Seminars

AMOS Journal Club

LWFA with a Flying-Focus Wakefield  (Liberman) 

Laser-wakefield accelerators (LWFAs) have demonstrated the ability to generate high-quality, monoenergetic electron beams. Yet, efforts to achieve higher electron energies are by electron dephasing and beam diffraction. One promising approach to mitigating these limitations is the use of structured light to control the on-axis propagation velocity within LWFAs. This method promises an improved balance of extended acceleration distances and strong accelerating gradients.

In this talk, we report the first experimental observation of wakefields driven by such structured-light beams as well as the first experimental evidence of the mitigation of dephasing in electron acceleration. Spatiotemporally engineered laser pulses are focused using a specialized mirror to produce a quasi-Bessel beam, and the resulting wakefields are directly measured using femtosecond relativistic electron microscopy. We experimentally demonstrate control over the on-axis propagation velocity of the wakefield and follow its evolution throughout the focal region. We investigate how targeted spatiotemporal modifications affect both the wakefield structure and its propagation velocity. Finally, we present the first successful acceleration of electrons using these wakefields, demonstrating partial mitigation of dephasing.

[1] C. Caizergues et al. “Phase-locked laser-wakefield electron acceleration,” Nat. Photonics. 14, 8 (2020)

[2] J.P. Palastro et al. “Dephasingless laser wakefield acceleration,” Phys. Rev. Lett. 124, 134802 (2020)

[3] A. Liberman et al.,“Direct Observation of a Wakefield Generated with Structured Light,” Nat. Commun. 16, 10957 (2025)

[4] A. Liberman et al.,“First Electron Acceleration in a Tunable-Velocity Laser Wakefield,” under review. (https://arxiv.org/abs/2509.21098)

[5] A. Liberman et al.,“Probing Flying-Focus Wakefields,” under review. (https://arxiv.org/abs/2510.16950)

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

Photonic quantum gates and two-photon processes in Waveguide QED (Levy)

The search for passive, deterministic conditional gates between photons remains a major objective within the quantum optics and Waveguide QED community. Many proposals have emerged using different quantum non-linear media such as Rydberg atoms, Kerr non-linearities or V-type emitters. We wanted to answer the question: can the simplest form of quantum non-linearity—a two-level emitter—be harnessed to construct a photonic conditional gate? The use of two-level emitters has posed challenges, as strong photon correlations usually come at the price of significant distortions in the wavepacket spectrum. I will present our approach to overcome these limitations through a novel architecture [1]. This design can be realized within a two-mode chiral Waveguide QED framework,

such as the one resulting from two-level emitters coupled to a topological waveguide. I will also discuss a recent proposal designed for Circuit QED using transmon dimers non-locally coupled to a waveguide [2].

[1] T. Levy-Yeyati, C. Vega, T. Ramos and A. Gonzalez-Tudela, PRX Quantum 6, 010342 (2025)

[2] T. Levy-Yeyati, T. Ramos and A. González-Tudela, arXiv:2507.05377 (2025).

 

Error-correctable microwave dual-rail qubits

Dual-rail qubits represent a promising platform for fault-tolerant quantum technologies since their erasure errors allow a reduced error threshold when embedded in an outer code. In superconducting systems, these qubits can be implemented in two-transmon or two-cavity systems with a single excitation. Better error protection requires reducing the erasure rate, which is possible with multiple excitations in microwave cavities where photon loss primarily leads to correctable errors. I will present the four-photon variant of this encoding, discussing the tools needed for full quantum control including initialization, logical gates, error correction, and measurements. I will then show that universal single-qubit control requires only a simple sequence of two types of quantum gates and discuss tolerance of the control tools to errors caused by photon loss and in the auxiliary circuitry. With the ability to correct the dominant error, the multi-photon dual-rail encodings have the potential to greatly reduce the size of the outer code needed for fault-tolerant quantum operation.

 

Unlocking New Capabilities for Quantum Computation and Simulation with Neutral Atom Arrays

Neutral atom arrays have become a frontrunner in the race for utility scale quantum computation [1], building on their reconfigurability [2], scalability [3] and high fidelity for all operations [4] - idling, detection, single- and two-qubit gates. They have also produced large scale quantum simulation of complex many-body systems [5]. However, they still suffer key bottlenecks that constrain their operational speed, their deep quantum circuit implementation and the range of physical models thye are able to simulate. In this talk, I will show how my recent work can bend these constraints and sometimes completely break them. I will present my work on accelerated detection of the atoms via high-lying energy states (Rydberg states) [6] and introduce novel protocols for reconfigurable multi-qubit gates [7], promoting improved circuit implementation speed and error rates. I will show how arbitrary spin-spin interaction models can be implemented in atom arrays through Floquet engineering [8], extending their ability to simulate many important quantum magnetism models. I will then update on our current progress in building a continuously operating neutral atom quantum processor, which mitigates the negative influences of atom loss, and present a new scheme we developed to operate atom array systems for this purpose [9]. Lastly, I will touch on the final frontier - how to increase system size to a utility scale number of qubits - and provide my own solution to it: free electron quantum interconnects between neutral atom quantum processing modules.  

References

[1] D. Bluvstein et al, Nature 649, 39–46 (2026)

[2] D. Bluvstein et al, Nature 604, 451–456 (2022)

[3] H. J. Manetsch et al, Nature 647, 60–67 (2025)

[4] D. Bluvstein et al, Nature 626, 58–65 (2024)

[5] A. Browaeys & T. Lahaye, Nat. Phys. 16, 132–142 (2020)

[6] T. Sumarac*, E. Qiu*, S. Tsesses* et al, arXiv

[7] J. Bender*, S. Tsesses* et al, in preparation

[8] N. Nishad et al, Phys. Rev. A 108, 053318 (2023)

[9] E. Qiu*, T. Sumarac*, P. Niu* et al, arXiv:2509.12124

Do homonuclear diatomic molecules have a permanent dipole moment?

Our atmosphere consists mainly of homonuclear diatomic molecules (N₂ and O₂). However, the molecules that affected the Earth's temperature are only present in a much smaller concentration. The reason is that molecules like CO₂ have a permanent dipole moment, which allows them to absorb and emit infrared radiation efficiently. In contrast, homonuclear diatomic molecules are transparent to this radiation due to their symmetry and lack of a permanent dipole moment (within the Born-Oppenheimer approximation). 

In this talk, a new study will be presented on the internal dynamics of hot diatomic molecules of Ag₂^- and Cu₂^-. The molecules were produced in a hot ion source, stored in an electrostatic ion beam trap, and a CW laser was used to photo-detach the molecules while in the trap. A special electron spectrometer, built inside the trap, was used to monitor the photoelectron spectra for up to several seconds after molecular production. Internal molecular dynamics were observed, suggesting spontaneous cooling due to dipole transitions.

The above finding supports a new speculation about primordial star formation. This speculation will also be discussed.

Ultracold Atom-Ion interactions

In this seminar, I will describe a decade of research in our lab, in which we studied collisions between ions and atoms in the ultracold regime. I will review two different research directions and findings. The first was the study of the effect of the strong, time-dependent, ion trap on collision dynamics. I will show that binary collisions in the presence of the trap result in highly non-equilibrium dynamics, chaotic behavior, and the formation of quasi-bound molecular states. The second research direction was the search for quantum signatures in ultracold atom-ion collisions. Despite the fact that the trap induced, non-equilibrium, dynamics limits atom-ion collisions to energies which are orders of magnitude above the quantum threshold, quantum signatures are still observed. This quantum behavior, far from the quantum regime, results from the long-range character of atom-ion interactions. 

Cancelled : Light-matter interaction from the photon perspective

Cancelled: In this discussion, we will take least conventional route to look at light-matter interaction from perspective of light, rather than conventional view as it is dictated solely by the material. Obviously, every optical process is a light–matter interaction, hence the transition probability is equally a property of the electromagnetic field itself. We will show that by shaping, confining, or conditioning the optical field, even in simple experimental configurations, one can fundamentally alter light–matter interactions and induce dramatic changes in optical behavior. First, using silicon as a model system, we illustrate how engineered multi-photon processes enable broadband detection across a multi-octave spectral range, including label-free, chemically specific IR tomography and high-speed hyperspectral IR video imaging. Second, we introduce a new photonic phenomenon that stems directly from the Heisenberg uncertainty principle governing the spatial and momentum degrees of freedom. When light is confined to sub-2 nm dimensions, its momentum becomes comparable to that of electrons in solids. Under these conditions, photons acquire de Broglie wavelengths capable of matching electronic states, greatly enhancing optical transition rates - a regime previously associated only with X-ray photons in classical Compton scattering. This overlooked photonic mechanism opens a new pathway for manipulating optical transitions, with profound implications for semiconductor physics and photonic technologies.

Nonlinear optics in high-finesse Fabry-Perot microcavities with LiNbO3

The increase in demand for computation and the associated energy spending have been motivating the exploration of photonic analog computing schemes, to exploitie their superior bandwidth and improved energetic efficiency. To that end, nonlinear fibers and integrated waveguides based on thin-film LiNbO₃ have become the dominant platforms of research, supporting, for example, optical parametric amplifiers and oscillatiors¹, optical switches², and coherent Ising machines³. However, realizing similar functionalities in a surface emitting geometry has the potential to complementarily promote massively parallel and spatially encoded computing and simulations, as well as quantum information and image-processing⁴. 

In this talk, I will present recent results from our work towards this objective, using high-finesse distributed Bragg-reflector (DBR)- based surface-emitting microcavities, embedded with LiNbO₃ as a second-order nonlinear material. Specifically, I will discuss our (yet) simulative research towards developing optical parametric oscillators in that geometry⁴, drafting the main design considerations and expected performance. Another project I will describe uses sum- and difference-frequency generation within the cavity to instantaneously switch optical signals into or out of the cavity⁵. This intracavity optical gating then allows following the spatio-temporal dynamics of the resonant optical fields and their light-matter interactions. It will be useful for following the evolution of simulation and computation processes, and for schemes for deterministic quantum information storage and extraction⁵

References:

1.               McKenna, T. P. et al. Ultra-low-power second-order nonlinear optics on a chip. Nat. Commun. 13, 4532 (2022).

2.               Guo, Q. et al. Femtojoule femtosecond all-optical switching in lithium niobate nanophotonics. Nat. Photonics 16, 625–631 (2022).

3.               Yamamoto, Y. et al. Coherent Ising machines—optical neural networks operating at the quantum limit. Npj Quantum Inf. 3, 1–15 (2017).

4.               Yanagimoto, R. et al. Design and function of a vertical micro-cavity optical parametric oscillator. J. Phys. Photonics 7, 045031 (2025).

5.               Karni, O., Vaswani, C. & Chervy, T. Ultrafast optical gating in a nonlinear lithium niobate microcavity. Preprint at https://doi.org/10.48550/arXiv.2510.11965 (2025).

Special AMOS seminar: The Journey from eV to MW: Diode Pumped Alkali Laser

In this talk I will go through the motivation for the development of Diode Pumped Alkali Laser (DPAL) in Rafael and worldwide. I'll cover the working mechanisms, the advantages and challenges of DPAL. Through this talk I'll show the importance of diving deep into the physics of this technology and how each physical phenomena can influence on its development. 

Journal club

No oscillating subradiant correlations in a strongly driven quantum emitter array

Jiaming Shi

We theoretically study time-dependent correlations in a strongly driven array of N two-level atoms, coupled to photons in a waveguide. We focus on the spectrum of the Liouvillian superoperator, which determines the correlation decay rates and the frequencies. Our main finding is the suppression of subradiant correlations between atomic states by a strong coherent driven. In this talk, I will present the basic concepts starting from a simple toy model, and conclude by demonstrating the suppression numerically, together with a rigorous analytical proof based on the spectral decomposition of the Liouvillian using the spectral theory of simplicial complexes and posets.[1]

[1] J. Shi, N. Leppenen, R. Tessler, and A. N. Poddubny, arXiv:2509.09993 (2025)

Quantum nonlinear optics with counter-propagating photons

Ashley Harkavi

We realize strong dissipative interactions between counter-propagating photons mediated by Rydberg polaritons. In this new geometry, where photons propagate in opposite directions, we reach a record-long anti-correlation range exceeding 1μs. This counter-propagating configuration is fundamentally different from the co-propagating one, allowing us to use pulses that are long enough to transmit through the polariton bandwidth yet short enough to fit within the interaction range. We observe full-pulse suppression, controllable via the relative pulse timing, constituting a major step towards deterministic quantum gates. [1]

[1] B. C. Das, A. Harkavi, A. Prakash, A. Nakav, L. Drori, and O. Firstenberg, arXiv:2506.01124 (2025)

Joint AMOS and Quantum Special Seminar

Macroscopic Quantum Phenomena in Electric Circuits – Then and Now  - The 2025 Nobel in Physics 

In 1985, John Clarke, Michel Devoret, and John Martinis demonstrated that macroscopic degrees of freedom – currents and voltages in electric circuits – show clear signatures of quantum behavior, such as quantized energy levels and quantum tunneling. 
In this seminar, I will revisit those pioneering experiments, which were recognized by the 2025 Nobel Prize in Physics, and explain how they set the stage for today’s superconducting quantum processors. I will then present results from our group using these circuits to explore how measurement shapes quantum dynamics.

Generalized effective dynamics via an operator cumulant expansion

Understanding time-dependent systems is a central challenge in both classical and quantum physics. From driven quantum circuits to oscillating classical systems, many of the most interesting systems in physics are inherently time-dependent. Yet, capturing their behavior in a tractable form is often difficult. The key difficulty lies in deriving _effective generators_ that accurately capture the dynamics on the time-scales of interest, while systematically eliminating fast degrees of freedom or rapid modulations without losing any important contributions they add to the dynamics of interest.

In this talk, I will present a general and systematic framework for deriving slow effective dynamics from arbitrary time-dependent generators, using basic ideas from free algebra and rough paths theory. Unlike traditional approaches that rely on periodic or adiabatic driving, our method applies to systems with _arbitrary_ time dependencies and accommodates dynamics generated by any linear operator—Hamiltonian or not, quantum or classical, open or closed. This versatility enables consistent modeling of systems that exhibit strong modulation, dissipation, or non-adiabatic effects.

Our approach provides a unified lens for understanding seemingly disparate methods, such as  Hamiltonian-based techniques such as Lie-transform Perturbation Theory (LPT) and averaging-based methods like Time-Coarse Graining (TCG), revealing their structural equivalence through the lens of generalized cumulants. It further clarifies how non-Hamiltonian terms can naturally emerge from averaging procedures, even in closed or purely classical systems. We illustrate the versatility of the method through two complementary examples. In the classical domain, we analyze a damped, parametrically driven Kapitza pendulum, extending its study to dissipative regimes and time dependencies that had not been previously explored. In the quantum setting, we investigate a non-adiabatic parametron, uncovering effects that arise specifically from the breakdown of adiabaticity. Together, these examples demonstrate how the cumulant framework captures rich dynamical behavior across both classical and quantum systems, Hamiltonian and non-Hamiltonian alike.

References
1.    Bello et al., “Systematic Time-Coarse Graining,” Phys. Rev. Appl. 23, 054042 (2025).
2.    Bello et al., “Generalized Time-Coarse Graining via an Operator Cumulant Expansion,” arXiv:2510.00380 (2025).
 

Special AMOS seminar: Machine Learning at the Physical Limits: Energy, Accuracy and Quantum Security

The AI revolution has renewed interest in the fundamental limitations of computation set by physics. Thermodynamics imposes limitations on the energy cost of irreversible operations, while quantum mechanics imposes limitations on information access. A wave of in-physics AI mitigates these constraints by relaxing fixed-precision requirements and exploiting reversibility where the logic permits. 

In this talk, I will present our advances in in‑physics machine learning, both in the radio‑frequency domain [1–2] and in the optical domain [3–5], that surpass the thermodynamic limitations of digital AI accelerators. I will then turn to optical computing for secure multiparty deep learning [6], where privacy is guaranteed by quantum mechanics.

1. Vadlamani*, Sulimany*,…, Englund. “Machine Intelligence on Wireless Edge Networks”. arXiv:2506.12210 (2025).
2. Gao, Vadlamani, Sulimany,…, Chen. “Disaggregated Deep Learning via In-Physics Computing at Radio Frequency”. arXiv:2504.17752 (2025).
3. Sulimany, Siago, Bandyopadhyay, Hamerly, Englund. “Photodetection Free Optical Machine Learning via Rectification”. CLEO (2025) (to appear).
4. Bandyopadhyay, Sulimany,…, and Englund “A Three-Terminal Nanophotonic Integrator for Deep Neural Networks” OFC, pp. 1-3. (2025).
5. Bacvanski, Vadlamani, Sulimany, and Englund. “QAMNet: Fast and Efficient Optical QAM Neural Networks” arXiv:2409.12305 (2024).
6. Sulimany, Vadlamani, Hamerly, Iyengar, Englund “Quantum-Secure Multiparty Deep Learning”. arXiv:2408.05629 (2024).

PhD Defense: Superconducting Circuits: from Robust Qubits to Quantum Jumps and the Quantum Zeno Effect

Superconducting qubits are a leading platform for quantum computing, but their performance is limited by short memory lifetimes. In this work, we present a new superconducting cavity that extends coherence times to 34 milliseconds—about ten times longer than previous records. This advance allows the storage of complex quantum states and points toward more reliable, error-corrected quantum processors.

We also investigate the fundamental physics of quantum jumps in a superconducting system. By varying measurement strength, we observe clear transitions between smooth quantum oscillations and discrete jump-like behavior. These results clarify how measurement shapes quantum dynamics and deepen our understanding of the boundary between coherence and collapse.

Zoom Link: https://weizmann.zoom.us/j/97255526827?pwd=G1bRe2OHc5j6GSBFiAypURK7Vi8M50.1 

Ultra-High Resolution CZT detectors: Expanding Horizons of Gamma-Ray Imaging and Applications

Recent advances in nuclear medical imaging are driving progress in solid-state detectors, with pixelated CdZnTe (CZT) emerging as a leading technology thanks to their excellent energy resolution and room-temperature operation. The first demonstration of quantum entanglement in the MeV regime may open new opportunities for applications such as Positron Emission Tomography (PET), where pairs of 511 keV gamma photons are detected following positron–electron annihilation in the tissue. Conventional PET suffers from scattering and random coincidences, typically mitigated through nanosecond timing in scintillator detectors, a performance that solid-state systems cannot match. This experimental result, however, suggests that CZT-based PET could achieve comparable performance without such stringent timing requirements.

Although CZT detectors have achieved significant improvements in energy resolution and uniformity, their spatial resolution remains constrained by pixel size. A novel approach now combines CZT detectors with machine learning trained on high-fidelity simulated data, enabling unprecedented improvement in both spatial and energy resolution. This creates a unique synergy: gamma-camera–level energy resolution with spatial precision comparable to mid-range x-ray detectors.

These innovations pave the way for intelligent, ultra-high-resolution and cost-effective detectors, offering revolutionary capabilities for medical, industrial, and scientific imaging.

Special AMOS seminar: Massively multiplexed wide-field photon correlation sensing

Temporal photon correlations have been a crucial resource for quantum and quantum-enabled optical science for over half a century. However, attaining non-classical information through these correlations has typically been limited to a single point (or, at best, a few points) at a time. Here, we perform a massively multiplexed wide-field photon correlation measurement using a large 500×500 single-photon avalanche diode array, the SwissSPAD3. We demonstrate the performance of this apparatus by acquiring wide-field photon correlation measurements of single-photon emitters and illustrate two applications of the attained quantum information: wide-field emitter counting and quantum-enabled super-resolution imaging (by a factor of √2). The considerations and limitations of applying this technique in a practical context are discussed. Ultimately, the realization of massively multiplexed wide-field photon correlation measurements can accelerate quantum sensing protocols and quantum-enabled imaging techniques by orders of magnitude.

Paper - https://doi.org/10.1364/OPTICA.550498

Journal club

Arpit Behera

Erasure cooling, control, and hyperentanglement of motion in optical tweezers

Coherently controlling the motion of single atoms in optical tweezers would enable new applications in quantum information science. To demonstrate this, we first prepared atoms in their motional ground state using a species-agnostic cooling mechanism that converts motional excitations into erasures, errors with a known location. This cooling mechanism fundamentally outperforms idealized traditional sideband cooling, which we experimentally demonstrated. By coherently manipulating the resultant pure motional state, we performed mid-circuit readout and mid-circuit erasure detection through local shelving into motional superposition states. We lastly entangled the motion of two atoms in separate tweezers and generated hyperentanglement by preparing a simultaneous Bell state of motional and optical qubits, unlocking a large class of quantum operations with neutral atoms.

[1] https://www.science.org/doi/10.1126/science.adn2618

Felix Ribuot-Hirsch

Testing the combination of Quantum Mechanics with General Relativity: NASA's Deep Space Quantum Link

Can we design experimental tests of Quantum Field Theory in Curved Space-Time (QFT-CST) and measure data in real gravitational gradient to valid one of Physics's jewel theory? Since Stephen Hawking's groundbreaking QFT-CST calculations and prediction of Black Hole evaporation, theorists had to satisfy themselves with faint cosmological predictions or studies of laboratory analogs. With the advent of the second quantum revolution, a new frontier opens: quantum technologies now reach space and allow for testing physics foundation. This presentation will review the efforts lead by the NASA in their project "The Deep Space Quantum Link", which aims at performing a measurement of the gravitational redshift via quantum-optical interferometry in space with quantum light sources and detectors. Competitive QFT-CST test proposals, global quantum space missions and consequences on quantum optics technologies development will also be reviewed.

[1] Towards satellite tests combining general relativity and quantum mechanics through quantum optical interferometry: progress on the deep space quantum link, Mohageg & Kwiat & al., EPJ Quantum Technology, June 20, 2025

Massively multiplexed wide-field photon correlation sensing

Temporal photon correlations have been a crucial resource for quantum and quantum-enabled optical science for over half a century. However, attaining non-classical information through these correlations has typically been limited to a single point (or, at best, a few points) at a time. Here, we perform a massively multiplexed wide-field photon correlation measurement using a large 500×500 single-photon avalanche diode array, the SwissSPAD3. We demonstrate the performance of this apparatus by acquiring wide-field photon correlation measurements of single-photon emitters and illustrate two applications of the attained quantum information: wide-field emitter counting and quantum-enabled super-resolution imaging (by a factor of √2). The considerations and limitations of applying this technique in a practical context are discussed. Ultimately, the realization of massively multiplexed wide-field photon correlation measurements can accelerate quantum sensing protocols and quantum-enabled imaging techniques by orders of magnitude.

Paper - https://doi.org/10.1364/OPTICA.550498

Journal club

Ultrafast Kapitza-Dirac effect

Alexandr Vasilyev

Reflection of a free electron beam from a lattice formed by a standing light wave, governed by Bragg diffraction, was first proposed by Kapitza and Dirac in 1933. Despite numerous experimental efforts after the invention of lasers in the 1960s, a clear demonstration was achieved only in 2001 by Batelaan et al., using 10 ns laser pulses. In a recent study, Lin et al. used a pulsed electron beam and 60 ps laser pulses to observe the dynamic behavior of electron wave packets. This interferometric approach provides direct access to the quantum phase properties of free electrons.

[1] https://doi.org/10.1126/science.adn1555

An introduction to laser ion acceleration

Dong Jing

Nowadays, high energy ion beam plays a significant role in both scientific research and social applications, such as nuclear fusion and cancer treatment. However, traditional radio frequency (RF) accelerators require a large space to generate high energy ions due to the material ionization threshold. Ion acceleration based on laser plasma interaction makes tabletop accelerators possible. This talk will briefly introduce laser ion acceleration mechanisms, especially the widely studied target normal sheath acceleration (TNSA) mechanism. In addition, talk will briefly introduce the current status of ion acceleration in the WIS High Power Laser Lab (Prof. Malka's lab) and briefly present a particle in cell (PIC) simulation case of laser ion acceleration.
 

Robust quantum integrated photonics

Quantum information processing (QIP) relies on high-fidelity quantum state preparation and precise unitary operations; however, practical realizations face major challenges, as the permissible error per operation must remain below the fault-tolerant threshold, typically on the order of 10⁻³ to 10⁻²  in most quantum systems. Integrated photonic circuits are a leading platform for scalable QIP technologies, yet unavoidable fabrication imperfections and control inaccuracies often limit operational fidelities, preventing the realization of large-scale quantum circuits. Even small systematic errors can degrade fidelity below the fault-tolerant threshold.

A powerful approach for mitigating such errors is the composite segmentation method, originally inspired by techniques from nuclear magnetic resonance, where operations are carefully divided into segments with tailored parameters to enhance robustness. However, traditional composite techniques rely on complex-valued parameter control, whereas integrated photonic systems inherently support only real-valued parameters, making direct application of these methods not just challenging but fundamentally infeasible without new design strategies.

In this talk, I will present the detuning-modulated composite segmentation method recently developed in my lab, which enables robust quantum operations in integrated photonic platforms without requiring complex phase control. This approach corrects a wide range of errors and achieves fidelities surpassing the fault-tolerant threshold. I will share our recent numerical and experimental results demonstrating how detuning-modulated composite segmentation dramatically enhances error tolerance and achieves superior robustness in single-photon quantum gates, such as high-fidelity Hadamard gates, as well as in two-photon entangling gates within integrated quantum circuits. Our approach opens a new path toward scalable and fault-tolerant quantum integrated photonic technologies.
 

Multi-ion clocks with dynamical decoupling

Trapped ions are an ideal system for optical atomic clocks and precision tests of fundamental physics. However, the quantum projection noise of the single ion limits its stability.  Multi-ion optical clocks have an obvious potential to improve clock stability. However, their operation has so far been impeded due to the challenges of controlling the various inhomogeneous shifts that are typical to ion traps. Recently dynamic decoupling and quantum state engineering were proposed to tackle some of these challenges. In this talk, I will present the progress we have made in incorporating a dynamic decoupling scheme that suppresses the quadruple and Zeeman shifts in multi-ion clocks. I will present preliminary results for the first comparison between two multi-ion clocks, and discuss the prospect of using entanglement to enhance metrological performance.

Journal Club

Quantum interfaces with multilayered superwavelength atomic arrays

Roni Ben-Maimon

We consider quantum light-matter interfaces comprised of multiple layers of two-dimensional atomic arrays, whose lattice spacings exceed the wavelength of light. Coupling of light to one layer of such a ‘superwavelength’ array, as required in tweezer-array platforms, is considerably reduced due to scattering losses to high diffraction orders. Here we show, however, that the addition of layers can suppress these losses through destructive interference between the layers. Mapping the problem to a 1D model of a quantum interface wherein the coupling efficiency is characterized by a reflectivity, we analyze the latter by developing a geometrical optics formulation, accounting for realistic finite-size arrays. We find that optimized efficiency favors small diffraction-order angles and small interlayer separations, and that the coupling inefficiency for two layers universally scales as 1/N with the atom number per layer N. We validate our predictions using direct numerical calculations of the scattering reflectivity and the performance of a quantum memory protocol, demonstrating high atom-photon coupling efficiency. This opens the way for various applications in tweezer atomic-array platforms.

[1] arXiv:2402.06839, 2024

Terahertz emission from diamond nitrogen-vacancy centers

Ariel Smooha

Coherent light sources emitting in the terahertz range are highly sought after for fundamental research and applications. Terahertz lasers rely on achieving population inversion. We demonstrate the generation of terahertz radiation using nitrogen-vacancy centers in a diamond single crystal. Population inversion is achieved through the Zeeman splitting of the S = 1 state in 15 T, resulting in a splitting of 0.42 THz, where the middle Sz = 0 sublevel is selectively pumped by visible light. To detect the terahertz radiation, we use a phase-sensitive terahertz setup, optimized for electron spin resonance (ESR) measurements. The terahertz radiation is tunable by the magnetic field; thus, these findings may lead to the next generation of tunable coherent terahertz sources.
 

Issues and challenges of laser-plasma accelerators

The validation of theoretical models describing fundamental interactions requires increasingly large and high-performance facilities, often pushing the limits of current technological capabilities and raising environmental and economic challenges. To overcome these limitations, a conceptual breakthrough is essential.

Laser-plasma accelerators, which now hold a key position in the scientific landscape, already address numerous challenges, both in fundamental research (FEL, SF-QED) and in societal applications (security, radiotherapy). However, it remains crucial to explore their potential in the field of high-energy physics.

Quantum Science with Arrays of Alkaline-Earth Atoms

Large arrays of trapped neutral atoms have emerged over the past few years as a promising platform for quantum information processing, combining inherent scalability with high-fidelity control and site-resolved readout. In this talk, I will discuss my recent work with arrays of alkaline-earth atoms. These divalent atoms offer unique properties stemming largely from their long-lived metastable states, which form the basis of the optical atomic clock.
First, I will describe the design of a universal quantum processor based on optical clock qubits and its application in quantum metrology. I will focus on the recent demonstration of record-fidelity entangling gates and on the preparation of a cascade of different GHZ states. Second, I will discuss how to use the narrow clock transition to measure and remove thermal excitations of atoms in tweezers (a technique known as erasure conversion) which we utilize to generate hyperentangled states of motion and spin and to perform repeated ancilla-based readout. Third, I will discuss another modality of analog quantum simulation with Rydberg atom arrays.
Finally, I will briefly share some of the plans for the new apparatus we are setting up at Tel Aviv University with trapped Ytterbium atoms for quantum optics and quantum simulation.

Journal club

Mai Fabish

Quantum interference in atom-exchange reactions

Quantum coherence—a fragile and subtle phenomenon—has mostly been demonstrated in clean, isolated systems such as atoms, photons, superconductors, among others. But can such coherence survive in something as inherently chaotic and noisy as a chemical reaction? In this talk, we explore a surprising candidate: the reaction 2KRb→K2​+Rb2​, where, for the first time, the nuclear spins of KRb molecules were observed to maintain their quantum coherence and even interfere, despite becoming part of entirely different molecules.

We’ll see how this entanglement persists through the reaction and can be indirectly probed via the quantum statistics—bosonic (K2​) and fermionic (Rb2​)—of the products. This unexpected result opens new possibilities for the coherent control of chemical reactions and may offer a novel path toward using molecular systems as qubits.

Gad Horovitz

Tunable light-induced dipole-dipole interaction between optically levitated nanoparticles

When dealing with optically trapped particles, precise control over particle interactions is crucial. The experiment presented in this paper utilizes the phase coherence between optical fields to drive a light-induced dipole-dipole interaction, enabling fully controllable and nonreciprocal coupling between two nanoparticles. Additionally, the paper demonstrate how this dipole-dipole interaction can be selectively switched off, giving rise instead to an electrostatic interaction.
 

Quantum Vortices of Photons

Imagine pulling a plate across the surface of a tranquil water pool, creating a mesmerizing trail of a vortex and antivortex. In optics, vortices materialize as phase twists of the electromagnetic field. While traditionally optical vortices arise from interactions between light and matter, we discovered an extreme regime of optical nonlinearity where quantum vortices – phase dislocations in the few-photon wavefunction – form due to effective, strong interactions between the photons. These interactions are realized in a ‘quantum nonlinear optical medium’ based on ultracold Rydberg atoms. Analogous to the water pushed by the plate, the excess phase accumulating due to the photon-photon interaction gives rise to pairs of quantum vortices, vortex lines, and rings, within the photonic wavefunction. The vortex rings are warped due to warping of the underlying dispersion. The ‘conditional’ phase flip enclosed by the vortices can be used for deterministic quantum logic operations. Counter-propagating photons, in a configuration suitable for quantum gates, exhibit even longer-range, richer interactions.

Journal club

Experimental observation of a superradiant transition

Yoav Shimshi

Collective emission is a fundamental quantum optics phenomenon whose understanding is critical for controlling dissipation in upcoming quantum technologies. A key feature of the physics is the emergence of a collective atomic mode, which behaves as a single macroscopic dipole and radiates at an enhanced rate. When provided with a continuous energy source in the form of a coherent laser, this mode acquires a steady state occupation, which undergoes a phase transition into a disordered state as the driving strength increases.

In this talk we will discuss a recent observation of this transition in a cavity QED experiment. This highly controlled setting (as opposed to contemporary superradiance experiments in free space) allow for direct observation of the collective physics at experimentally accessible timescales. We will go over the basic physics needed to understand the phenomenon and discuss the different competing processes which show up in the real experiment.

Coherent quantum annealing in a programmable 2,000 qubit Ising chain
Eran Bernstein

Quantum simulation has emerged as a valuable arena for demonstrating and understanding the capabilities of near-term quantum computers. Quantum annealing has been successfully used in simulating a range of open quantum systems, both at equilibrium and out of equilibrium. This paper demonstrates for the first time a quantum simulator with coherent evolution through a quantum phase transition in the paradigmatic setting of a one-dimensional transverse-field Ising chain, using up to 2,000 superconducting flux qubits in a programmable quantum annealer (D-Wave).

I will explain and discuss the main results from the paper: Observation of the quantum Kibble–Zurek mechanism for fast annealing times (t<10ns) followed by an anti-Kibble–Zurek scaling in a crossover to the open quantum regime in slower annealing times; Verification of the quantum nature of the simulator by showing quantitative agreement to an analytic model in the measurement of kink (domain wall) statistics, as well as kink–kink correlations.

PhD defense

Attosecond science has revolutionized the ability to capture extremely fast phenomena in nature, opening a window into a new temporal regime, in which electron dynamics are observed on their natural time scale (1 as = 10-18 sec). Attosecond metrology relies on the ability to produce optical pulses, having attosecond duration, imprinting the electronic dynamics in their spectral intensity, phase and polarization state. However, the optical measurement resolves only the spectral intensity while the phase and polarization information are lost, preventing a direct access to the full information encoded in the attosecond signal.
In this talk, I will describe the application of one of the most fundamental optical schemes, interferometry, in the attosecond timescale [1,2]. Extending this scheme to the dynamic regime has unlocked new and exciting horizons in attosecond science. Time-resolved attosecond interferometry probes the evolution of an electronic wavefunction under the tunneling barrier, as it propagates in a classically forbidden region [3]. Its application to light-driven quantum systems decouples and follows the temporal evolution of individual underlying quantum paths with unprecedented precision and reveals the sub-cycle vectorial properties of transient light-matter interactions [4,5].
 

1. Azoury, D., Kneller, O., et al. Electronic wavefunctions probed by all-optical attosecond interferometry. Nature Photon 13, 54–59 (2019).
2. Azoury*, D., Kneller*, O. et al. Interferometric attosecond lock-in measurement of extreme-ultraviolet circular dichroism. Nature Photon 13, 198–204 (2019).
3. Kneller, O. et al. A look under the tunnelling barrier via attosecond-gated interferometry. Nat. Photon. 16, 304–310 (2022).
4. Kneller*, O., Mor*, C., Klimkin*, N.D. et al. Attosecond transient interferometry. Nat. Photon. 19, 134–141 (2025).
5. Kneller, O. et al. Attosecond Fourier transform spectroscopy. Submitted (2025).
 

Journal club

Quantum Frequency Combs

Chen Mor

A comb is a physical object with finely spaced teeth, designed to disentangle and organize.

Similarly, an optical frequency comb provides a spectrum of precisely spaced frequency components, enabling high-resolution spectroscopy, precision metrology, and ultrafast science. These combs have revolutionized fields such as atomic clock synchronization and molecular fingerprinting by establishing an unprecedented bridge between optical and microwave frequencies.

Quantum optical frequency combs extend these advantages into the quantum domain by leveraging coherence and quantum correlations between comb teeth. They exhibit finely resolved entanglement across a broad spectrum, enabling parallel quantum information processing, high-dimensional entanglement, and enhanced quantum sensing. By harnessing quantum coherence in frequency modes, these combs hold promise for quantum networks, secure communication, and cutting-edge quantum-enhanced technologies.

In this lecture, I will explore some of the fundamental physical principles and groundbreaking advancements shaping the future of quantum optical frequency combs science.

nanoMRI - pulsed magnetic field gradient localized at an NV center

Leora Schein-Lubomirsky

Magnetic resonance imaging (MRI) is a powerful and broadly used tool in science yet conventional methods are limited in resolution. Using similar principles one can envision achieving structural information at the nanoscale, ideally measuring the structure of a single molecule. In this talk I will present our approach to nanoMRI. We developed a controllable magnetic field gradient localized around a  single nitrogen vacancy (NV) center. I’ll present our results, demonstrating a gradient up to 1 uT / nm achieved at fields below 200 uT. In the future, this can be used to detect electrons with nanometer scale resolution and potentially enable imaging of molecules and a variety of nanostructure.

Schein-Lubomirsky, L., Mazor, Y., Stöhr, R., Denisenko, A., & Finkler, A. (2024). Pulsed magnetic field gradient on a tip for nanoscale imaging of spins. arXiv preprint arXiv:2409.17690.

Searching for parity violation in trapped chiral molecular ions

Searching for parity violation in trapped chiral molecular ions

The weak force is predicted to break the parity symmetry between left and right-handed chiral molecules, but so far the effect has eluded detection. We are developing a trapped chiral molecular ion version of the search for parity violation (PV). Our candidate molecule, CHDBrI+ is predicted to exhibit a large PV shift of a few Hz for the C-H bend vibrational transition, where the transition’s natural linewidth is narrower than the shift.

We plan to probe the PV signature in a racemic, mixed-handedness ensemble of trapped CHDBrI+, using vibrational Ramsey spectroscopy. Our newly developed ion trap is integrated with a pulsed velocity map imaging detector to probe multiple internal state populations of the molecules simultaneously by separating photo-fragment velocities. This technology will assist in overcoming the molecular complexity and help develop quantum control schemes and separation according to chirality methods for our molecule. We will discuss our progress toward creating cold CHDBrI+ by photoionization, a key ingredient in the implementation of the scheme and the current status of the experiment.

We will also discuss the advantages of using chiral molecules in searches for hypothetical internuclear forces beyond the Standard Model.

Erez et al. Phys. Rev. X 13, 041025 (2023)

Landau et al. J. Chem. Phys. 159, 114307 (2023)

Eduardus et al. Chem. Communi. 59, 14579 (2023)

Baruch et al. Phys. Rev. Research 6, 043115 (2024)

Journal club

A Millimeter-Wave Superconducting Qubit

Nitzan Kahn

Superconducting qubits are among the leading technologies driving quantum computer development. Their robustness and ability to precisely control photons in the microwave range have made them a popular choice for research groups and companies worldwide. However, their sensitivity to thermal noise necessitates the use of cooling systems that rely on rare and expensive helium-3. A recent advancement introduces superconducting qubits operating in the millimeter-wave range, around 100 GHz. These qubits are less susceptible to thermal noise, enabling operation at higher temperatures, up to 1 K, using simpler helium-4 cooling systems. This advancement bridges the gap between microwave and optical quantum technologies and opens new possibilities for quantum sensing, photon detection, and scalable quantum computing. This demonstration of controlled qubit dynamics, featuring Rabi oscillations and nanosecond-scale coherence times, can be compared to the performance of more established superconducting qubit designs studied by many groups, including those at the Weizmann Institute.

[1] Alexander Anferov, Fanghui Wan, Shannon P. Harvey, Jonathan Simon and David I. Schuster (2024). A Millimeter-Wave Superconducting Qubit. arXiv:2411.11170v1

Review on quantum phenomena in attosecond science

Shonfeld Asaf

Attosecond science has revolutionized our ability to observe and manipulate ultrafast phenomena, capturing the dynamics of electrons in their natural time scale Traditionally, the high-harmonic generation (HHG) process and its resulting broadband XUV spectrum have been treated classically, justified by the high-intensity regime. However, recent theoretical advancements have unveiled intriguing quantum aspects of light at these extreme intensities. In my talk I would delve into ref. [1] which reviews the latest developments in quantum aspects of light of high intensity light-matter interactions such as HHG. The paper provides a comprehensive review of recent theoretical and experimental achievements, examining which findings demonstrate genuinely non-classical states and which can be interpreted through classical correlations. Moreover, I’ll review experimental signs for non-classical characteristics in HHG spectra, when driven or perturbed by bright squeezed vacuum (BSV) [2][3]. These findings suggest new approaches and future applications upon the current classical understanding of light-matter interactions, bridging between strong field physics and quantum optics.

[1] Cruz-Rodriguez, L., Dey, D., Freibert, A., & Stammer, P. (2024). Quantum phenomena in attosecond science. Nature Reviews Physics, 1-14.‏

[2] Lemieux, S., Jalil, S. A., Purschke, D., Boroumand, N., Villeneuve, D., Naumov, A., ... & Vampa, G. (2024). Photon bunching in high-harmonic emission controlled by quantum light. arXiv preprint arXiv:2404.05474.‏

[3] Rasputnyi, A., Chen, Z., Birk, M., Cohen, O., Kaminer, I., Krüger, M., ... & Tani, F. (2024). High-harmonic generation by a bright squeezed vacuum. Nature Physics, 1-6.

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)