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Mode competition in nonequilibrium Rydberg gases enables the exploration of emergent many-body phases. This work leverages this emergent phase for electric field detection at room temperature. Sensitive frequency-resolved electric field measurements at very low-frequencies (VLF) are of central importance in a wide range of applications where deep-penetration is required in communications, navigation and imaging or surveying. The long wavelengths on order of 10-100 km (3-30 kHz) limit the efficiency, sensitivity, and bandwidth of compact classical detectors that are constrained by the Chu limit. Rydberg-atom electrometers are an attractive approach for microwave electric-field sensors but have reduced sensitivity at lower-frequencies. Very recent efforts to advance the standard Rydberg-atoms approach is based on DC electric-field (E-field) Stark shifting and have resulted in sensitivities between 67.9-2.2 uVcm-1Hz-1/2 (0.1-10 kHz) by fine optimization of the DC E-field. A major challenge in these approaches is the need for embedded electrodes or plates due to DC E-field Stark screening effect, which can perturb coupling of VLF signals when injected from external sources. In this article, it is demonstrated that state-of-art sensitivity (~1.6-2.3 uVcm-1Hz-1/2) can instead be achieved using limit-cycle oscillations in driven-dissipative Rydberg atoms by using a magnetic field (B-field) to develop mode-competition between nearby Rydberg states. The mode-competition between nearby Rydberg-states develop an effective transition centered at the oscillation frequency capable of supporting external VLF E-field coupling in the ~10-15kHz regime without the requirement for fine optimization of the B-field magnitude., Comment: 14 pages, 16 figures

We experimentally and theoretically study collective emission of a dense atomic ensemble coupled to a whispering-gallery-mode (WGM) in a nanophotonic microring resonator. Due to many cold atoms localized in a small volume, these trapped atoms collectively couple not only to the WGM and but also to the non-guided modes in free space. Through tuning the atom-WGM coupling and by adjusting the number of trapped atoms, we demonstrate superradiant emission to the WGM. For photon emission via the non-guided modes, our study reveals signatures of subradiance and superradiance when the system is driven to the steady-state states and the timed-Dicke states, respectively. Our experimental platform thus presents the first atom-light interface with selective collective emission behavior into a guided mode and the environment, respectively. Our observation and methodology could shed light on future explorations of collective emission with densely packed quantum emitters coupled to nanophotonic light-matter interfaces., Comment: 11 pages, 7 figures

The Axelrod approximation is widely used in astrophysical modelling codes to evaluate electron-impact excitation effective collision strengths for forbidden transitions. Approximate methods such as this are a necessity for many heavy elements with open shells where collisional data is either non existent or sparse as the use of more robust methods prove prohibitively expensive. Atomic data for such forbidden transitions are essential for producing full collisional radiative models that do not assume Local-Thermodynamic-Equilibrium (LTE). In this short work we repeat the optimization of the simple Axelrod formula for a large number of $R$-matrix data sets, ranging from Fe and Ni to the first r-process peak elements of Sr, Y and Zr, to higher Z systems Te, W, Pt and Au. We show that the approximate treatment of forbidden transitions can be a significant source of inaccuracy in such collisional radiative models. We find a large variance of the optimized coefficients for differing systems and charge states, although some general trends can be seen based on the orbital structure of the ground-state-configurations. These trends could potentially inform better estimates for future calculations for elements where $R$-matrix data is not available., Comment: Submitted to JQSRT

Scattering resonances are fundamental in science, spanning energy scales from stellar nuclear fusion to ultracold collisions. In ultracold quantum gases, magnetic Feshbach resonances have transformed quantum many-body research by enabling precise interaction control between atoms. Here, we demonstrate unprecedented control to engineer new Feshbach resonances at tunable positions via Floquet driving in a $^{6}$Li atom gas, achieved through strong magnetic field modulation at MHz frequencies. This periodic modulation creates new resonances whenever dressed molecular levels cross the atomic threshold. By adding a second modulation at twice the base frequency, we tune the asymmetry of resonance loss profiles and suppress two-body losses from Floquet heating. This technique enhances control over atomic interactions, expanding possibilities for quantum simulations of complex systems and studies of exotic quantum phases.

Coherent light-matter interactions between a quantum gas and light in a high-finesse cavity can drive self-ordering phase transitions. To date, such phenomena have involved exclusively single-atom coupling to light, resulting in coupled charge-density or spin-density wave and superradiant order. In this work, we engineer simultaneous coupling of cavity photons to both single atoms and fermionic pairs, which are also mutually coupled due to strong correlations in the unitary Fermi gas. This interplay gives rise to an interference between the charge-density wave and a pair-density wave, where the short-range pair correlation function is spontaneously modulated in space. We observe this effect by tracking the onset of superradiance as the photon-pair coupling is varied in strength and sign, revealing constructive or destructive interference of the three orders with a coupling mediated by strong light-matter and atom-atom interactions. Our observations are compared with mean-field theory where the coupling strength between atomic- and pair-density waves is controlled by higher-order correlations in the Fermi gas. These results demonstrate the potential of cavity quantum electrodynamics to produce and observe exotic orders in strongly correlated matter, paving the way for the quantum simulation of complex quantum matter using ultracold atoms.

Density Functional Theory has long struggled to obtain the exact exchange-correlational (XC) functional. Numerous approximations have been designed with the hope of achieving chemical accuracy. However, designing a functional involves numerous methodologies, which has a greater possibility for error accumulation if the functionals are poorly formulated. This study aims to investigate the performance and limitations of second-order correlation functionals within the framework of density functional theory. Specifically, we focus on three major classes of density functional approximations that incorporate second-order energy expressions: \textit{ab initio} (primarily G\"{o}rling-Levy) functionals, adiabatic connection models, and double-hybrid functionals. The principal objectives of this research are to evaluate the accuracy of second-order correlation functionals, to understand how the choice of reference orbitals and eigenvalues affects the performance of these functionals, to identify the intrinsic limitations of second-order energy expressions, especially when using arbitrary orbitals or non-canonical configurations, and propose strategies for improving their accuracy. By addressing these questions, we aim to provide deeper insights into the factors governing the accuracy of second-order correlation functionals, thereby guiding future functional development.

Resonance-enhanced multiphoton ionization (REMPI) in potassium atom is investigated within the strong coupling regime using photoelectron momentum imaging techniques. The kinetic energy distribution of the ionized electrons reveals the eigenenergies of the dressed states, which exhibit Autler-Townes (AT) splitting. This splitting is proportional to the laser field strength. Partial wave analysis of the photoelectrons angular distributions (PAD) uncovers relative phase shifts between the dressed states, shedding light on attosecond ionization time delays. The observed phase shift between the two electron wave packets generated by the AT splitting arises from the combined effects of the Coulomb phase and the quantum defect phase.

Atom-cavity systems offer unique advantages for building large-scale distributed quantum computers by providing strong atom-photon coupling while allowing for high-fidelity local operations of atomic qubits. However, in prevalent schemes where the photonic state is encoded in polarization, cavity birefringence introduces an energy splitting of the cavity eigenmodes and alters the polarization states, thus limiting the fidelity of remote entanglement generation. To address this challenge, we propose a scheme that encodes the photonic qubit in the frequency degree-of-freedom. The scheme relies on resonant coupling of multiple transverse cavity modes to different atomic transitions that are well-separated in frequency. We numerically investigate the temporal properties of the photonic wavepacket, two-photon interference visibility, and atom-atom entanglement fidelity under various cavity polarization-mode splittings and find that our scheme is less affected by cavity birefringence. Finally, we propose practical implementations in two trapped ion systems, using the fine structure splitting in the metastable D state of $\mathrm{^{40}Ca^{+}}$, and the hyperfine splitting in the ground state of $\mathrm{^{225}Ra^{+}}$. Our study presents an alternative approach for cavity-based quantum networks that is less sensitive to birefringent effects, and is applicable to a variety of atomic and solid-state emitter-cavity interfaces., Comment: 13 pages, 6 figures

We present an electrically-small Rydberg atom electric field sensor with the ability to extract the three-dimensional $k$-vector of an elliptically polarized radio frequency (rf) field. In most mediums, the $k$-vector (or wave vector) provides the direction of propagation of an electromagnetic wave. Our method uses a field vector measurement at a single point in space and is thus compatible with a sensor volume that is arbitrarily small compared to the carrier wavelength. We measure the $k$-vector of a circularly polarized signal field with average absolute errors in the polar and azimuthal angles of $33~\text{mrad}$ and $43~\text{mrad}$ respectively, and statistical noise of $1.3~\text{mrad}/\sqrt{\text{Hz}}$ and $1.5~\text{mrad}/\sqrt{\text{Hz}}$. Additionally, we characterize the performance of the sensor as a function of the ellipticity of the input field and the size of the sensing region. We find that the sensor works over a broad range of ellipticities and validate that an electrically-small sensing region is optimal., Comment: 6 pages, 4 figures

We propose that a nuclear clock based on the Th~V ion may achieve the highest accuracy among different Th ions. The Th$^{4+}$ ion has a rigid closed-shell core with zero total electron angular momentum, effectively eliminating frequency shifts in the nuclear transition caused by black-body radiation and external fields, which primarily interact with electrons. We calculate the energy shift of the nuclear clock transition frequency in $^{229}$Th due to the Coulomb field of atomic electrons. The relative frequency shift between Th~IV and Th~V ions is found to be $2.5 \times 10^{-7}$, which is twelve orders of magnitude larger than the projected uncertainty of the nuclear clock transition frequency. Additionally, we perform calculations of the energy levels and ionization potential of the Th~V ion. While all excitation energies in Th~V are significantly higher than the nuclear excitation energy ($\omega_N$), the energy intervals between certain excited states are close to $\omega_N$., Comment: 6 pages, 5 tables

Clocks based on nuclear isomer transitions promise exceptional stability and precision. The low transition energy of the Thorium-229 isomer makes it an ideal candidate, as it may be excited by a vacuum-ultraviolet laser and is highly sensitive to subtle interactions. This enables the development of powerful tools for probing new forces, which we call quintessometers. In this work, we demonstrate the potential of nuclear clocks, particularly solid-state variants, to surpass existing limits on scalar field couplings, exceeding the sensitivity of current fifth-force searches at submicron distances and significantly improving equivalence-principle tests at kilometer scales and beyond. Additionally, we highlight the capability of transportable nuclear clocks to detect scalar interactions at distances beyond $10\,$km, complementing space-based missions., Comment: 12 pages, 3 figures

The g-factors for $J = 1$, $F=3/2$, $|M_F|=3/2$ hyperfine levels of the ground electronic state $^3\Delta_1$ of the $^{232}$ThF$^+$ cation are calculated as functions of the external electric field. These calculations are necessary for the analysis of systematic effects in the experiment aimed at searching for the electron electric dipole moment.

This work presents a novel formulation for a redefinition of the second based on the weighted arithmetic mean of multiple normalized frequencies. We demonstrate that it is mathematically equivalent to the previously discussed implementation employing a geometric mean. In our reformulation, the normalization of frequencies provides the defining constants with immediate physical meaning, while maintaining the decoupling of assigned weights from the frequencies of the reference transitions. We believe that a definition based on this formulation would be significantly more accessible to both experts and non-specialists, enhancing understanding and facilitating broader acceptance. We hope that this approach will help overcome barriers to the adoption of a redefinition that effectively values all state-of-the-art atomic clocks., Comment: 2 pages, 1 figure

We present a coherent-population trapping (CPT) microcell atomic clock using symmetric auto-balanced Ramsey (SABR) spectroscopy. The pulsed SABR sequence is applied through direct current-based power modulation of the vertical-cavity surface-emitting laser, eliminating the need for an external optical shutter and enabling compatibility with fully-integrated clocks. The sequence is controlled by a single FPGA-based digital electronics board. A key aspect of proper clock operation was the implementation of a real-time tracking of the atomic signal detection window. The clock frequency dependence on laser power, microwave power, laser frequency, and timing of the detection window has been measured, obtaining sensitivity coefficients lower than those obtained with Ramsey-CPT spectroscopy. The Allan deviation of the SABR-CPT clock, based on a microfabricated cell with low-permeation glass windows, is 1.1~$\times$~10$^{-9}$ at 1~s and averages down to the low 10$^{-12}$ range at 1 day integration time. These results pave the way towards the development of Ramsey-CPT chip-scale atomic clocks with enhanced timekeeping performances., Comment: 9 pages, 7 figures

The concept of synthetic dimensions has emerged as a powerful framework in photonics and atomic physics, enabling the exploration of high-dimensional physics beyond conventional spatial constraints. Originally developed for quantum simulations in high dimensions, synthetic dimensions have since demonstrated advantages in designing novel Hamiltonians and manipulating quantum or optical states for exploring topological physics, and for applications in computing and information processing. Here we provide a comprehensive overview of progress in synthetic dimensions across photonic, atomic, and other physical platforms over the past decade. We showcase different approaches used to construct synthetic dimensions and highlight key physical phenomena enabled by the advantage of such a framework. By offering a unified perspective on developments in this field, we aim to provide insights into how synthetic dimensions can bridge fundamental physics and applied technologies, fostering interdisciplinary engagement in quantum simulation, atomic and photonic engineering, and information processing.

Modern atomic physics applications in science and technology pose ever higher demands on the precision of computations of properties of atoms and ions. Especially challenging is the modeling of electronic correlations within the configuration interaction (CI) framework, which often requires expansions of the atomic state in huge bases of Slater determinants or configuration state functions. This can easily render the problem intractable even for highly efficient atomic codes running on distributed supercomputer systems. Recently, we have successfully addressed this problem using a neural-network (NN) approach [1]. In this work, we present our Python code for performing NN-supported large-scale atomic CI using pCI [2] and other high-performance atomic codes. [1] P. Bilous, C. Cheung, and M. Safronova, Phys. Rev. A 110 042818 (2024). [2] C. Cheung, M. G. Kozlov, S. G. Porsev, M. S. Safronova, I. I. Tupitsyn, A. I. Bondarev, Comput. Phys. Commun. 308 109463 (2025)., Comment: 9 pages, 3 figures, 2 tables

We investigate the structural properties and melting behavior of two-dimensional ion crystals in an RF trap, focusing on the effects of ion temperature and trap potential symmetry. We identify distinct crystal structures that form under varying trapping conditions and temperatures through experimental observations and theoretical analyses. As the temperature increases or the trap potential becomes more symmetric, we observe a transition from a lattice arrangement to elongated ring-like formations aligned along the trap axes. Our experimental and theoretical efforts enhance our understanding of phase transitions in low-dimensional, confined systems, offering insights into the controlled formation of quantum crystals for applications in quantum simulations and many-body physics., Comment: Submitted to Entropy, under review. 8 pages, 7 figures

Cavities have driven significant advances in optical physics and quantum science, with applications ranging from lasers and spectroscopy to quantum information processing, simulation and metrology. For standard optical cavities, each eigenmode corresponds to a single, well-defined frequency. Here, we present a macroscopic optical Fabry-P\'erot cavity whose eigenmodes are coherent superpositions of two frequency modes in the VIS-NIR range. Specifically, we demonstrate strong coupling between 384 THz (780 nm) and 580 THz (516 nm) cavity modes by incorporating an intracavity $\chi^{(2)}$ crystal driven by a non-resonant optical pump at 1529 nm. Strong coupling enables us to demonstrate frequency conversion with an end-to-end, free-space conversion efficiency of 30(1)%, limited by current cavity design and internal cavity losses. We also demonstrate coupling between distinct spatial modes at the two frequencies, extending coherent control to the spatial basis. In conjunction with improved resonator design and low-loss nonlinear crystals, we anticipate a factor of $>$50 increase in two-mode-cooperativity for stronger coupling and near-unity conversion efficiency at low pump powers. This platform opens new avenues for cavity-QED experiments, with potential applications spanning cavity-mediated interactions between distinct atomic species, interconnects for quantum networking and modular computing, and spatially multimode cavity physics., Comment: 12 pages, 4 main figures, 3 supplementary figures

We explore how the spectral phase of atto\-second pulse trains influences the optical cross section in transient absorption (TA) spectroscopy. The interaction of extreme ultraviolet (XUV) and time-delayed near-infrared (NIR) fields with an atomic or molecular system governs the dynamics. As already shown in RABBITT experiments, the spectral phase of the XUV pulses can be extracted from the photoionization spectrum as a function of the time delay. Similarly, this XUV phase imprints itself on delay-dependent optical cross-section oscillations. With a perturbative analytical approach and by simulating the quantum dynamics both in a few-level model and via solving the time-dependent Schr\"odinger equation for atomic hydrogen, we reveal the similarity between the spectral phase in RABBITT and TA spectroscopy., Comment: 7 pages, 5 figures

We explored a distinct mechanism for matter creation via electron-positron pair production during bound-bound transitions in the deexcitation of one-muon ions. For ions with nuclear charges $Z\geq24$, transitions from low-lying excited states to the 1s-muon state can lead to the production of electron-positron pairs. We show that the Breit interaction determines the transition probabilities for states with nonzero orbital momentum. Although the $2s$ state is metastable, pair production arises mainly from the decay of the $2p$ states. Thus, the Breit interaction governs electron-positron pair production in bound-bound muon transitions. This process offers a unique opportunity to explore quantum electrodynamics in strong fields, as well as a class of nonradiative transitions involving electron-positron pair production., Comment: 5 pages, 1 figure

The DESIRE project aims to test chameleon field theories as potential candidates for dark energy. The chameleon field is a light scalar field that is subject to screening mechanisms in dense environments making them hardly detectable. The project is designed to overcome this challenge. To this end, a specially designed source mass generates periodic gravitational and chameleon potentials. The design of the source mass allows for adjustment of the amplitude and periodicity of the gravitational potential while keeping the chameleon potential unchanged. The periodicity of the potentials makes them distinguishable from the environment and allows for resonant detection using multiloop atom interferometry under microgravity conditions.

We present new measurements of quantum defects and core polarizabilities in cesium ($^{133}$Cs), based on transition frequency measurements between Rydberg states ($14 \leq n \leq 38$) obtained through terahertz (THz) and radio-frequency spectroscopy in a thermal atomic vapor. %By detuning resonant fields coupling neighbouring Rydberg states, we observe a detuning-dependent asymmetry in the line shape which can be used to extract the frequency of the transition. We perform a global fitting of our measurements to extract quantum defects of the $s_{1/2}$, $p_{1/2}$, $p_{3/2}$, $d_{3/2}$, $d_{5/2}$, $f_{5/2}$, $f_{7/2}$, $g_{7/2}$ and $g_{9/2}$ electronic states. Transitions between high angular momentum states ($4 \leq \ell \leq 8$) were measured to extract the Cs$^{+}$ dipole and quadrupole polarizabilities. We find $\alpha_{d} = 15.729(18)$ $a_{0}^{3}$ and $\alpha_{q} = 76.3(1.9)$ $a_{0}^{5}$ respectively. Using these results, and accounting for the covariances between parameters in the global fit, the energies for $n\ell_{j}$ Rydberg states can be estimated to a precision of a few MHz or less.

The coherence time of an optically trapped neutral atom is a crucial parameter for quantum technologies. We found that optical dipole traps with higher-order spatial forms inherently offer lower decoherence rates compared to those with lower-order spatial forms. We formulated the decoherence rate caused by the variance of the differential energy shift and photon jumping rate. Then, we constructed blue-detuned harmonic and quartic optical dipole traps, and experimentally investigated the coherence time of a trapped single cesium atom. The experimental results qualitatively verified our theory. Our approach provides a novel method to enhance the coherence time of optically trapped neutral atoms., Comment: 4 pages, 3 figures

High-sensitivity measurements of the microwave electric field are important in applications of communication and metrology. \replaced{The sensitivity of traditional Rydberg superheterodyne receivers in free space is effectively determined by the signal-to-noise ratio (SNR), which is often considered equivalent to sensitivity in practical sensing applications.}{The sensitivity of the traditional Rydberg superheterodyne receivers in free space is limited by signal-to-noise contrast.} In this work, we demonstrate a cavity-enhanced receiver, where an optical cavity significantly amplifies the interaction between the probe light and cesium atoms, which substantially improves the signal-to-noise ratio via enhancing the expansion coefficient \( \kappa \). \added{Here, $\kappa$ is the edge slope of the single peak obtained by fitting the double-peak EIT-AT spectrum, characterizing the response of the probe light to the frequency detuning of the coupling laser.}The sensitivity is thus boosted by a factor of approximately 19 dB. This study highlights the pivotal role of optical cavities in advancing Rydberg-based detection systems, offering a promising approach for high-sensitivity microwave electric field measurements., Comment: 7 pages, 3 figures

We report the phenomena of electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) using two identical beams in rubidium atomic vapor. The {\Lambda}-type EIT configuration is employed to examine the EIT spectrum for the D1 line in 87Rb F=2 characteristics16 by varying parameters such as frequency detuning, Iprobe/Ipump, the total power of probe and pump beam. Notably, the pump beam is also investigated in this process, which has not been previously studied. We study the effect of of the phase between the two applied fields and find that EIA and EIT can transform into each other by adjusting the relative phase. These finding may have applications in light drag or storage, optical switching, and sensing.

We experimentally demonstrate an unambiguous quantum state discrimination of two qubit states under a non-Hermitian Hamiltonian with parity-time-reversal ($\mathcal{PT}$) symmetry in a single trapped $^{40}$Ca$^+$ ion. We show that any two non-orthogonal states can become orthogonal subjected to time evolution of a $\mathcal{PT}$-symmetric Hamiltonian in both the $\mathcal{PT}$-symmetry preserving and broken regimes, thus can be discriminated deterministically. For a given pair of candidate states, we show that the parameters of the Hamiltonian must be confined in a proper range, within which there exists an optimal choice to realize quantum brachistochrone for the fastest orthogonalization. Besides, we provide a clear geometric picture and some analytic results to understand the main conclusions. Our work shows a promising application of non-Hermitian physics in quantum information processing., Comment: 6 pages, 4 figures

Errors associated with qubit loss constitute an important source of noise in many quantum hardware systems, particularly in neutral atom quantum computers. We develop a theoretical framework to handle these errors in logical algorithms, incorporating decoding techniques and circuit-level optimizations. Focusing on experimentally-motivated error models, we introduce a delayed-erasure decoder which leverages information from state-selective readout to accurately correct loss errors, even when their precise locations are unknown. Our decoding technique is compatible with a wide range of quantum error correction codes and general logical circuits. Using this decoder, we identify strategies for detecting and correcting atom loss based on the logical circuit structure. For deep circuits with a large number of gate layers prior to logical measurements, we explore methods to integrate loss detection into syndrome extraction with minimal overhead, identifying optimal strategies depending on the qubit loss fraction in the noise. In contrast, many algorithmic subroutines involve frequent gate teleportation, shortening the circuit depth before logical measurement and naturally replacing qubits without additional overhead. We simulate such a teleportation-based algorithm, involving a toy model for small-angle synthesis and find a significant improvement in logical error rates as the loss fraction increases, with loss handled solely through teleportation. These results provide a path forward for advancing large-scale fault tolerant quantum computation in systems with loss errors., Comment: 12 + 18 pages, 7 + 16 figures

Hybrid quantum systems with different particle species are fundamental in quantum materials and quantum information science. In this work, we demonstrate that Hamiltonian learning in hybrid spin-boson systems can achieve the Heisenberg limit. Specifically, we establish a rigorous theoretical framework proving that, given access to an unknown hybrid Hamiltonian system, our algorithm can estimate the Hamiltonian coupling parameters up to root mean square error (RMSE) $\epsilon$ with a total evolution time scaling as $T \sim \mathcal{O}(\epsilon^{-1})$ using only $\mathcal{O}({\rm polylog}(\epsilon^{-1}))$ measurements. Furthermore, it remains robust against small state preparation and measurement (SPAM) errors. In addition, we also provide an alternative algorithm based on distributed quantum sensing, which significantly reduces the maximum evolution time per measurement. To validate our method, we apply it to the generalized Dicke model for Hamiltonian learning and the spin-boson model for spectrum learning, demonstrating its efficiency in practical quantum systems. These results provide a scalable and robust framework for precision quantum sensing and Hamiltonian characterization in hybrid quantum platforms.

Nonequilibrium dynamics are closely related to various fields of research, in which vastly different phases emerge when parameters are changed. However, it is difficult to construct nonequilibrium systems that have sufficiently tunable controllable parameters. Using microwave field coupling induced optical bistability, Rydberg gases exhibit a range of significantly different optical responses. In conjunction with electromagnetically induced transparency, the microwave coupling can create versatile nonequilibrium dynamics. In particular, the microwave coupling of two Rydberg states provides an additional handle for controlling the dynamics. And the microwave-controlled nonequilibrium phase transition has the potential to be applied in microwave field measurement. This study opens a new avenue to exploring bistable dynamics using microwave-coupled Rydberg gases, and developing quantum technological applications., Comment: 10 page,5 figure

We investigate the spontaneous parity-time (PT )-symmetry breaking and spectral properties of a PT symmetric quantum kicked rotor under resonance conditions. At resonance, the QKR reduces to a finite-dimensional system. In the localized regime, we find that increasing the non-Hermitian parameter always induces a transition from a phase where the states exhibit PT symmetry to one where PT symmetry is spontaneously broken. In contrast, in the delocalized regime, the existence of such a transition depends on whether the reduced system is PT symmetric. If the reduced system is not PT symmetric, PT symmetry remains in the broken phase regardless of the non-Hermitian parameter. We further analyze the spectral statistics of the system in the delocalized regime. For real energy spectra, the level-spacing distribution transitions from Wigner-Dyson statistics, associated with the Gaussian orthogonal ensemble, to Poisson statistics as the non-Hermitian parameter increases, with the intermediate regime well described by the Brody distribution. For complex spectra, the level-spacing ratios and distributions are governed by time-reversal symmetry. The spectral statistics align with predictions for non-Hermitian random matrix ensembles in classes AI{\dag} and A, depending on the presence or absence of time-reversal symmetry. Our results provide insights into the spectral characteristics of non-Hermitian quantum chaotic systems and their connection to PT symmetry., Comment: 7 pages with 7 figures

High-order harmonic generation (HHG) in gases is inherently inefficient, prompting ongoing efforts to enhance the output of coherent table-top XUV sources. In this study, we investigate the influence of the laser pulse duration on HHG using a compact post-compression method featuring a bulk multi-pass cell. This setup enables tunable Fourier-limited pulse durations as short as 42 fs. We examine the HHG yield as a function of the laser intensity for pulse durations ranging from 42 fs to 180 fs while maintaining identical focusing conditions and generating medium. Our findings reveal that, for a given intensity, there exists an optimum pulse duration -- not necessarily the shortest -- that maximizes conversion efficiency. This optimum pulse duration increases as the intensity decreases. The experimental results are corroborated by numerical simulations, which show the dependence of HHG yield on the duration and peak intensity of the driving laser and underscore the importance of the interplay between light-matter interaction and phase-matching in the nonlinear medium. Our conclusion allows us to understand why HHG could be demonstrated in 1988 with pulses as long as 40 ps pulses and intensities of only a few $10^{13}$ W/cm${^2}$., Comment: 10 pages, 7 figures

We experimentally realize a new cavity quantum electrodynamics (QED) platform with defect-free single-atom array strongly coupled to an optical cavity. The defect-free single-atom array is obtained by rearranging a probabilistically loaded one-dimensional (1D) optical tweezer array with dimensions of $1 \times 40$. The atom array is enclosed with two cavity mirrors, which compose a miniature optical Fabry-P{\'e}rot cavity with cavity length of 1.15 mm. By precisely controlling the position of the atom array, we demonstrate uniform and strong coupling of all atoms in the array with the optical cavity. The average coupling strength between the single atom and the cavity is 2.62 MHz. The vacuum Rabi splitting spectra for single-atom arrays with atom number $N$ changing from 3 to 26 are measured. Thus, the collective enhancement of the coupling strength with ${\sqrt N}$-dependence for multiple atoms is validated at the single atom level. Our system holds significant potential for establishing the foundation of distributed quantum computing and advancing fundamental research in many-body physics., Comment: 6 pages, 5 figures

The Quantum Phase Difference Estimation (QPDE) algorithm, as an extension of the Quantum Phase Estimation (QPE), is a quantum algorithm designed to compute the differences of two eigenvalues of a unitary operator by exploiting the quantum superposition of two eigenstates. Unlike QPE, QPDE is free of controlled-unitary operations, and is suitable for calculations on noisy intermediate-scale quantum (NISQ) devices. We present the implementation and verification of a novel early fault-tolerant QPDE algorithm for determining energy gaps across diverse spin system configurations using NISQ devices. The algorithm is applied to the systems described by two and three-spin Heisenberg Hamiltonians with different geometric arrangements and coupling strengths, including symmetric, asymmetric, spin-frustrated, and non-frustrated configurations. By leveraging the match gate-like structure of the time evolution operator of Heisenberg Hamiltonian, we achieve constant-depth quantum circuits suitable for NISQ hardware implementation. Our results on IBM quantum processors show remarkable accuracy ranging from 85\% to 93\%, demonstrating excellent agreement with classical calculations even in the presence of hardware noise. The methodology incorporates sophisticated quantum noise suppression techniques, including Pauli Twirling and Dynamical Decoupling, and employs an adaptive framework. Our findings demonstrate the practical viability of the QPDE algorithm for quantum many-body simulations on current NISQ hardware, establishing a robust framework for future applications.

It has been demonstrated that the Rydberg criticality in a many-body atomic system can enhance the measurement sensitivity of the microwave electric field by increasing the Fisher information. In our previous work, we proposed and experimentally verified that the Fisher information near the critical point can be increased by more than two orders of magnitude with the Rydberg atoms coupled with an optical cavity compared with that in free space. Here we demonstrate the precision measurement of the microwave electric field by cavity-enhanced critical behavior. We show that the equivalent measurement sensitivity of the microwave electric field can be enhanced by an order of magnitude compared with that in free space. The obtained sensitivity can be enhanced to 2.6 nV/cm/Hz$^{1/2}$., Comment: 5 pages, 4 figures

We measured the $g$-factor of the excited state $^3\text{P}_1$ in $\text{Ca}^{14+}$ ion to be $g = 1.499032(6)$ with a relative uncertainty of $4\times10^{-6}$. The magnetic field magnitude is derived from the Zeeman splitting of a $\text{Be}^+$ ion, co-trapped in the same linear Paul trap as the highly charged $\text{Ca}^{14+}$ ion. Furthermore, we experimentally determined the second-order Zeeman coefficient $C_2$ of the $^3\text{P}_0$ - $^3\text{P}_1$ clock transition. For the $m_J=0\rightarrow m_{J'}=0$ transition, we obtain $C_2 = 0.39\pm0.04\text{HzmT}^{-2}$, which is to our knowledge the smallest reported for any atomic transition to date. This confirms the predicted low sensitivity of highly charged ions to higher-order Zeeman effects, making them ideal candidates for high-precision optical clocks. Comparison of the experimental results with our state-of-the art electronic structure calculations shows good agreement, and demonstrates the significance of the frequency-dependent Breit contribution, negative energy states and QED effects on magnetic moments.

We report improved absolute frequency measurement of the $^{1}$S$_{0}-^{3}$P$_{0}$ transition of $^{171}$Yb at National Metrology Institute of Japan (NMIJ) by comparing the $^{171}$Yb optical lattice clock NMIJ-Yb1 with 13 Cs primary frequency standards via International Atomic Time from August 2021 to May 2023. The measured absolute frequency is 518 295 836 590 863.62(10) Hz with a fractional uncertainty of $1.9\times10^{-16}$, in good agreement with the recommended frequency of $^{171}$Yb as a secondary representation of the second. This uncertainty is 2.6 times lower than our previous measurement uncertainty, and slightly lower than any uncertainties of the absolute frequency measurements of $^{171}$Yb that have so far been reported by other institutes. We also estimate correlation coefficients between our present and previous measurements, which is important for updating the recommended frequency.

We investigate the time-dependent evolution of the dipole phase shift induced by strong-field ionization (SFI) using attosecond transient absorption spectroscopy (ATAS) for time-delays where the pump-probe pulses overlap. We study measured and calculated time-dependent ATA spectra of the ionic 4d-5p transition in xenon, and present the time-dependent line shape parameters in the complex plane. We attribute the complex, attosecond-scale dynamics to the contribution of three distinct processes: accumulation of ionization, transient population, and reversible population of excited states arising from polarization of the ground state., Comment: 6 pages, 6 figures. All data in the manuscript and the minimal model can be found in the GitHub repository, see https://github.com/lhutcheson/dipole_response.git

A novel non-invasive microscopy technique for imaging and sizing of folded DNA molecules with the use of photovoltaic tweezers and phase-sensitive detection is elaborated and realized. This novel method is compared with the state-of-the-art method of visualization of DNA molecules by fluorescent microscopy technique which requires the labeling of the DNA by dye molecules. The advantage of the novel method is no requirement for the incubation of DNA with a fluorescent label, as well as the simultaneous observation of the light-induced inside the crystal refractive lattice (i.e. photovoltaic field configuration) and the trapped micro-objects by the phase-contrast method. The suggested novel method provides the accurate measurement of the size and shape of the folded DNA molecules as well as the determination of the charged or neutral nature of the trapped bio-objects by their disposition relative to the lattice fringes. We demonstrate that the labeling of DNA causes an overestimation of the molecular size. The method can be extended to the other bio-objects. The high-performance photovoltaic tweezers operating in an autonomous regime as lab-on-a-chip devices are promising for applications in integrated optics, microscopy, micro- and nanoelectronics, and biotechnology., Comment: 18 pages, 8 figures, 38 references

Exceptional points are remarkable features of open quantum systems, such as photo-ionizing or photo-dissociating molecules, amplified or dissipated light states in photonic structures, and many others. These points mark spectral degeneracies in a system's parameter space where the eigenstates become non-orthogonal, enabling precise control over decay rates, topological transitions in parity-time (PT)-symmetric systems, or boosting the system's sensitivity to external stimuli. Here we show that exceptional points can be enantiosenstive, enabling a new type of control over topological and chiral properties of non-Hermitian open chiral systems. We apply the concept of enantio-sensitive exceptional points to demonstrate a broad range of phenomena, from enantiosensitive topological population transfer, to lifetime branching in resonant photo-decay of chiral molecules, to enhanced chiral sensing in optical fibers. Our results combine high enantiosensitivity with topological robustness in chiral discrimination and separation, paving the way for new approaches in the control of non-Hermitian and chiral phenomena.

From biology and astronomy to quantum optics, there is a critical need for high frame rate, high quantum efficiency imaging. In practice, most cameras only satisfy one of these requirements. Here we introduce interlaced fast kinetics imaging, a technique that allows burst video acquisition at frame rates up to 3.33 Mfps using a commercial EMCCD camera with single-photon sensitivity. This approach leverages EMCCD's intrinsic fast row transfer dynamics by introducing a tilted lens array into the imaging path, creating a spatially distributed grid of exposed pixels, each aligned to its own column of the sensor. The remaining unexposed pixels serve as in-situ storage registers, allowing subsequent frames to be captured after just one row shift operation. Our interlaced fast kinetics camera maintains 50% contrast for square wave intensity modulation frequencies up to 1.61 MHz. We provide benchmarks of the video performance by capturing two dimensional videos of spatially evolving patterns that repeat every 2$\mu$s, with spatial resolution of 11$\times$15 pixels. Our approach is compatible with commercial EMCCDs and opens a new route to ultra-fast imaging at single-photon sensitivity with applications from fast fluorescence imaging to photon correlation measurement., Comment: 16 pages, 11 figures

We study discrete time crystal formation in a system driven periodically by an oscillating atomic mirror, consisting of two distinct ultracold atomic clouds in the presence of a gravitational field. The intra-species interactions are weak and attractive, while the inter-species interactions are infinitely strong and repulsive. The clouds are arranged in a one-dimensional stack, where the bottom cloud bounces on an oscillating atomic mirror, which effectively acts as a driving force for the upper cloud due to the infinite inter-species repulsion. Using a Jastrow-like variational ansatz for the many-body wavefunction, we show that sufficiently strong attractive intra-species interactions drive each subsystem to spontaneously break discrete time translation symmetry, resulting in the formation of a complex discrete time crystal evolving with a period different than the driving period. Since the bottom cloud serves as the effective periodic driving for the upper cloud, this leads to a cascade of spontaneous symmetry breaking. With increasing intra-species interactions, we first observe a pronounced effect of spontaneous time translation symmetry breaking in the upper cloud, followed by a similar effect in the lower atomic cloud., Comment: 7 pages, 3 figures

An analysis of the measured rovibrational transitions is carried out for the 12C32S2 isotopologue of carbon disulfide. Data from 21 sources is extracted and validated using a consistent set of standard linear molecule quantum numbers. A corrected list of 8714 CS2 transitions forms the input to a Measured Active Rotational-Vibrational Energy Levels (MARVEL) procedure, generating 4279 empirical rovibrational energy levels across 138 bands of 12C32S2. Results are compared to the recent NASA Ames line list. While the agreement is generally good, issues are identified with the energy levels of some states, notably those with high values of the v2 bending quantum number., Comment: Accepted for publication in the Journal of Molecular Spectroscopy

Coulomb crystals, ordered structures of cold ions confined in ion traps, find applications in a variety of research fields. The number and temperature of the ions forming the Coulomb crystals are two key attributes of interest in many trapped-ion experiments. Here, we present a fast and accurate approach of determining these attributes from fluorescence images of the ions based on convolutional neural networks (CNNs). In this approach, we first generate a large number of images of Coulomb crystals with different ion numbers and temperatures using molecular-dynamics simulations and then train CNN models on these images to classify the desired attributes. The classification performance of several common pre-trained CNN models was compared in example tasks. We find that for crystals with ion numbers in the range 100-299 and secular temperatures of 5-15 mK, the best-performing model can discern number variations on the level of one ion with an accuracy of 93% and temperature variations by 1 mK with an accuracy of 92%. Since the trained model can be directly integrated into experiments, in-situ determination of these attributes can be realized in a non-invasive fashion, which has the potential to greatly facilitate the analysis and control of trapped ions in real time.

Electron-ion collision spectroscopy at heavy-ion storage rings aims at precision measurements of resonance features that occur in the cross sections of electron collision processes such as electron-impact ionization of ions or electron-ion recombination. As part of the international FAIR project, the low-energy ion storage ring CRYRING@ESR has been coupled with the heavy-ion accelerators operated by the GSI Helmholtz Center for Heavy-Ion Research in Darmstadt, Germany. This has created a new opportunity for stringent tests of strong field quantum electrodynamics by electron-ion collision spectroscopy of heavy few-electron ions. The present contribution provides details of the electron-ion collision spectroscopy setup at CRYRING@ESR and of the associated data-analysis procedures along with first results for nonresonant and resonant recombination of berylliumlike lead ions. For nonresonant recombination a recombination rate enhancement factor of 3.5 is found at zero electron-ion collision energy. For resonant recombination there is excellent agreement with recent theoretical results when these are shifted by 340~meV in energy., Comment: 10 pages, 9 figures, 1 table

The integration of quantum computers and sensors into a quantum network opens a new frontier for quantum information science. We demonstrate high-fidelity entanglement between ytterbium-171 atoms -- the basis for state-of-the-art atomic quantum processors and optical atomic clocks -- and optical photons directly generated in the telecommunication wavelength band where loss in optical fiber is minimal. We entangle the nuclear spin of the atom with a single photon in the time bin basis, and find an atom measurement-corrected (raw) atom-photon Bell state fidelity of $0.950(9)\pm0.005(3)_\text{bound}$ ($0.90(1)\pm0.014(3)_\text{bound}$). Photon measurement errors contribute $\approx0.037$ to our infidelity and can be removed with straightforward upgrades. Additionally, by imaging our atom array onto an optical fiber array, we demonstrate a parallelized networking protocol that can provide an $N$-fold boost in the remote entanglement rate. Finally, we demonstrate the ability to preserve coherence on a memory qubit while performing networking operations on communication qubits. Our work is a major step towards the integration of atomic processors and optical clocks into a high-rate or long-distance quantum network., Comment: 7 pages, 5 figures in main text; 23 pages total

We present systematic relativistic many-body calculations of multipole transition properties for singly charged aluminum ion (Al II) using a method that combines the configuration interaction and many-body perturbation theory (CI+MBPT). Our calculations cover the 103 lowest energy levels in Al II. For five key low-lying configurations (3s2 1S0, 3s3p 3P0, 3s3p 3P1, 3s3p 3P2, 3s3p 1P1), we tabulate the transition wavelengths, reduced matrix elements, transition probabilities, and oscillator strengths for about 400 electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions arising from these levels. Our calculated values agree well with available experimental data and other high-precision theoretical calculations, with typical deviations on the order of 1%. Notably, we report over 80% of these transition lines as previously unreported, significantly expanding the existing spectroscopic database for Al II. These results can serve as a valuable reference resource for ongoing precision quantum metrology as well as astrophysical spectroscopy involving Al II ion.

We demonstrate the effect of Zeeman and hyperfine optical pumping and transverse laser cooling of a dysprosium (Dy) atomic beam on the $4f^{10}6s^2(J = 8) \rightarrow 4f^{10}6s6p(J = 9)$ transition at 421.291 nm. For $^{163}$Dy, an electro-optic modulator is used to generate five frequency sidebands required to pump the atoms to the $F = 10.5$ ground state hyperfine level and the light polarization is chosen to pump the atoms to the $m_F = 10.5$ Zeeman sublevel. The atoms are simultaneously laser-cooled using a standing wave orthogonal to the atomic beam. The resulting polarized and cooled atomic beam will be used in fundamental physics experiments taking advantage of the accidental degeneracy of excited states in Dy including the ongoing measurement of parity violation in this system., Comment: 8 pages, 10 figures

Time-domain interferometry is an important principle in Fourier transform (FT) and nonlinear femto- to attosecond spectroscopy. To optimize the resolution and sensitivity of this approach, various interferometer stabilization schemes have been developed. Among them, acousto-optical phase modulation (AOPM) of the interferometer arms combined with phase-synchronous lock-in detection has proven as a particular sensitive technique. However, the acousto-optical modulators (AOMs), required for this technique, introduce several disadvantages. Here, we demonstrate an alternative phase modulation scheme which omits AOMs, termed PM scheme here. As a benchmark, we directly compare the performance between the PM and the AOPM scheme in a linear FT spectroscopy experiment and find comparable sensitivity in both approaches.

Strongly driven nonlinear systems are frequently encountered in physics, yet their accurate control is generally challenging due to the intricate dynamics. In this work, we present a non-perturbative, semi-analytical framework for tailoring such systems. The key idea is heuristically extending the Floquet theory to nonlinear differential equations using the Harmonic Balance method. Additionally, we establish a novel constrained optimization technique inspired by the Lagrange multiplier method. This approach enables accurate engineering of effective potentials across a broader parameter space, surpassing the limitations of perturbative methods. Our method offers practical implementations in diverse experimental platforms, facilitating nonclassical state generation, versatile bosonic quantum simulations, and solving complex optimization problems across quantum and classical applications.

We study the stability of bound states of antiprotons in close proximity to the atomic nucleus. Using experimental data from X-ray spectroscopy measurements of antiprotonic atom transitions, we tune a minimal theoretical framework and estimate parameter ranges where the strong or electromagnetic decay channels govern the stability of the deepest bound states. In this way, we present an overview of the dominant decay mechanism of antiprotonic orbits for a given principle quantum number, which may be useful for future spectroscopic experiments on antiprotonic atoms.