Continuous-wave (cw) architectures provide a promising route to interface disparate quantum systems by relaxing the need for precise synchronization. While essential cw components, including microwave single-photon transistors and microwave–optical converters, have been explored, an all-optical cw single-photon transistor has remained a missing piece. We propose a high-efficiency, high-gain implementation using Rydberg atoms, in which a control photon disrupts the transmission of a continuous probe beam via the van der Waals interaction. This device completes the set of components required for cw processing of quantum signals and paves the way for all-optical processing at the quantum level.

The trapping and cooling of photon gases in microcavities has been used to create Bose-Einstein condensates. We investigate the conditions required for condensation in dye-filled microcavities, with photon populations created either by driving a transition of the dye, or by coupling the cavity modes to a thermal photon reservoir such as sunlight. We find that the threshold pump temperature, above which condensation appears, is determined by the second law of thermodynamics. The minimum achievable threshold is that of a reversible three-level heat engine, which we show arises in the dye-pumped case, and for pumping of the modes of a two-level cavity. For a many-level cavity condensation occurs at a similar but higher temperature. Our results show that photon condensates can be produced by pumping with incoherent thermal sources, opening possibilities for coherent light generation, energy harvesting, and experimental studies of quantum heat engines.

The Fraunhofer diffraction of quantum particles from materials with sharp electron-density edges or symmetric bond structures is ubiquitous. In contrast, diffraction from atoms with a characteristic asymptotically diffused electron distribution is far less intuitive, although known for many years. The current study unravels an unusual diffraction mechanism of elastic electrons from diffused atomic diffractors. Consequently, the fringe pattern converted to the Fourier reciprocal space maps out the effective scattering potential, which is not accessible in direct measurements. This may benefit large-volume and multiscale computational modeling of processes in materials where adopting the complex exact potentials is challenging and expensive. The study employs a relativistic partial-wave analysis with atoms modeled in the Dirac-Fock formalism and performs $e$-Cd measurements in absolute scale. Analysis for Mg, Ba, and Ra targets demonstrates the universality of the mechanism.

Recent experiments demonstrate that rapidly rotating Bose-Einstein condensates (BECs) near the lowest Landau level can self-organize into interaction-driven persistent quantum Hall droplet arrays. Inspired by this discovery, we investigate the formation and dynamics of single quantum Hall droplet and droplet arrays in rapidly rotating BECs. Guided by a rigorous theorem on localized many-body states for two-dimensional interacting systems in a magnetic field, we construct single quantum Hall droplet and droplet array states which are shown to be stationary solutions to the Gross-Pitaevskii equation in the rotating frame. The single quantum Hall droplet is shown to be dynamically stable, which underpins its role as the basic unit in a droplet array. The stability of the quantum Hall droplet arrays is demonstrated by their dynamic formation from a phase engineered initial condensate. Our study sheds light onto the nature of the quantum Hall droplet state in a rapidly rotating BEC and offers a new approach for generating and manipulating quantum Hall droplet arrays through designing the initial condensate phase.

Periodic driving of particles can create crystalline structures in their dynamics. Such systems can be used to study solid-state physics phenomena in the time domain. In addition, it is possible to realize photonic time crystals and to engineer the wave-number band structure of optical devices by periodic temporal modulation of the properties of light-propagating media. Here, we introduce a versatile approach which uses traveling-wave resonators to emulate various condensed matter phases in the time dimension. This is achieved by utilizing temporal modulation of the permittivity and the shape of small segments of the resonators. The required frequency and depth of the modulation are experimentally achievable which opens a pathway for the practical realization of crystalline structures in time in microwave and in optical systems.

We study the classical dynamics of a Paul-trapped ion in a low-density bath of atoms above $1\mu \mathrm{K}$. We find that lower-energy collisions with more massive atoms, especially at energies less than the initial micromotion heating, are more likely to form atom-ion complexes. These complexes evolve in a fractal structure for every scattering observable, showing nonhyperbolic chaotic dynamics. To explore the chaotic dynamics, we use a GPU-accelerated methodology allowing us to run over $3\times {10}^8$ trajectories of a ${}^{174}\mathrm{Yb}^{+}$ and different atoms. As a result, after analyzing the dynamics as a function of the atom species, collision energy, trap parameters, and ion-atom potential depth, we find a link between heating and the onset of chaos in the first atom-ion interaction that occurs when a low-density atomic bath is merged with a trapped ion.

We investigate the chiral dynamics of locally interacting bosons in a two-leg flux ladder, where on-site interactions, despite being fully isotropic, counterintuitively reverse the flux-induced chiral transport of density distribution. For a Bose-Einstein condensate (in the mean-field regime), this reversal arises from an interaction-driven dynamical band-occupation inversion, which selectively populates single-particle states of the opposing chirality. Strikingly, the chiral-transport inversion has a few-body, hence beyond-mean-field, origin, as the formation of two-body bound states with reversed chirality dominates the few-body dynamics. This dual pathway, that is, occupation inversion and bound-state formation, underlies the chiral-transport inversion, which challenges the conventional wisdom that isotropic interactions cannot bias density transport. Our work reveals the interplay between interactions and chirality and highlights how correlations engineer exotic quantum transport.

We demonstrate that dissipative state preparation protocols in many-body systems can be substantially accelerated via the quantum Mpemba effect. Our approach exploits weak symmetries to analytically identify a class of simple, experimentally realizable states that converge exponentially faster to the steady state than typical random initializations. In particular, we study the preparation of a lattice Bose-Einstein condensate (BEC), where the depletion can be controlled via the dissipation strength. We also show how to tune the momentum of the created high-fidelity BEC by combining superfluid immersion with lattice shaking. Our theoretical predictions are confirmed by numerical simulations of the dissipative dynamics. This protocol paves the way to unlock the enormous potential of the dissipative preparation of highly entangled states in analog quantum simulators.

A shell-shaped Bose-Einstein condensate released from its confinement expands radially both outward and inward, displaying a self-interference pattern characterized by a density peak surrounded by a halo. Here we analyze how an external imprinting or the thermal fluctuations of the condensate phase influence this expansion. In both cases we find that the curved geometry filters the imploding finite angular-momentum modes via a radial centrifugal potential, so that only the condensate state can reach the origin and form the central peak. As a consequence, we observe a pronounced dependence of the central density on the imprinting strength and on temperature. This geometric filtering effect characterizes the free expansion of curved atomic gases in contrast with flat counterparts, it is easily observable in the available experimental platforms and enables two-dimensional shells thermometry via simple absorption-imaging techniques.

A Hamiltonian with eigenenergy $E_n={\rho }_n(1-{\rho }_n)$ has been constructed, where ${\rho }_n$ denotes the $n\mathrm{th}$ nontrivial zero of the Riemann zeta function. To construct such a Hamiltonian, we generalize the Berry-Keating paradigm and encode number-theoretic information into the Hamiltonian using modular forms. Although our construction does not resolve the Hilbert-Pólya conjecture (since the eigenstates corresponding to $E_n$ are not normalizable), it provides a novel physical perspective on the Riemann Hypothesis (RH). In particular, we propose a physical interpretation of RH, which could offer a potential pathway toward its proof.

With an all-optical technique, we demonstrate the experimental feasibility to create a molecular ensemble with higher degrees of orientation ($|\langle cos{\theta }_{\text{2D}}\rangle |>0.23$) in a field-free space. In order to achieve higher degrees of orientation, two-color laser pulses with longer durations of $\sim 10\mathrm{ns}$ and carbonyl sulfide (OCS) molecules in the rotational ground state, which are selected by a molecular deflector, are employed. To prepare an oriented ensemble of OCS molecules in a field-free space, the 10-ns two-color pulses are rapidly turned off with a plasma shutter technique, in which the relative phase between the two wavelengths is stabilized with a feedback technique. The molecular orientation dynamics after the rapid turnoff of the two-color pulses is observed and well reproduced by numerical simulations.

We demonstrate a frequency-domain echo atom interferometer for measurements of gravitational acceleration $g$. The experiment relies on a sample of laser-cooled atoms at a temperature of approximately $10\mu \mathrm{K}$. Two composite running wave pulses with a relative detuning $\delta$, which are separated by a time $T$, are used to excite the sample and observe a grating echo at time $t=2T$. The echo is detected by coherently backscattering a traveling-wave readout pulse from the optical lattice that forms in the temporal vicinity of the echo time. The phase of the backscattered signal exhibits a linear dependence on $\delta$ for a fixed value of $T$ and the offset of this linear trend can be used to infer the value of $g$.

We investigate the laboratory-frame angular emission distribution of photoelectrons, ejected by circularly polarized light from chiral molecules, theoretically beyond the electric-dipole approximation. We demonstrate that the helicity-dependent forward-backward asymmetry, which is governed by the electric-dipole interaction and known as photoelectron circular dichroism (PECD), can be altered significantly by the helicity-independent asymmetry, which is induced by nondipole contributions. Our findings are exemplified by numerical calculations on the inner-shell photoionization of the bromine atom in the epibromohydrin molecule. The uncovered effect is expected to be omnipresent in the deep inner-shell ionization and needs to be taken into consideration in the interpretation of experiments on PECD in chiral molecules.

We present a novel method for mapping in situ the spatial distribution of photon momentum across a laser beam using a Bose-Einstein condensate (BEC) as a moving probe. By displacing the BEC, we measure the photon recoil by atom interferometry at different positions in the laser beam and thus reconstruct a two-dimensional map of the local intensity and effective dispersion of the $\vec{k}$ wave vector. Applied to a beam diffracted by a diaphragm, this method reveals a local extra recoil effect, which exceeds the magnitude $h\nu /c$ of the individual plane waves over which the beam can be decomposed. This method offers a new way to precisely characterize wavefront distortions and to evaluate one of the major systematic bias sources in quantum sensors based on atom interferometry.

Optical transitions in highly charged ions can be very sensitive to hypothetical beyond-the-standard-model phenomena. Those near the degeneracy due to the $5s\text{−}4f$ level crossing are especially promising. We present measurements of ${\mathrm{Os}}^{15,16,17+}$ ions at an electron beam ion trap and corresponding predictions of several transitions that show a high sensitivity to hypothetical fifth forces and possible violations of local Lorentz invariance. We found electric quadrupole transitions in ${\mathrm{Os}}^{16+}$, which are suitable for frequency metrology due to linewidths down to $44\mu \mathrm{Hz}$. Our calculations show the need for including enough inner-shell excitations to avoid an overestimation of interconfiguration transition rates, which were too faint for detection at the present signal-to-noise ratio.

Nonlinear Compton scattering holds great promise for creating powerful narrow-band sources of high-energy radiation. However, a spectral broadening of the harmonics arises for laser pulses with a realistic envelope due to inhomogeneous light pressure, reducing the source brightness. To effectively use the nonlinear Compton scattering, a rectangular laser pulse shape is more favorable. In this Letter, a pulse-stacking method is studied to obtain a close-to-rectangular envelope and a narrow-band Compton source in the nonlinear regime. The impact of stacking errors in amplitude, phase, and delay on the source brightness is investigated. A method is presented to obtain a multicolor gamma source.

In the realm of quantum information processing, the efficient characterization of entangled states poses an overwhelming challenge, rendering the traditional methods including quantum tomography unfeasible and impractical. To tackle this problem, we propose a new verification scheme using collective strategies, showcasing arbitrarily high efficiency that beats the optimal verification with global measurements. Our collective scheme can be implemented in various experimental platforms and scalable for large systems with a linear scaling on hardware requirement, and distributed operations are allowed. Notably, larger ensembles can always improve the efficiency further, but without increasing the quantum memory. More importantly, the approach consumes only a few copies of the entangled states, while ensuring the preservation of unmeasured ones, and even boosting their fidelity for any subsequent tasks. Furthermore, our protocol provides additional insight into the specific types of noise affecting the system, thereby facilitating potential targeted improvements. These advancements hold promise for a wide range of applications, offering a pathway towards more robust and efficient quantum information processing.

We investigate the photon statistics of an ensemble of coherently driven noninteracting two-level atoms in the weak driving regime. As it turns out, the system displays unique emission characteristics that are strongly in contrast to the emission of classical oscillating dipoles. By deriving the second-order autocorrelation function, we show that extraordinary two-photon correlations are obtained, ranging from strong antibunching to superbunching. These features are enhanced by disorder in the emitter positions, and the control parameter is the number of excitations in the system. We observe the appearance of bunching and antibunching when the light is scattered by the atoms predominantly coherently, i.e., mimicking classical Rayleigh scattering, whereas thermal photon statistics is obtained when the light is scattered via spontaneous decay, a well-known quantum effect. The underlying mechanism is the interplay between coherent scattering, which exhibits spatial fluctuations due to interference, and dissipation in the form of isotropic spontaneous decay.

We explore the task of learning about the dynamics of a Markovian open quantum system by monitoring the information it radiates into its environment. For an open system with Hilbert space dimension $D$, the quantum state of the emitted radiation can be described as a temporally ordered matrix-product state. We provide simple analytical expressions for the quantum Fisher information (QFI) of the radiation state, which asymptotically scales linearly with the sensing time unless the open system has multiple steady states. We characterize the crossovers in QFI near dynamical phase transitions, emphasizing the role of temporal correlations in setting the asymptotic rate at which QFI increases. We identify conditions under which information encoded in the mixed radiation state can be reliably accessed over both short and long timescales. We discuss when optimal sensing is possible with instantaneously measured radiation.

We introduce a systematic framework to derive the effective Hamiltonian governing the coherent dynamics of non-Markovian open quantum systems. By applying the minimal dissipation principle, we uniquely isolate the coherent contribution to the time-local generator of the reduced dynamics. We derive a general expression for the effective Hamiltonian and develop a recursive perturbative expansion that expresses it in terms of system-bath interaction terms and bath correlation functions. This expansion provides a systematic tool for analyzing energy renormalization effects across different coupling regimes. Applying our framework to paradigmatic spin systems, we reveal how environmental correlations influence energy shifts and eigenbasis rotations, offering insights into strong-coupling effects and non-Markovian quantum thermodynamics.