High-fidelity quantum operations require the system dynamics to be strictly confined to the computational subspace. In practice, however, control fields inevitably couple to leakage levels, giving rise to quantum state leakage that significantly reduces the fidelity of the operation. To address this challenge, we propose a general strategy for actively suppressing leakage errors by applying small, static offsets to tunable system parameters. This approach systematically mitigates leakage's detrimental impact on quantum control, without modifying the original control framework or incurring additional time overhead. By avoiding the need for extra suppression pulses or complex optimization procedures altogether, it offers a streamlined solution for leakage compensation while remaining fully compatible with subsequent optimal control techniques. Numerical validation conducted on superconducting quantum circuits demonstrates effective leakage suppression, enabling high-fidelity single-qubit gates, precise control of two-qubit interactions, and perfect state transfer in multilevel systems. Moreover, when integrated with optimal control techniques, our approach also allows for the cooperative suppression of both leakage errors and residual crosstalk. Therefore, this work provides a feasible technical pathway toward the low error thresholds required for fault-tolerant quantum computation.

We have studied low-energy mutual neutralization in reactions of ${\mathrm{Si}}^{-}$ with ${\mathrm{Na}}^{+}$ and with ${\mathrm{K}}^{+}$ ions at the merged-beam double ion-beam storage-ring facility DESIREE. We made measurements with and without a significant fraction of the ${\mathrm{Si}}^{-}$ ions in the metastable ${}^{2}D$ level. The latter was achieved by state-selective photodetachment. The data reveal contributions from spin-forbidden mutual-neutralization reactions, i.e., violations of Wigner's spin-conservation rule. For the ${\mathrm{Na}}^{+}+{\mathrm{Si}}^{-}$ case, the dominating such reaction channel is obscured when metastable ${\mathrm{Si}}^{-}$ ions are present in the beam.

Polyatomic molecules are projected to be powerful tools in the search for physics beyond the Standard Model (BSM), including new CP-violating (CPV) interactions and ultralight dark-matter (UDM) particles [I. Kozyryev et al., Phys. Rev. A 103, 043313 (2021); Phys. Rev. Lett. 119, 13302 (2017)]. Certain degrees of freedom present in polyatomic molecules enhance the sensitivity of these searches, as well as reject systematic errors, but necessitate extensive high-precision spectroscopy to identify pathways for optical cycling and quantum state readout. Here we show how a magneto-optical trap can be used to locate weak optical transitions and identify rovibronic states for optical cycling and quantum control. We demonstrate this spectroscopic approach with strontium monohydroxide (SrOH), which is a candidate for both CPV and UDM searches [Z. D. Lasner et al., Phys. Rev. Lett. 134, 083401 (2025); I. Kozyryev et al., Phys. Rev. A 103, 043313 (2021); Phys. Rev. Lett. 119, 13302 (2017)]. We identify two repumping transitions in SrOH and implement them in a deeper optical cycle to achieve 32400(4700) trapped molecules, which is a 4.5-fold increase over the previous, shallower cycle. In addition, we determine the energy spacing between the ${\tilde{X}}^2{\mathrm{\Sigma }}^{+}\left(200\right)$ and ${\tilde{X}}^2{\mathrm{\Sigma }}^{+}\left({03}^{1}0\right)$ vibrational manifolds of SrOH, confirming the existence of numerous low-frequency rovibrational transitions that are sensitive to temporal variations of the proton-to-electron mass ratio, a predicted effect of the existence of UDM.

We rigorously derive the formula of the coherent-population-trapping (CPT) resonance profile by solving the Liouville equation for the density matrix in a four-level double-$\mathrm{\Lambda }$ scheme excited by a bichromatic light field. We demonstrate that the CPT resonance profile can be expressed as the sum of a symmetric and an antisymmetric Lorentz function, where the relative weights depend on the one-photon detuning. Additionally, we explicitly resolve the ac Stark shift and the line-shape-asymmetry-induced shift from the CPT resonance formula. Our theoretical calculations, based on a four-level double-$\mathrm{\Lambda }$ scheme for the $(-1,1)$ CPT resonance between ground states of $|F=3,m=-1\rangle$ and $|F=4,m=1\rangle$, successfully reproduces the observed resonance profile and light shifts under experimental conditions involving $\mathrm{lin}\parallel \mathrm{lin}$ polarization on the $D_1$ line of ${}^{133}\mathrm{Cs}$ atoms. Furthermore, the dependence of the light shift on the one-photon detuning is explained by our theoretical framework.

Ultracold atoms loaded in a quasiperiodic optical lattice offer an ideal platform to study localization. Examples include the Anderson insulator, the Bose glass phase, and many-body localization. An intriguing prospect is to investigate the dynamical localization process in a quasiperiodic optical lattice. Precision control over lattice depth, interaction strength, and filling factor enables the exploration of various correlated and fragmented phases in a finite periodic lattice. We investigate the system's dynamics when the secondary incommensurate lattice is abruptly switched on. To obtain the full time evolution of the many-body Schrödinger equation, we employ the multiconfigurational time-dependent Hartree method for bosons. The many-body dynamics is analyzed through distinct measures of the Glauber correlation functions and dynamical fragmentation. Our study reveals four distinct scenarios of localization process in the nonequilibrium dynamics. Weakly interacting nonfragmented superfluid exhibits the collapse-revival dynamics of localization. In contrast, a fragmented superfluid exhibits dynamical Mott localization. A strongly correlated, fully fragmented Mott state shows a subtle competition with localization introduced by the secondary lattice that merely melts the Mott correlations. Interestingly, in the fermionized Mott regime, where the density in each well is fragmented, the intradimer correlations exhibit unexpected robustness. These findings provide insights into many-body correlation dynamics and localization mechanisms in quasiperiodic lattices, paving the way for engineering exotic quantum behaviors in ultracold atomic systems in a quasiperiodic lattice.

Time photonic crystals have attracted growing attention in recent years owing to their abilities to enable broadband field enhancements, e.g., free-space electromagnetic waves, dipolar emissions, free-electron radiation, etc. While the non-Hermitian nature of time photonic crystals is primarily attributed to their dependence on external temporal modulations, the constituent materials are oftentimes assumed to be Hermitian. How the material-induced non-Hermiticity interplays with the intrinsic non-Hermitian dynamics of time photonic crystals remains rarely explored. In this work we demonstrate that the non-Hermiticity arising from the bianisotropic electromagnetic response of materials introduces a mechanism to manipulate the localization of temporal bulk and edge states in time photonic crystals. To be specific, the temporal bulk states in our configurations exhibit remarkable attenuation or amplification, which is theoretically predicted by extending the generalized Brillouin zone framework to the temporal domain. Our analysis reveals that the attenuation or amplification strength, quantified by the temporal penetration depth, is directly governed by electromagnetic constitutive parameters. By appropriately tuning these parameters, we uncover phenomena including broadband temporal localization—the collective concentration of energy toward a certain time moment and delocalized temporal edge states.

We study the effects of anisotropic counterrotating interactions in two coupled self-sustained quantum oscillators. Counterrotating coupling explicitly breaks the continuous $\mathrm{U}\left(1\right)$ symmetry of the system, driving a symmetry-breaking bifurcation of the quantum limit cycle into an oscillation death steady state in the Wigner function. By analyzing the power spectrum and relative-phase distribution, we show that this anisotropy suppresses bistable phase locking through the decomposition of dressed-state hybridization. For detuned oscillators, symmetry breaking produces mode-dependent oscillation death configurations and intermediate states absent in the identical case. While counterrotating interactions alone do not induce synchronization, their interplay with weak coherent exchange can reshape phase-locking dynamics. We further show that strong nonlinear damping destabilizes counterrotation-induced oscillation death and restores oscillatory dynamics via a noise-mediated quantum revival. Our results establish counterrotating interactions as a powerful control mechanism in quantum oscillators.

We investigate resource nongenerating operations in both static and dynamical quantum resource theories. For the static scenarios, we derive a sufficient condition for state transformations under resource nongenerating operations. Then we construct a dynamical resource theory where resource nongenerating operations constitute the set of free operations, and we propose an axiomatic approach to quantify the dynamical resource. We further analyze the erasure of the dynamical resources. As applications, we establish bounds on the rate of state conversions under resource nongenerating operations in a generic convex resource theory and obtain capacity bounds for classical communication tasks assisted by dynamical coherence. Our results clarify the key roles of resource nongenerating operations in quantum information processing tasks.

Battery capacity is a crucial performance metric for quantum batteries, and the exploration of methods to enhance battery capacity is of great importance for practical application. We propose a memory-assisted battery model and demonstrate that the battery capacity can be improved by performing either projective measurements or general positive operator-valued measures on the memory. It is found that the maximum gain in battery capacity from projective measurements is linked to the presence of quantum correlations. For quantum-classical states, the maximum gain is attained by projective measurements. We further extend the framework to weak measurement, and prove that its performance cannot surpass that of projective measurement. However, under certain conditions, selective weak measurement could outperform projective measurement in enhancing battery capacity. These findings are illustrated in a two-qubit state, which serves as a concrete example to exhibit how measurement schemes can be chosen to optimize battery capacity.

The quantum extreme learning machine (QELM) is an emerging hybrid quantum machine learning framework that leverages quantum system dynamics to enhance classical models. However, a QELM can suffer from the exponential concentration problem, where excessive entanglement reduces model expressivity. In this work, we gain insight into this challenge and demonstrate how tensor-network methods, specifically the time-dependent variational principle with matrix product state (MPS), can efficiently simulate quantum systems while controlling entanglement and mitigating exponential concentration. Using numerical experiments on the Modified National Institute of Standards and Technology dataset, we show that time-evolving an MPS system modeled as a chain of Rydberg atoms produces high-quality data embeddings with low classical computational overhead. Our findings indicate that exact simulation of quantum dynamics is not necessary for strong machine learning performance; even approximate quantum embeddings can yield competitive results. Furthermore, we observe that both increased disorder in the quantum state achieved by tuning Hamiltonian parameters and careful control of entanglement directly correlate with improved model accuracy, highlighting the importance of these factors in optimizing QELM performance.

Stochastic unravelings allow one to efficiently simulate open system dynamics, yet their application has traditionally been restricted to master equations in the Schrödinger picture, which preserve both Hermiticity and trace. In this work we introduce a general framework that extends piecewise-deterministic unravelings to the Heisenberg picture and arbitrary trace-nonpreserving master equations, requiring only positivity and Hermiticity of the dynamics. Our approach includes, as special cases, unravelings of arbitrary dynamics in the Heisenberg picture, evolutions interpolating between fully Lindblad and non-Hermitian Hamiltonian generators, and equations employed in the derivation of full counting statistics, for which we show it can be used to obtain the moments of the associated probability distribution. The framework is suitable for both trace-decreasing and trace-increasing processes through stochastic disappearance and replication of the stochastic realizations, and it is compatible with different unraveling schemes and with reverse jumps in the non-Markovian regime.

Bosonic codes have seen a resurgence in interest for applications as varied as fault-tolerant quantum architectures, quantum enhanced sensing, and entanglement distribution. Cat codes have been proposed as low-level elements in larger architectures, and the theory of rotationally symmetric codes more generally has been significantly expanded in the recent literature. The fault-tolerant preparation and maintenance of cat-code states as a standalone quantum error correction scheme remains, however, limited by the need for robust state preparation and strong intermode interactions. In this work, we consider the teleportation-based correction circuit for cat-code quantum error correction. We show that the class of acceptable ancillary states is broader than is typically acknowledged, and exploit this to propose the use of many-component bridge states, which, though not themselves in the cat-code space, are nonetheless capable of syndrome extraction in the regime where nonlinear interactions are a limiting factor.

We present high-resolution measurements of $4f–3d$ x-ray transitions in Cr-like tungsten ions conducted at Shanghai Electron Beam Ion Trap (EBIT). These previously unresolved lines within the $5.195–5.260\AA$ wavelength range are relevant to tokamak plasma diagnostics. High-resolution measurements using a flat Si (111) crystal spectrometer yielded experimental wavelengths with an accuracy of approximately 40 ppm. The agreement between the measured spectra and those theoretically simulated from Flexible Atomic Code calculations and collisional-radiative modeling supported the line identifications. For the seven identified lines, the average difference between experimental and theoretical wavelengths is around 132 ppm. In Maxwellian fusion plasmas, these Cr-like ${\mathrm{W}}^{50+}$ lines are predicted to maintain a stable profile similar to the profile observed in the EBIT. Additionally, some emissions from higher-charged tungsten were observed but remain unassigned. These measurements provide valuable benchmarks for both fusion plasma diagnostics and the validation of challenging atomic structure calculations of highly charged ions with open $3d$ subshell.

Tunnel ionization-assisted laser-induced electron diffraction (TI-LIED) has been successfully demonstrated as an effective technique for distinguishing structural isomers such as butane and isobutane [C.-H. Yuen et al. (unpublished)]. The inclusion of the tunnel ionization rate becomes increasingly important for larger molecules, where it significantly influences the scattering signal. In this work we begin by revisiting prior studies on two stereoisomers, 1,2-dichloroethylene (${\mathrm{C}}_2{\mathrm{H}}_2{\mathrm{Cl}}_2$) and 2-butene (${\mathrm{C}}_4{\mathrm{H}}_8$), which were previously shown to be distinguishable through their high-harmonic generation (HHG) spectra. We show that TI-LIED amplifies the scattering signal by different amounts across these isomers, producing strong contrast that peaks at backscattering, and offering a simpler, more direct alternative to HHG-based methods. Next, we demonstrate that TI-LIED has broader applicability beyond the identification of isomers. To illustrate this, we apply the method to two additional scenarios. The first examines structurally similar, but nonisomeric, molecules. An example used here is acetylene and diacetylene. TI-LIED successfully differentiates these molecules, highlighting its potential for resolving closely related molecular structures. The second case features dynamic molecules. We use the symmetric N-N stretching mode of ${\mathrm{N}}_2{\mathrm{O}}_4$ as an example. As the N-N bond length ($R_{NN}$) varies, the backscattering differential cross section oscillates strongly with $R_{NN}$ with the inclusion of TI rate, clearly reflecting the underlying structural change. With the progression of molecular imaging toward more complex species, TI-LIED is expected to become an increasingly important tool for structural analysis.

We theoretically study the double ionization of helium atom induced by an ultrashort extreme ultraviolet (XUV) pulse with the photon energy above the double-ionization threshold in the presence of an infrared (IR) laser pulse. By numerically solving the reduced-dimensional time-dependent Schrödinger equation (TDSE), we obtain the joint energy spectra of the two photoelectrons, in which peak splittings are observed both in the main band where one XUV photon is absorbed and in the sidebands where additional IR photons are either absorbed or emitted. A simple laser-assisted dynamic interference (LADI) model, based on the strong-field approximation (SFA) and neglecting the electron-electron correlation, accurately reproduces the numerical TDSE results regarding the peak splittings in the total energy spectra. Additionally, peak-splitting structures arising from the dynamic multiphoton interference (DMPI) mechanism are identified in the joint energy spectra. The DMPI is revealed by excluding the key LADI phase term in the SFA formula. We find that the DMPI is sensitive to the energy sharing between the two photoelectrons, and its contribution to peak splitting is likely smeared out in the total energy spectrum.

Lithium niobate on insulator (LNOI) has emerged as an ideal platform for photonic integration due to its superior electro-optic properties, strong nonlinearities, and low optical loss. This work presents an LNOI-based TE-pass polarizer with subwavelength gratings that overcomes the critical limitations of conventional polarizers—high insertion loss (IL) and narrow bandwidth. The device consists of the input straight waveguide, the metawaveguide, and the subwavelength gratings. By designing the metawaveguide width to match the effective refractive indices, the input TM mode is converted into a TE mode and subsequently leaks laterally through the side subwavelength gratings. Simulation results indicate a polarization extinction ratio (PER) of 32 dB with an IL below 0.46 dB, maintaining a PER $>20\mathrm{dB}$ across a 24 nm range. Experimentally, the device achieves a 28.6 dB PER and maintains a PER $>15\mathrm{dB}$ over a 71 nm bandwidth. Notably, a cascaded configuration of three identical devices maintains an ultracompact footprint ($<660\mu \mathrm{m}$ length). This breakthrough performance establishes our design as an optimal solution for polarization management in high-density photonic integration.

We propose a high-precision weak-force sensing scheme with squeezed light and feedback control in an unresolved-sideband cavity optomechanical system. This scheme employs synergistic integration of the injection of squeezed light and measurement-based feedback control. We analyze the influence mechanism of various system parameters and examine how squeezed light and closed-loop control jointly improve the measurement sensitivity. The proposed weak-force sensing scheme could improve the signal-to-noise ratio of the weak-force measurement and reduce the added noises. It is compatible with state-of-the-art cavity optomechanical techniques and may find applications in quantum metrology, gravitational wave detection, and fundamental physics tests.

Recent explorations of quantized soliton transport in optical waveguides have thrust nonlinear topological pumping into the spotlight. In this work, we introduce a unified topological invariant applicable across both weakly and strongly nonlinear regimes. In the weak nonlinearity regime, where the nonlinear bands are well separated, the invariant reduces to the Abelian Chern number of the occupied nonlinear band. Consequently, the pumped charge is quantized to an integer value. As the nonlinearity increases, the nonlinear bands start to intertwine, leading to a situation where the invariant is expressed as the non-Abelian Chern number divided by the number of interacting bands. This could result in a fractional quantization of the pumped charge. Our unified-topological-invariant approach not only advances the understanding of the soliton dynamics but also provides implications for the future design of nonlinear topological systems.