Bose-Einstein condensates (BECs) of neutral atoms constitute an important quantum system for fundamental research and precision metrology. Many applications require short preparation times of BECs, for example, for optimized data acquisition rates in scientific applications, and reduced dead times and improved bandwidths for atomic quantum sensors. Here, we report on the generation of rubidium BECs with a repetition rate of more than $2\mathrm{Hz}$. The system relies on forced evaporation in a dynamically adjusted optical potential, which is created by the spatial modulation of laser beams. Our system provides a versatile source of the ubiquitous rubidium BECs, and promotes their exploitation for high-precision atom interferometers.

Electron emission (EE) from insulating polystyrene nanoparticles induced by a single collision with swift ions is investigated. The ions electronic stopping powers explored range from 35 ev/nm to 2.3 kev/nm. A cross-beam experiment is developed to measure charge-state distributions of nanoparticles of 100 nanometer radius. The proportionality between the EE and the stopping power observed when measured using grounded conductive foils is no longer fulfilled. We perform a complementary analysis of nanoparticle charging by using Monte Carlo simulations. We emphasize the role of particle charging by taking into account the effect of the holes on the dynamics of electron emission. The resulting charging effect can be as large as two orders of magnitude for the highest stopping power. This explains rather well the experimentally observed strong sublinearity of electron emission with stopping power. As the nanoparticle size decreases, the simulation suggests that the charging effect diminishes, but remains significant for large stopping power.

Characterizing the set of distributions that can be realized in the triangle network is a notoriously difficult problem. In this work, we investigate inner approximations of the set of local (classical) distributions of the triangle network. A quantum distribution that appears to be nonlocal is the elegant joint measurement (EJM) [Entropy 21, 325 (2019)], which motivates us to study distributions having the same symmetries as the EJM. We compare analytical and neural-network-based inner approximations and find a remarkable agreement between the two methods. Using neural network tools, we also conjecture network Bell inequalities that give a trade-off between the levels of correlation and symmetry that a local distribution may feature. Our results considerably strengthen the conjecture that the EJM is nonlocal.

Nonclassical mechanical states, as vital quantum resources for exploring macroscopic quantum behavior, have wide applications in the study of the fundamental quantum mechanics and modern quantum technology. In this work, we propose a scheme for deterministically generating nonclassical mechanical states in cavity optomechanical systems. By working in the eigenrepresentation of the nonlinear optomechanical systems, we identify the carrier-wave resonance conditions and seek optimal driving pulses for state preparations. Concretely, we employ the reinforcement learning method to optimize the pulsed driving fields, effectively suppressing the undesired transitions induced by both the pulsed driving fields and dissipations. This approach enables the high-fidelity preparation of phononic Fock states and superposed Fock states in the single-resonator optomechanical systems, as well as two-mode entangled states in the two-resonator optomechanical systems. The statistical properties of the generated states are also examined. Our results create an opportunity for quantum state engineering in quantum optics and quantum information science via reinforcement learning.

The study of the long-time dynamics of quantum systems can be a real challenge, especially in systems such as ultracold gases, where the required timescales may be longer than the lifetime of the system itself. In this Letter, we show that it is possible to access the long-time spin dynamics of a strongly repulsive atomic gas mixture in shorter times. The shortcut-to-dynamics protocol that we propose does not modify the fate of the observables, but effectively jumps ahead in time without changing the system's inherent evolution. Just as the next-chapter button in a movie player that allows to quickly reach the part of the movie one wants to watch, it is a leap into the future.

We solve the problem of a dimer moving on a spherical surface and find that its binding energy and wave function are sensitive to the total angular momentum. The dimer gets squeezed in the direction orthogonal to the center-of-mass motion and can qualitatively change its geometry from two dimensional to one dimensional. These results suggest that combining the curved geometry with finite angular momentum may give rise to qualitatively new many-body phenomena in ultracold shell-shaped gases.

Macroscopic QED (MQED) is the field theory for computing quantum electromagnetic effects in dispersive media. Here, we extend MQED to treat time-varying, dispersive media. For a time-dependent Drude model, we find that the expected replacement $\varepsilon \left(\omega \right)\to \varepsilon (t,\omega )$ within standard MQED does not lead to a permittivity that is similar to that of the classical time-dependent Drude model and can lead to large polarization currents, becoming singular in the limit of a step change in carrier density. We show this unwanted behavior can be removed through instead modifying the reservoir dynamics, quantizing the resulting theory and finding the nonequilibrium, time-varying noise currents, which exhibit extra correlations due to temporal reflections within the material dynamics.

Alkali-metal–noble-gas comagnetometers are precision probes well suited for tests of fundamental physics and inertial rotation sensing, combining the high sensitivity of the spin-exchange-relaxation-free magnetometers with inherent suppression of magnetic field noise. Past versions of the device utilizing continuous-wave optical pumping are sensitive to rotation and anomalous spin couplings along a single axis perpendicular to the plane spanned by the orthogonal pump and probe laser beams. These devices are susceptible to light shifts in the alkali atoms, and to power and beam pointing fluctuations of both the probe and pump lasers, the latter of which is a dominant source of $1/f$ noise. In this work, we model and implement an approach to alkali-metal–noble-gas comagnetometers using pulsed optical pumping. After each pump laser pulse, an off-resonance probe beam measures the precession of noble-gas-spins-coupled alkali spins via optical rotation in the dark, thus eliminating effects from pump laser light shift and power fluctuations. Performing nonlinear fitting on the sinusoidal transient signal with a proper phase enables independent and simultaneous measurement of signals along two orthogonal axes in the plane perpendicular to the pump beam. Effects from beam pointing fluctuations of the probe beam in the pump-probe plane are fundamentally eliminated, and signal response to pump beam pointing fluctuations is suppressed by compensation from noble-gas nuclear spins.

We study superfluid drag in the two-component Bose-Hubbard model with infinitely strong repulsive interactions. In this system, all transport is mediated by the motion of empty sites, or “holes,” and it is hard to move one component without moving the other. We demonstrate, with a combination of analytic and numeric techniques, that the motion of holes leads to strong dissipationless coupling between currents in the two components. This behavior is attributable to polaronic correlations that emerge in the presence of spin currents, which can be observed in experiments. We derive a closed-form expression for the coupling on various lattices in arbitrary spatial dimensions, which we verify through numerical simulations on two-dimensional lattices.

Quantum key distribution (QKD) allows remote parties to share secret keys with proven security. In practice, optical schemes based on the Faraday mirror and Sagnac loop are widely used in QKD systems to improve the stability of QKD systems. In these schemes, light transmits bidirectionally in the optical path, compensating the effects caused by the environment automatically. However, due to the finite extinction ratio of the light source, these schemes will modulate the leaked light between the signal pulses, resulting in time-dependent side channels. Here, we provide a comprehensive experimental study of the security for practical QKD with time-dependent side channels. We demonstrate the amount of information leakage from the encoding modules using a Faraday mirror and Sagnac loop in a high-speed QKD system. Based on experimental results, we analyze the security risks and the corresponding countermeasures.

Weakly bound systems provide possibilities to study nonlocal electronic decay processes, which present unique physical and chemical properties. Here we report the experimental observation of a nonlocal decay process, i.e., nonadiabatic-coupling-mediated charge transfer (NCMCT), in argon dimer. This process can be effectively produced and manipulated by the double electron capture in low-charge-state oxygen ion collisions. Compared to other common decay mechanisms of ${\mathrm{Ar}}_2$ dication, the NCMCT process results in notably different kinetic energy releases for the $\mathrm{A}{\mathrm{r}}^{+}+\mathrm{A}{\mathrm{r}}^{+}$ channel. It is due, revealed by theoretical calculations, to the special potential energy curve of the responsible $\mathrm{A}{\mathrm{r}}^{2+}-\mathrm{Ar}$ state that possesses many crossing points and thus nonadiabatically couples with the $\mathrm{A}{\mathrm{r}}^{+}-\mathrm{A}{\mathrm{r}}^{+*}$ states in a wide internuclear distance range. Such an NCMCT process is expected to be a general process occurring in weakly bound systems when highly excited. The present work provides a prime collision system to explore the charge transfer in ion-molecule reactions and also brings insight into cluster dissociation mechanism.

We experimentally investigate the dissociative frustrated triple ionization of ArKr dimers induced by a relative phase-controlled linearly polarized two-color femtosecond laser field. In this process, one of the three ionized electrons is recaptured by the triply ionized ArKr, leading to fragmentation via two distinct Rydberg channels: ($\mathrm{A}{\mathrm{r}}^{+*}$, $\mathrm{K}{\mathrm{r}}^{+}$) and ($\mathrm{A}{\mathrm{r}}^{+}$, $\mathrm{K}{\mathrm{r}}^{+*}$). Coincidence measurements are performed for the resulting fragments. By examining the sum momentum of the two fragments along the symmetry axis of the spectrometer in relation to their total kinetic energy release, we establish a method for selectively identifying events corresponding to each Rydberg channel from the raw data. Furthermore, we demonstrate that the emission directions of the Rydberg fragments in the ($\mathrm{A}{\mathrm{r}}^{+*}$, $\mathrm{K}{\mathrm{r}}^{+}$) and ($\mathrm{A}{\mathrm{r}}^{+}$, $\mathrm{K}{\mathrm{r}}^{+*}$) channels can be manipulated by adjusting the relative phase of the two-color laser fields. Notably, these two channels exhibit distinct behaviors in the relative phase-dependent asymmetry as a function of the kinetic energy release of the fragments. Based on the observed asymmetry patterns and the enhanced ionization mechanism, we elucidate the pathways leading to the formation of the ($\mathrm{A}{\mathrm{r}}^{+*}$, $\mathrm{K}{\mathrm{r}}^{+}$) and ($\mathrm{A}{\mathrm{r}}^{+}$, $\mathrm{K}{\mathrm{r}}^{+*}$). Our findings provide an experimental approach and deeper insight into molecular dissociative frustrated ionization in femtosecond laser fields.

Cumulant mapping has recently been suggested [Frasinski, Phys. Chem. Chem. Phys. 24, 20776 (2022)] as an efficient approach to observing multiparticle fragmentation pathways while bypassing the restrictions of the usual coincidence-measurement approach. We present a formal analysis of the cumulant-mapping technique in the presence of moderate external noise, which induces spurious correlations between the fragments. Suppression of a false-cumulant signal may impose severe restrictions on the stability of the experimental setup and/or the permissible average event rate, which increase with cumulant order. We demonstrate that cumulant mapping in an imperfect apparatus remains competitive for dominant processes and for pathways with a background-free marker fragment. We further show that the false-cumulant contributions increase faster than linearly with the average event rate, providing a simple test for the experimental data analysis.

We study the nonequilibrium dynamics of bosons in a two-dimensional optical lattice after a sudden quench from the superfluid phase to the free-boson regime. The initial superfluid state is described approximately using both the Bogoliubov theory and the Gaussian variational principle. The subsequent time evolution remains Gaussian, and we compare the results from each approximation of the initial state by examining different aspects of the dynamics. First, we analyze the entanglement entropy and observe that, in both cases, it increases linearly with time before reaching a saturation point. This behavior is attributed to the propagation of entangled pairs of quantum depletions in the superfluid state. Next, we explore the fate of particle-number symmetry, which is spontaneously broken in the superfluid phase. To do so, we use the entanglement asymmetry, a recently introduced observable that enables us to track symmetry breaking within a subsystem. We observe that its evolution varies qualitatively depending on the theory used to describe the initial state. However, in both cases, the symmetry remains broken and is never restored in the stationary state. Finally, we assess the time it takes to reach the stationary state by evaluating the quantum fidelity between the stationary reduced density matrix and the time-evolved one. Interestingly, within the Gaussian variational principle, we find that an initial state further from the stationary state can relax more quickly than one closer to it, indicating the presence of the recently discovered quantum Mpemba effect. We derive the microscopic conditions necessary for this effect to occur and demonstrate that these conditions are never met in the Bogoliubov theory.

We have determined the atomic mass of ${}^3\mathrm{He}$ to 12 parts per trillion relative precision from a measurement of the cyclotron frequency ratio of ${}^3\mathrm{He}^{+}$ and ${}^{12}\mathrm{C}^{4+}$ in a Penning trap. From the obtained mass of the ${}^3\mathrm{He}^{+}$ ion, the mass of the neutral atom can be calculated without loss of precision: $m\left({}^3\mathrm{He}\right)=3.016029322011\left(35\right)$ u. This result provides independent, high-precision data for the last missing link between the masses in the regime of light ions, thereby resolving discrepancies in the reported masses of light atomic nuclei from various experiments.

Gaussian boson sampling is a popular method for experimental demonstrations of quantum advantage, but many subtleties remain in fully understanding its theoretical underpinnings. An important component in the theoretical arguments for approximate average-case hardness of sampling is anticoncentration, which is a second-moment property of the output probabilities. In Gaussian boson sampling these are given by hafnians of generalized circular orthogonal ensemble matrices. In a companion work by Ehrenberg et al. [Phys. Rev. Lett. 134, 140601 (2025)], we develop a graph-theoretic method to study these moments and use it to identify a transition in anticoncentration. In this work, we find a recursive expression for the second moment using these graph-theoretic techniques. While we have not been able to solve this recursion by hand, we are able to solve it numerically exactly, which we do up to Fock sector $2n=80$. We further derive analytical results about the second moment. These results allow us to pinpoint the transition in anticoncentration and furthermore yield the expected linear cross-entropy benchmarking score for an ideal (error-free) device.

Trapped ions are among the most advanced platforms for quantum simulation and computation. Their capabilities can be further augmented by making use of electronically highly excited Rydberg states, which enable the realization of long-range electric dipolar interactions. Most experimental and theoretical studies so far have focused on the excitation of ionic Rydberg states in linear Paul traps, which generate confinement by a combination of static and oscillating electric fields. These two fields need to be carefully aligned to minimize so-called micromotion, caused by the time-dependent electric field. The purpose of this work is to systematically understand the qualitative impact of micromotion on the Rydberg excitation spectrum, when the symmetry axes of the two electric fields do not coincide. Considering this scenario not only is important in the case of possible field misalignment but becomes inevitable for Rydberg excitations in two- and three-dimensional ion crystals, we develop a minimal model describing a single trapped Rydberg ion, which we solve numerically via Floquet theory and analytically using a perturbative approach. We calculate the excitation spectra and analyze in which parameter regimes addressable and energetically isolated Rydberg lines persist, which are important requirements for conducting coherent manipulations.

Squeezed states of light are one of the most important fundamental resources for quantum optics, optical quantum information processing, and quantum sensing. Recently, it has been experimentally demonstrated that the squeezing of single-mode squeezed vacuum states can be enhanced by probabilistic two-photon subtraction. A further enhancement of the squeezing is subsequently possible by heralded Gaussification, which distills a Gaussian state from the de-Gaussified two-photon subtracted state. Here we provide an extended theoretical analysis of squeezing distillation and purification. We consider a more general scheme in which photon subtraction is combined with a weak coherent displacement. This more flexible scheme allows us to enhance squeezing for an arbitrary input squeezing value. Moreover, if the modified two-photon subtraction operation is properly chosen, then arbitrary strong squeezing can be distilled by subsequent Gaussification. We go beyond pure states and show that the combination of photon subtraction and heralded Gaussification cannot suppress losses that have affected the input state. To overcome this limitation, we propose an alternative de-Gaussifying operation based on a Fock-state filter that removes the single-photon state. With this de-Gaussifying operation and subsequent re-Gaussification, pure single-mode squeezed states can be distilled from a large class of mixed input states. Interestingly, we have found that squeezing distillation by two-photon subtraction is closely related to certain methods for generating Gottesman-Kitaev-Preskill states, which are crucial for optical quantum computing.

We investigate a mode-locking regime in the singly resonant optical parametric oscillator (OPO) employing simultaneous amplitude and frequency modulation of the intracavity field. This OPO exhibits deterministic, “turn-key” formation of a stable, broadband, chirped frequency comb with high conversion efficiency. Comb-forming dynamics follow a simple phase-space dynamical model, governed by cavity dispersion and modulator chirp, which agrees closely with full numerical simulations. The comb exhibits fast, mode-hop-free tuning over the full gain window of the optical parametric amplification crystal, controlled by the modulator frequency. Conditions for comb stability, and techniques to enhance comb bandwidth through intentional phase mismatch and chirping, are investigated.

Levitated optomechanical systems are rapidly becoming leading tools for precision sensing of forces and accelerations acting on particles in the femtogram to nanogram mass range. These systems enable a high level of control over the sensor's center-of-mass motion, rotational degrees of freedom, and electric charge state. For many sensing applications, extending these techniques to arrays of sensors enables rejection of correlated noise sources and increases sensitivity to interactions that may be too rare or weak to detect with a single particle. Here we present techniques capable of trapping defect-free, two-dimensional arrays of more than 25 microspheres in vacuum. These techniques provide independent control of the optical potential for each sphere. Simultaneous imaging of the motion of all spheres in the array is demonstrated using camera-based imaging, with optimized object tracking algorithms reaching a displacement sensitivity below 1 nm/$\sqrt{\mathrm{Hz}}$. Such arrays of levitated microspheres may find applications ranging from inertial sensing to searches for weakly interacting particles such as dark matter.