We study the combination of the discrete Talbot effect with Bloch-Zener oscillations in binary waveguide arrays (BWAs) under the influence of an external linear potential when the input beam with transverse period $N=2$ is launched into the system. We show that when the Dirac mass $\sigma$ is small enough, the light carpets in BWAs are almost perfectly periodic in both the transverse and longitudinal directions. In this case, light carpets have a longitudinal period equal to the Bloch-Zener oscillation period $z_B$. The discrete Talbot effect in BWAs under the influence of the external potential can be used to switch between various kinds of the light beam distribution at the output of the system with many channels at the same time just by tuning the external potential parameter $\alpha$. In particular, these optical switches operate in the low-power regime because they do not require any nonlinear effects.

We propose high-fidelity single-qubit spin-dependent kicks (SDKs) for trapped ions using nanosecond Raman pulses via amplitude modulation of a continuous-wave laser with a tunable beat frequency. We develop a general method for maintaining SDK performance in the presence of micromotion by identifying optimal choices of the rf phase and frequency that suppress unwanted backward kicks. The proposed scheme enables SDK infidelities as low as ${10}^{-9}$ in the absence of micromotion, and on the order of ${10}^{-5}$ with micromotion. This study lays the foundation for the realization of sub-trap-period and high-fidelity two-qubit gates based on SDKs.

With the advent of exquisite quantum emulators, storing highly entangled many-body states becomes essential. While entanglement typically builds over time when evolving a quantum system initialized in a product state, freezing that information at any given instant requires quenching to a Hamiltonian with the time-evolved state as an eigenstate, a concept we realize via an emergent Hamiltonian framework. While the emergent Hamiltonian is generically nonlocal and may lack a closed form, we show examples where it is exact and local, thereby enabling, in principle, indefinite state storage limited only by experimental imperfections. Unlike other phenomena, such as many-body localization, our method preserves both local and global properties of the quantum state. In some of our examples, we demonstrate that this protocol can be used to store maximally entangled multiqubit states, such as tensor products of Bell states, or fragile, globally distributed entangled states, in the form of Greenberger-Horne-Zeilinger states, which are often challenging to initialize in actual devices.

Quantum key distribution (QKD) is a crucial solution for future secure communications because it provides information-theoretic security based on the principles of quantum mechanics. However, in practical polarization-encoded QKD systems, due to physical structural limitations, practical modulators inevitably introduce polarization-dependent loss (PDL), which can undermine the security of the generated keys. In this work, we propose and experimentally demonstrate a polarization-encoded measurement-device-independent QKD (MDI-QKD) system based on two silicon-on-insulator (SOI) chips, and explicitly quantify the impact of PDL in key rate estimation. We successfully extend the transmission distance to 202 km, which fully validates the feasibility of the polarization-loss-tolerant method. This work provides essential technical support for the deployment of low-cost, high-security integrated optical quantum networks with imperfect practical devices.

Quantum computing shows promise for addressing computationally intensive problems, but is constrained by the exponential resource requirements of general quantum state tomography (QST), which fully characterizes quantum states through parameter estimation. We introduce the QST with Chebyshev polynomials, an approximate tomography method for pure quantum states encoding complex-valued functions. This method reformulates tomography as the estimation of Chebyshev expansion coefficients, expressed as the inner products between the target quantum state and Chebyshev basis functions, measured using the Hadamard test circuit. By treating the truncation order of the Chebyshev polynomials as a controllable parameter, the method provides a practical balance between efficiency and accuracy. For quantum states' encoding functions dominated by large-scale features, such as those representing fluid flow fields, appropriate truncation enables faithful reconstruction of the dominant components via quantum circuits with linear depth, while keeping both measurement repetitions and postprocessing independent of qubit count, in contrast to the exponential scaling of full measurement-based QST methods. Validation on analytic functions and numerically generated flow-field data demonstrates accurate reconstruction and effective extraction of large-scale features, indicating the method's suitability for systems governed by macroscopic dynamics.

We apply a Bayesian agent-based framework inspired by a Bayesian interpretation of quantum theory (QBism) to iterations of two quantum games, the Clauser-Horne-Shimony-Holt (CHSH) game and the quantum prisoners' dilemma. In each two-player game, players hold beliefs about an amount of shared entanglement and about the actions or beliefs of the other player. Each takes actions which maximize their expected utility and revises their beliefs with the classical Bayes rule between rounds. We simulate iterated play to see if and how players can learn about the presence of shared entanglement and to explore how their performance, their beliefs, and the game's structure interrelate. In the CHSH game, we find that players can learn that entanglement is present and use this to achieve quantum advantage. We find that they can only do so if they also believe the other player will act correctly to exploit the entanglement. In the case of low or zero entanglement in the CHSH game, the players cannot achieve quantum advantage, even in the case where they believe the entanglement is higher than it is. For the prisoners' dilemma, we show that assuming onefold rational players (rational players who believe the other player is also rational) reduces Eisert et al.'s quantum extension of the prisoners' dilemma to a game with only two strategies, one of which (defect) is dominant for low entanglement, and the other (Eisert et al.'s quantum strategy $Q$) is dominant for high entanglement. For intermediate entanglement, neither strategy is dominant. We again show that players can learn entanglement in iterated play. We also show that strong belief in entanglement causes optimal play even in the absence of entanglement, showing that belief in entanglement is acting as a proxy for the players trusting each other. Our work may point to future applications in resource detection and quantum algorithm design.

Quantum masking is a special type of secret sharing in which some information gets reversibly distributed into a multipartite system, leaving the original information inaccessible to each subsystem. This paper proposes a dynamical extension of quantum masking to the level of quantum channels. In channel masking, the identity of a channel becomes locally hidden but still globally accessible after its output is sent through a bipartite broadcasting channel. We first characterize all families of $d$-dimensional unitaries that can be isometrically masked, a condition that holds even in the presence of depolarizing noise. For the case of qubits, we identify which families of Pauli channels can be masked, and we prove that a qubit channel can be masked against the identity if and only if it is unital and has a pure-state fixed point. Masking against the identity describes a scenario in which channel noise becomes completely delocalized through a broadcast map and undetectable through subsystem dynamics alone.

Conventional practice of spatially resolved detection in diffusion-coupled thermal atomic vapors implicitly treats localized responses as mutually independent. However, in this study, it is shown that observable correlations are governed by the intrinsic spatiotemporal covariance of a global spin-fluctuation field, such that spatial separation specifies only overlapping statistical projections rather than independent physical components. A unified field theoretic description is established in which subensembles are defined as measurement-induced statistical projections of a single stochastic field. Within this formulation, subensemble correlations are determined by the covariance operator, inducing a natural geometry in which statistical independence corresponds to orthogonality of the measurement functionals. For collective spin fluctuations described by a diffusion-relaxation Ornstein-Uhlenbeck stochastic field, the covariance spectrum admits only a finite set of fluctuation modes in a bounded domain, imposing an intrinsic, field-level limit on the number of statistically distinguishable subensembles. The loss of subensemble independence is formalized through the notion of spatial sampling overlap, which quantifies the unavoidable statistical coupling arising from shared access to common low-order fluctuation modes. While multichannel atomic magnetometry provides a concrete physical setting in which these constraints become explicit, the framework applies generically to diffusion-coupled stochastic fields.

Direct measurements of the ground-state magnetically insensitive hyperfine transition $|F=2,m_F=0\rangle \to |F=1,m_F=0\rangle$ of ${}^9\mathrm{Be}^{+}$ ions have been performed using microwave-driven state transfer. The ${}^9\mathrm{Be}^{+}$ ions are confined and laser cooled in a linear Paul trap, forming a Coulomb crystal. The transition frequencies have been measured over a magnetic-field range of $\pm 0.5$ mT centered at zero magnetic field and the acquired data were fitted accounting for the high-order Zeeman effect. The hyperfine constant $A$ is determined to be $-625.008840\left(35\right)$ MHz, achieving a relative precision of $5.6\times {10}^{-8}$.

Attosecond streaking camera is an ex situ technique in which a linearly polarized (LP) XUV attopulse produces an electron wavepacket by photoionization in the presence of an IR femtopulse. By moving the two synchronous oppositely circularly polarized XUV pulses (that make the ionizing LP pulse) apart in time, we propose an attosecond double-slit streak camera scheme to see information loss in polarization-dependent two-slit phenomena. Such streaking interferogram is then composed of several Feynman's thought experiments in time domain, in which electrons are affected by the IR pulse as they exit the two attoslits upon XUV ionization processes to form Archimedean spiral patterns. As a first proof-of-principle, when the IR femtofield and first XUV attopulse are synchronous, a loss of contrast through an effective dephasing is seen in the simulated momentum and energy distributions of the photoelectron. It is shown that the contrast between bright and dark interference fringes diminishes predominantly along the IR-field polarization axis and is sensitive to the IR-field waveform. Falling in the regime of linear optics, our predictions are based on solutions of full-dimensional time-dependent Schrödinger equation (TDSE) and analyzed using perturbation theory, strong-field approximation, and TDSE calculations for the populated ionization channels. Our which-time information scheme provides further confirmation of the wave-particle duality.

The dynamics of a two-dimensional Bose-Einstein condensate mixture, loaded into a dual-core trap, when the beyond-mean-field effects are taken into account, are considered. The effects of quantum fluctuations are described by the Lee-Huang-Yang correction terms in the extended coupled Gross-Pitaevskii equations (GPE). The spatially uniform and inhomogeneous condensate cases are studied. In the first case, the parameter regimes associated with macroscopic quantum tunneling, macroscopic self-trapping, and revival-like localization dynamics are found. The Josephson oscillation frequencies for both the zero-phase and the $\pi$-phase modes are derived. As the total atom number is varied, the dynamics exhibit a nontrivial bifurcation structure: along the zero-phase branch, two successive pitchfork bifurcations generate bistability and hysteresis, while the $\pi$-phase branch shows a single pitchfork bifurcation. In the second case, the Josephson dynamics for quantum droplets and vortices are investigated. The analytical predictions for the oscillation frequencies of the atomic population between quantum droplets are found, and results are validated by direct numerical simulations of the system of coupled extended GPE. The existence of the Andreev-Bashkin nondissipative drag through simulations of droplet-droplet interactions is shown. The Josephson dynamics of vortex states are studied. It was found that vortices with topological charge $S$ and sufficiently small particle number are typically unstable, breaking up into $S+1$ (and occasionally $S+2$) fundamental, nonvortical fragments, with the time to breakup increasing as the particle number grows. It is also found that unstable asymmetric vortices exhibit the splitting and/or crescentlike instability. For vortices with sufficiently large norms, long-time simulations confirm robust stability against small perturbations. In this stable regime, the properties of Josephson oscillations and Andreev-Bashkin-type entrainment for vortex states with charges $S=1,2$, and 3 are investigated.

We investigate the mean-field scattering dynamics of a quasi-one-dimensional Bose-Einstein condensate interacting with a Rosen-Morse (RM) potential. For specific potential and nonlinearity parameters, we derive exact degenerate reflectionless states (with twofold or threefold degeneracy). Using the Bogoliubov–de Gennes approach, we analyze the stability of these reflectionless degenerate states, demonstrating that only one solution within each degenerate manifold is dynamically stable. Furthermore, we study a configuration with spatially localized nonlinearity, identifying an exact reflectionless state under specific conditions. Using two numerical approaches, we map the transmission input-output response of the model with spatially localized nonlinearity and identify a bistable window with hysteresis. For the parameter set studied, the exact reflectionless state coincides with the upper turning point of the $\mathrm{S}$-shaped response curve. Taken together, our analytical and numerical results show bistable transmission in the RM-based nonlinear-scattering models considered here. Given that RM potentials are experimentally feasible within ultracold atomic systems and engineered photonic lattices, our theoretical predictions could be validated on these platforms.

Two-dimensional spectroscopy (2DS) is a powerful ultrafast technique for probing electronic and vibrational dynamics in complex microscopic systems. Extracting detailed information on system dynamics and system-bath interactions from 2DS experiments requires precise theoretical simulations for comparison, which motivates the development of numerically exact and computationally efficient simulation approaches. Here, we propose a quantum-simulation approach for 2DS based on the bath-engineering technique, which has been successfully employed in quantum simulations of open quantum dynamics. To demonstrate our approach, we first simulate the 2DS of a driven four-level system in chiral enantiodetection, where we also assess the applicability of the center-line slope method for extracting time correlation functions from the 2DS. We further apply our approach to the 2DS of $\mathrm{Rh}{\left(\mathrm{CO}\right)}_2{\mathrm{C}}_5{\mathrm{H}}_7{\mathrm{O}}_2$ dissolved in chloroform, where the results reproduce the main spectral patterns observed in experiments. Our work provides a numerically exact and efficient framework for simulating 2DS, and can offer additional insight into the dynamics of open quantum systems.

We construct a quantum theory of light in nonlinear dielectric media with dispersion and absorption. We employ a mesoscopic model for the light-matter interaction that includes a fourth-order nonlinearity in the material response. Quantization is performed by constructing an effective action in a path-integral formalism by integrating out matter and bath degrees of freedom. We show how a nonlinear response function associated with Kerr nonlinearity is obtained through the model, and after full field quantization, we derive the Feynman rules from this theory.

The dynamic Stark effect and Autler-Townes splitting (ATS) are hallmarks of driven two-level systems. We establish a direct correspondence between these quantum phenomena and the parametric normal mode splitting in coupled classical oscillators. This identifies a second-subharmonic ATS under a two-tone parametric drive. We find excellent agreement between the theory and the vibrations of a nanomechanical two-mode system, capturing both the fundamental and second-subharmonic ATS, and allowing quantitative extraction of the modal coupling irrespective of the degree of modal hybridization.

Qubit leakage and loss, particularly Rydberg-induced decay during two-qubit gates, pose significant challenges to fault-tolerant quantum computing with neutral atom arrays, as they propagate to correlated errors and degrade code distance. Here, we present a hardware-efficient scheme for addressing Rydberg decay using the swap-Leakage Reduction Circuit (swap-LRC) protocol, which leverages ancilla-data qubit swaps for in-line leakage mitigation. This strategy eliminates the need for atom-species-specific midcircuit detection or additional ancillary qubits. Based on experimental detection capabilities, we present two specialized decoders. For detectable leakage or loss (e.g., in ${}^{171}\mathrm{Yb}$), our Located Decoder achieves a high threshold of 2.33% per cnot gate and an improved error distance, significantly outperforming conventional Pauli error models. More interestingly, for scenarios where only one error type is detectable (e.g., atom loss for ${}^{87}\mathrm{Rb}$), our Critical Decoder specifically targets and mitigates the most detrimental critical faults caused by correlated leakage, achieving an error distance comparable to standard Pauli errors. Our findings offer insights for handling complex non-Pauli errors for neutral atom quantum computation.

Current studies about the continuous-variable systems in non-Hermitian quantum mechanics heavily revolved around the singularities in the eigenspectrum by mimicking their discrete-variable counterparts. Discussions over the nonunitary features in the time evolution are growing and yet limited in scalability and controllability. We develop here a general theory to control an arbitrary number of bosonic modes under the time-dependent non-Hermitian Hamiltonian. Far beyond the subspace of few excitations, our control theory operates in the Heisenberg picture and exploits the gauge potential underlying the instantaneous frames rather than the eigenspectrum. In particular, the instantaneous frames are defined by time-dependent ancillary operators as linear combinations of the laboratory-frame operators, while the associated gauge potential arises from the unitary transformation connecting the time-dependent and stationary ancillary frames. We find that the upper triangularization condition of the non-Hermitian Hamiltonian's coefficient matrix in the stationary ancillary frame gives rise to two nonadiabatic passages in both bra and ket spaces and also the exact solutions of the time-dependent Schrödinger equation. At the end of these passages, the probability conservation of the system wave function can be automatically restored without brute-force normalization. Our theory is exemplified by perfect and nonreciprocal state transfers in a cavity magnonic system under the non-Hermitian Hamiltonian rigorously derived from the Lindblad master equation with all quantum-jump terms retained. Under certain conditions, the perfect state transfer holds for arbitrary initial states and is irrelevant to both parity-time symmetry of the coefficient matrix and exceptional points of the eigenspectrum. The nonreciprocal transfer is consistent with the coherent perfect absorption. Our work promises a first-principles approach for the coherent control over non-Hermitian continuous-variable systems.

In this work, we consider two-sender, one-receiver communication over a discrete memoryless multiple-access channel without feedback, where two senders may cooperate on channel coding by using preshared resources, such as shared randomness, quantum states and measurements, or nonlocal correlations. We present the capacity region when senders employ cooperative encoding with quantum and nonlocal resources, extending beyond shared randomness, and derive a sum rate that serves as a lower bound to the sum capacity; the lower bound is computable by exploiting specific strategies. We also compute the sum capacities for two instances. One is when senders apply local resources for cooperative encoding. The other is when senders exploit nonclassical resources for encoding against channels constructed by referring to nonlocal games; in this way, correlated noise other than independent errors occurs on code words. Comparing the exact sum capacities and lower bounds, we show that nonlocal and quantum resources for cooperative encoding enable higher sum capacities over local ones. The Clauser-Horne-Shimony-Holt and magic square games are considered for constructing multiple-access channels, and we demonstrate the usefulness of nonlocal and quantum resources to achieve higher-sum capacities.

We present a compact, ionization-based detector for the state-selective and spatially resolved measurement of individual Rydberg atoms located in the vicinity of an atom chip. The system combines an electrostatic lens system for guiding charged particles with an array of channel electron multipliers (CEMs) capable of detecting both ions and electrons produced by ionization. Designed for quantum information applications, this device enables the detection of correlations between spatially separated Rydberg qubits by guiding charged particles from different positions onto the $2\times 2$ CEM array. The ion-optical magnification defines the particle trajectories and, together with the detector geometry, determines the minimal atom separation that can be resolved. The imaging system achieves a total magnification above 12 and up to 200 along a single axis while maintaining low aberrations. We characterize the performance of the system using a charged particle trajectory simulation software and discuss how a coincidence measurement of ions and electrons can be used to calibrate the detection efficiency. This detector enables high-fidelity measurement of multiple Rydberg atoms and is well suited for applications in cavity-mediated quantum gates.

We investigate the optical force and torque density in relation to the symmetry of dielectric waveguides and reveal a net transverse bulk force associated with eigenmode asymmetry. An estimate of this force under readily realizable conditions indicates that the effect is testable with commonly available equipment. Upon experimental verification, force regulation based on asymmetry could provide a foundation for the optomechanical control of waveguide systems, thereby impacting various optical device technologies, including switches, couplers, and isolators, which would be useful in integrated optical systems.