We propose an analog quantum simulation of chiral magnetic dynamics using ultracold atoms in an optical superlattice. The massive Schwinger model in the zero gauge coupling limit maps onto the Rice-Mele model, with the fermion mass and topological angle encoded in the superlattice parameters. We study the real-time dynamics of the vector current following two quench protocols that drive continuous chirality injection and chirality relaxation. Simulations with realistic superlattice parameters and experimental noise demonstrate clear mass dependence of the current dynamics in both protocols, robust against experimental imperfections. The vector current may be directly measurable via single-bond-resolved detection, establishing cold atom superlattices as a viable platform for probing nonequilibrium chiral phenomena.

Perfect chiral circulation, the sequential transfer of a quantum state around a closed loop with unit fidelity, has been achieved in specific few-site systems, yet the universal physical conditions underlying this phenomenon remain unclear. We prove that discrete translational invariance and an equidistant energy spectrum together constitute the necessary and sufficient conditions for perfect chiral circulation. With this criterion established, an exact closed-form Hamiltonian valid for arbitrary $N$-site rings naturally follows. In the minimal three-site ring, we demonstrate two physically distinct realizations: Floquet engineering of a driven open chain that restores translational invariance by equalizing the couplings and correlated doublon dynamics in an anyon-Hubbard model where fractional statistics intrinsically provide the synthetic flux that renders the spectrum equidistant. Our results establish unified physical criteria for perfect chiral circulation, with potential applications in diverse platforms such as superconducting circuits, cold atoms, classical electrical circuits, and photonic synthetic dimensions, and further extend this framework beyond spatial transport by incorporating internal degrees of freedom such as spin.

Thermal management in coupled quantum systems is essential, given the inherent fragility of quantum states and correlations. In this work, we theoretically investigate thermal reconfiguration by manipulating the steady-state phonon currents and phonon numbers in an optomechanical array. The system consists of $N$ cells, each containing an optical cavity coupled to a mechanical resonator. Each resonator is coupled to an independent thermal bath, its temperature increasing with the site index. This setup creates a temperature gradient that induces a steady-state phonon current flowing from the hotter region to the colder region of the array. The direction of the phonon current can be manipulated by introducing a synthetic gauge field, which is achieved by modulating the driving laser with a site-dependent phase. This modulation results in a phase-dependent linearized optomechanical coupling. Counterintuitively, the direction of the phonon current can be reversed to flow against the temperature gradient by tuning the synthetic phase. When the direction is reversed, the total steady-state phonon number is further reduced. This indicates that thermal reconfiguration can be realized via the introduction of a synthetic phase. Our results provide a phase-controlled mechanism with potential applications in thermal management for quantum information processing.

We consider the combined effect of a Duffing nonlinearity and the optomechanical interaction on the cavity density of states (DOS), which is directly observable in optomechanically induced transparency (OMIT) experiments. Both nonlinearities introduce the same type of interaction between polaritons, producing a distinct feature in the optical response. We derive the resonant condition that enhances the nonlinear scattering between polaritons and study the parameter dependence of the cavity DOS in detail. This allows us to characterize the typical strength and optimal conditions for observing the quantum effects of the Duffing nonlinearity in OMIT experiments.

A system, comprising a qubit pair coupled to a common cavity, is studied with the aim of establishing qubit entanglement. This study is a continuation of an earlier publication [Phys. Rev. A 111, 043705 (2025)], where a similar model was investigated for an initially vacuum cavity. In the present paper, a cavity with a finite initial occupancy is considered and the effect of asymmetric qubit-cavity couplings is investigated. For a closed system scenario, the ratio of the qubit-cavity couplings shows a minimum value below which no maximally entangled qubit state is available. The threshold value is shown to depend critically on the initial number of photons present in the cavity. It is shown that a greater photon number prefers symmetric couplings for generating maximal entanglement. For a driven-dissipative case steady-state entanglement is shown to depend nonmonotonically on the qubit drive. For a moderate drive, steady-state entanglement decreases with decreasing coupling symmetry, leading to a regime of “no entanglement.” Interestingly, as the symmetry is further decreased, steady-state entanglement again becomes finite. The Intricate interplay of drive, dissipation, and coupling asymmetry is shown to be pivotal for steady-state entanglement generation.

We study two distinct diagnostics of bipartite quantum channels: the average fidelity between a desired state and noisy output across different classes of input states, and generation of entanglement from pure product input states, quantified by well-defined entangling power. These diagnostics are generally independent, but together they provide a more complete description of bipartite channels. We show that the fidelity averaged over any local-unitary orbit with fixed Schmidt coefficients for equal local dimensions is completely determined by the average input-output fidelity and its restriction to product inputs. We also introduce concurrence- and negativity-based entangling power for two-qubit channels, prove their convexity and monotonicity under local postprocessing, and show that, unlike the previously proposed linear-entropy quantity, they vanish for all separable channels. Representative separable and nonseparable channels are investigated. Finally, we generalize our definitions of entangling power to nonproduct inputs, and provide an analytical lower bound for the concurrence-based entanglement variation, showing its effectiveness with specific examples.

We present a protocol using neural networks to simultaneously optimize the quantum error-correcting code space and the corresponding recovery map in the framework of continuous-time quantum error correction. Given a Hilbert space and a noise process—potentially correlated across both space and time—the protocol identifies the optimal recovery strategy, measured by the average logical state fidelity. This approach enables the discovery of recovery schemes tailored to arbitrary device-level noise.

Quantum imaginarity is a distinct resource in quantum information theory, yet its nonlocal properties have not been fully explored. Here, we report an experimental study of the nonlocal advantage of quantum imaginarity (NAQI), in which local measurements on one subsystem can steer the average imaginarity of the conditional states of the other subsystem beyond the corresponding classical bound. The $l_1$-norm of imaginarity inequality is adopted as an experimentally accessible witness. A hybrid optimization algorithm that combines a genetic algorithm with sequential quadratic programming is developed to avoid local optima and accelerate the search for optimal measurement settings. Using polarization-encoded photonic qubits, we prepare two classes of two-qubit Bell-diagonal states and experimentally characterize the imaginarity of the conditional states following local measurements. Clear violations of the $l_1$-norm of imaginarity inequality are observed, providing an experimental certification of NAQI. We further investigate the relationship among NAQI, the nonlocal advantage of quantum coherence (NAQC), and Bell nonlocality (BN) based on their respective inequality criteria. For the two-qubit Werner states considered in this work, the regions of states that violate the respective criteria satisfy ${\mathcal{D}}_{\mathrm{NAQC}}\subset {\mathcal{D}}_{\mathrm{NAQI}}\subset {\mathcal{D}}_{\mathrm{BN}}$. Our work provides an experimental realization of NAQI and a comparison of different forms of quantum nonclassicality in a photonic platform.

In this work we propose a quantum-walk model, named controlled intermittent quantum walks (CIQWs), where one performs a continuous quantum walk for a period of time under a certain control signal and then adjusts the control signal and performs a continuous quantum walk for another period of time under the new control signal, repeating the operation in this way. We apply the model to tackle the fundamental problem of finding an unknown marked vertex on a graph, known as spatial search, obtaining a universal quantum search algorithm. For any graph with any number of marked vertices, our CIQW-based algorithm achieves a quadratic speedup in query complexity over classical random-walk-based algorithms. Compared to state-of-the-art results in quantum spatial search, our algorithm achieves significantly lower query complexity in certain cases. Furthermore, by using the simpler Laplacian matrix as the Hamiltonian for our continuous-time quantum walk, we facilitate a more concrete and concise search algorithm. These features distinguish our work and add a fresh perspective to the growing body of quantum spatial search algorithms.

Discriminating between noisy quantum processes is a central primitive for quantum communication, metrology, and computing. While discrimination limits for finite-dimensional channels are well understood, the continuous-variable setting—particularly under experimentally relevant energy constraints—remains significantly less developed. In this work, we establish an energy-constrained chain rule for the Belavkin-Staszewski channel divergence, which yields a fundamental upper bound on the error exponents achievable by fully adaptive, energy-constrained quantum channel discrimination protocols. We then derive efficiently computable bounds on asymmetric error exponents for energy-constrained discrimination of bosonic dephasing and loss-dephasing channels. Specifically, we show that three operationally relevant quantities—the measured relative entropy, the Umegaki relative entropy, and the geometric Rényi divergence—admit semidefinite program (SDP) formulations when the input energy is bounded and the Hilbert space is suitably truncated. Applying these tools, we demonstrate that optimal probes for these channels under energy constraints are Fock diagonal, and we also enable numerically precise evaluation of bounds on achievable error exponents across discrimination strategies ranging from separable to fully adaptive. The resulting SDPs provide practical benchmarks for quantum-limited sensing in low-energy bosonic platforms.

Modern precision measurements, such as interferometry for detecting gravitational waves, rely on the estimation of optical phases encoded in light fields. Here we propose to exploit the collectively enhanced output field of a driven-dissipative many-body quantum system as a light source in order to improve the precision of estimating optical phases. Pronounced temporal correlations of such output fields benefit the sensitivity of measurement protocols, which we show theoretically by employing a boundary time crystal as a light source. The fundamental bound on the precision of such estimation shows scaling with the number of constituents $N$ of the many-body system as $N^4$ while scaling linearly with the measurement time $T$. We discuss this scaling from the perspective of both the resources employed to build the light source and the resources produced by the light source. We show that a measurement scheme, in which the phase-shifted light field is guided into an auxiliary replica system, which serves as a detector that is sensitive to nontrivial temporal correlations of light, can saturate the fundamental bound on precision at an optimal operating point.

We present an in-depth study of the Dicke quantum battery introduced in Phys. Rev. Lett. 134, 130401 (2025), in particular, showing explicitly that the $N^2$ power charging advantage found in the extensive regime agrees with the quantum speed limits for open systems dynamics. We also study the coherent energy extraction by an external driving field, thus extending previous results of Monsel et al. [Phys. Rev. Lett. 124, 130601 (2020)] to an $N$-atom “charger.”

Recent advances in strong x-ray laser techniques enable the study of nonlinear multiphoton ionization in extreme high-frequency fields. Although the stabilization regime in such fields is theoretically established, its modified properties in the nondipole regime for long laser pulses remains unknown. Here we numerically investigate the strong-field ionization of hydrogen or a hydrogenlike ion in a long XUV laser pulse in the nondipole regime. Our study of the time-dependent quantum dynamics reveals a quasiperiodic modulation of the ionization yield as a function of pulse duration. We demonstrate that the Coulomb-field-induced slow oscillation of the ionized electron wave packet during the interaction is responsible for the observed modulation of the ionization yield. Furthermore, we scrutinize the unusual photon momentum sharing between the photoelectron and the ion in this extreme regime. These effects are observable in upcoming x-ray free-electron laser facilities.

Measurement plays a crucial role in a quantum system beyond just learning about the system state: it changes the postmeasurement state and hence influences the subsequent time evolution; further, measurement can even create entanglement in the postmeasurement conditional state. In this work, we study how a careful choice of parameters for a typical measurement process on cold atom systems—phase-contrast imaging—strongly impacts both what the experimentalist observes and the measurement backaction on the system, including the creation and diffusion of quasiparticles emerging from the quantum many-body dynamics. We focus on a Bose-Einstein-condensate array in the low-temperature, low-momentum limit. Our theoretical investigation identifies regimes in which the imaging light probes either bare atomic or Bogoliubov quasiparticle dynamics. Furthermore, we show that, together with a weak global drive, appropriate tuning of the measurement bandwidth enables direct probing of Bogoliubov quasiparticles while controlling the measurement-induced creation and diffusion of quasiparticles across momentum modes. These results clarify how the measurement protocol determines both the observed excitations and the corresponding measurement backaction in weakly interacting Bose-Einstein condensates.

We report on an imaging scheme for quantum gases that enables simultaneous detection of two spin states with single-atom resolution. It utilizes the polarization of the emitted photons during fluorescence by choosing appropriate internal states of lithium-6 atoms in a magnetic field. This scheme can readily be implemented to obtain in situ spin correlations in a wide variety of experimental settings.

The dyadic Green’s function is an important tool of computational photonics, giving deeper insights into light-matter interaction. We present an operator approach to the derivation of the dyadic Green’s function of a generic anisotropic planarly layered medium for both electric and magnetic fields. The resulting Green’s function is expressed through the evolution operators (a kind of transfer matrices) of the comprising layers and the surface impedance tensors, the singular term being naturally separated from other terms. The operator approach to the Green’s function simplifies both the conceptual understanding of the problem and the subsequent practical applications, some of which are demonstrated here. The proposed approach can be easily generalized to the case of spherical and cylindrical layers, as well as bi-anisotropic layered media. The obtained results can be applied in nanophotonics engineering problems.

Resonances associated with complex-frequency poles are ubiquitous across physics and can arise in any open system, ranging from subwavelength particles and cavities to biological structures. When two such resonances coalesce, they form exceptional points (EPs), non-Hermitian singularities known to produce unusual spectral and dynamical behavior. However, the dynamics of the response of such resonances and exceptional points to a complex-frequency drive has remained largely unexplored. Here, we experimentally observe the temporal response of complex-frequency resonances and theoretically study it for exceptional points, demonstrating that the passive system's initial response for a decaying drive grows linearly, with enhanced growth at EPs. Closed-form theory for general resonators, extended to higher-order modes, predicts efficient power transfer with $t$ and $t^2$ scaling for complex single poles and EPs, respectively, at all times. We analyze these effects in subwavelength optical scatterers and experimentally in an electrical circuit analogue, with excellent agreement, and explore configurations that capture EP-enhanced growth.

We investigate the bipartite and tripartite entanglement and the mechanical ground-state cooling in a hybrid microwave-optomechanical circuit. This system, which consists of a common microwave $LC$ resonator, two single-Cooper-pair transistors (SCPTs), and two micromechanical resonators, when driven in a specific regime, behaves equivalently as an optomechanical system with a single cavity field interacting with two mechanical resonators. The cavity couples to the mechanical modes via radiation-pressure, cross-Kerr (CK) type nonlinearities, and an interaction between the two mechanical resonators. First, we demonstrate that adjusting the gate-charge deviation and the detuning frequency enables manipulation of multipartite entanglement within this system. Then, our results indicate that distinct types of CK couplings enhance either the cooling efficiency or the entanglement generation. More specifically, the three-mode CK coupling contributes to multipartite entanglement, whereas the conventional CK coupling plays a key role in simultaneous ground-state cooling of the mechanical modes. This observed competition between cooling efficacy and entanglement formation yields insights for the optimal design of hybrid quantum systems built for multitask operations.