ballmann, M. Troyanova-Wood, and V. V. Yakovlev, “Seeing cells in a new light: a renaissance of Brillouin spectroscopy,” Advances in Optics and Photonics 8(2), 300-327 (2016).

[2] Zh. Meng, S. C. Bustamante-Lopez, K. E. Meissner and V. V. Yakovlev, “Subcellular imaging of mechanical and chemical properties using Brillouin microspectroscopy,” Journal of Biophotonics 9(3), 201-207 (2016).

[3] C. W. Ballmann, Zh. Meng, A. J. Traverso, M. O. Scully, and V. V. Yakovlev “Impulsive Brillouin microscopy,” Optica 4(1), 124-128 (2017).

[4] Zh. Meng, T. Thakur, C. Chitrakar, M. K. Jaiswal, A. K. Gaharwar, and V. V. Yakovlev, “Assessment of local heterogeneity in mechanical properties of a bulk hydrogel network,” ACS Nano 11(8), 7690–7696 (2017).

[5] M. Troyanova-Wood, Zh. Meng, and V. V. Yakovlev, “Differentiating melanoma and healthy tissues based on elasticity-specific Brillouin microspectroscopy,” Biomedical Optics Express 10(4), 1774-1781 (2019).

[6] D. Akilbekova, V. Ogay, T. Yakupov, M. Sarsenova, B. Umbayev, A. Nurakhmetov, K. Tazhin, V. V. Yakovlev, Zh. Utegulov, “Brillouin spectroscopy and radiography for assessment of viscoelastic and regenerative properties of mammalian bones,” Journal of Biomedical Optics 23(9), 097004 (2018).

Optomechanics and momentum transfers in inhomogeneous ultra-cold gases

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 will discuss the problem of momentum transfers that follow the refraction and the reflection of light by inhomogeneous ensembles of ultra-cold atoms.
As a correction to a paper recently published, 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. We then study the reflection of light by a dilute cloud and measure the force that acts on the atoms as a result. We show how resulting momentum transfers can be used to probe the dynamic of matter-wave gratings in Bose-Einstein condensates.  

Special seminar – note the time

Hybrid seminar – In Weismann auditorium and zoom - https://weizmann.zoom.us/j/99871493260?pwd=K01BTGkwVWFRUzFQQjBTb2VIZ01xdz09

Journal club

Diffractive Focusing and guiding of waves using slits (Amit Pando)

The diffraction of waves by slits has been studied for centuries, from light waves to more recently, matter waves. While intuition might suggest that a wave passing through a slit will expand, it has recently been demonstrated that the wave actually focuses before expanding. I will present this mechanism, as well as a work in which the effects of such diffractive focusing have been further manipulated in order to create diffractive waveguides[1]: Periodic arrays of slits can be used to guide waves over a long distance with comparable energy losses to refractive waveguides. This has been demonstrated for both plasmonic waves and surface gravity water waves, but could be used for any wave which can be effectively blocked by such slits.

[1] Weisman, D., Carmesin, C. M., Rozenman, G. G., Efremov, M. A., Shemer, L., Schleich, W. P., & Arie, A. (2021). Diffractive guiding of waves by a periodic array of slits. Physical Review Letters, 127(1), 014303.

Spin Quantum Heat Engine Quantified by Quantum Steering (Jonathan Wengrowicz)

Following the rising interest in quantum information science, the extension of a heat engine to the quantum regime by exploring microscopic quantum systems has seen a boom of interest in the last decade. Although quantum coherence in the quantum system of the working medium has been investigated to play a nontrivial role, a complete understanding of the intrinsic quantum advantage of quantum heat engines remains elusive. We experimentally demonstrate that the quantum correlation between the working medium and the thermal bath is critical for the quantum advantage of a quantum Szilárd engine, where quantum coherence in the working medium is naturally excluded. By quantifying the nonclassical correlation through quantum steering, we reveal that the heat engine is quantum when the demon can truly steer the working medium. The average work obtained by taking different ways of work extraction on the working medium can be used to verify the real quantum Szilárd engine.

Journal club

Anyonic-parity-time symmetry in complex-coupled lasers (Sagie Gadasi)

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. 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.

In this work we study this novel symmetry and demonstrate it experimentally 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, tuning the coupling in the same physical system, allows us to realize the more familiar 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.

Reference: [1] G. Arwas, S. Gadasi, I. Gershenzon, A. Friesem, N. Davidson, and O. Raz, Anyonic Parity-Time Symmetric Laser, ArXiv:2103.15359v1 [Physics] (2021).

Realizing a topological insulator with coupled vertical-cavity lasers (Eran Bernstein)

Topological insulator lasers are arrays of semiconductor lasers that exploit fundamental features of topology to force all emitters to act as a single coherent laser. I will present a work realizing such a topological insulator laser in an array of vertical-cavity surface-emitting lasers (VCSELs)[1]. I will focus on the topological properties of the scheme that is demonstrated for coupling lasers, and how it generates protected edge states and robust phase locking. This is an example for the generality of topological insulators to non-electronic wave systems such as photonics, cold atoms, and acoustics.

[1] Alex Dikopoltsev, Tristan H. Harder, Eran Lustig, Oleg A. Egorov, Johannes Beierlein, Adriana Wolf, Yaakov Lumer, Monika Emmerling, Christian Schneider, Sven Höfling, Mordechai Segev, Sebastian Klembt. Topological insulator vertical-cavity laser array. Science, 2021; 373 (6562): 1514 DOI: https://doi.org/10.1126/science.abj2232

Journal club

Photon storage in ordered atomic arrays (Yakov Solomons)

Quantum memory is an essential ingredient in the field of quantum information processing. One of the promising approaches for quantum memory is photon storage, in which an optical state is reversibly converted to an atomic excitation.In this talk, I will present our recent work on photon storage in ordered atomic arrays. These arrays, which are characterized by collective coupling to light [1], suppress the light emission into undesirable directions. This property makes the ordered arrays an excellent platform for efficient light storage [2].

[1] E. Shahmoon, D. S. Wild, M. D. Lukin, and S. F. Yelin, Cooperative resonances in light scattering from two-dimensional atomic arrays, Physical Review Letters 118, 113601 (2017).

[2] M. Manzoni, M. Moreno-Cardoner, A. Asenjo-Garcia, J. V. Porto, A. V. Gorshkov, and D. Chang, Optimization of photon storage fidelity in ordered atomic arrays, New Journal of Physics 20, 083048 (2018).

Description and first application of a new technique to measure the gravitational mass of antihydrogen (Raz Boaz)

Physicists have long wondered whether the  gravitational interactions between matter and antimatter might be different from those between matter and itself. Although there are many indirect indications that no such differences exist and that the weak equivalence principle holds, there have been no direct, free-fall style, experimental tests of gravity on antimatter. Here we describe a novel direct test methodology; we search for a propensity for antihydrogen atoms to fall downward when released from the ALPHA antihydrogen trap. In the absence of systematic errors, we can reject ratios of the gravitational to inertial mass of antihydrogen >75 at a statistical significance level of 5%; worst-case systematic errors increase the minimum rejection ratio to 110. A similar search places somewhat tighter bounds on a negative gravitational mass, that is, on antigravity. This methodology, coupled with ongoing experimental improvements, should allow us to bound the ratio within the more interesting near equivalence regime.

https://www.nature.com/articles/ncomms2787

Free-electron interaction with engineered plasmonic fields

The interaction of free electrons with light has been a continuous source of new discoveries and technologies, ranging from medical imaging [1] and microscopy [2] techniques to bright, ultrafast x-ray sources [3] and particle accelerators [4]. In recent years, particular attention was devoted to such interactions occurring in platforms with a strong near-field component [5,6], revealing novel ways to manipulate the wavefunction of free electrons in an inherently quantum-mechanical way. As such, it is clear that precise control over the near-field distribution can enable new physical observations and technological capabilities, making it the main focus of our work.

By passively and actively controlling the transverse distribution of a plasmonic field, we generated various high-quality electron probability distributions and shifted between them, while altering the resulting pattern through post-selection [7]. By employing a hybrid photonic-plasmonic waveguide design to control the longitudinal near-field distribution, 2D Cherenkov radiation and its quantized nature were observed for the first time, along with a record-high free-electron - photon coupling strength [8]. Our investigation pushes the limit of free-electron interactions with light to new regimes, establishing free electrons as an alternative route for quantum optics and making a significant step towards the long-standing goal of arbitrary spatial modulation of electrons.

[1] A. Ruggiero et al, J. Nucl. med. 51, 1123-1130 (2010)

[2] B. Barwick et al, Nature 462, 902–906 (2009)

[3] J. Duris et al, Nat. Photon. 14, 30–36 (2020)

[4] E. A. Peralta et al, Nature 503, 91–94 (2013)

[5] A. Feist et al, Nature 521, 200–203 (2015)

[6] G. M. Vanacore et al, Nat. Mater. 18, 573–579 (2019)

[7] S. Tsesses et al, CLEO: QELS_Fundamental Science, FM1L. 2 (2021); Manuscript under review

[8] Y. Adiv et al, CLEO: QELS_Fundamental Science, FM1L. 6 (2021); Manuscript under review