Microwave-to-optical transducers facilitate the distributed quantum network by combining the high-speed information-processing abilities of superconducting circuits with the long-distance, low-loss transmitting capabilities of optical photons. Besides core metrics such as high efficiency, low noise, and wide bandwidth, practical and scalable transducers also demand a compact footprint and frequency tunability. In this work, we propose an integrated and tunable transducer that combines a coplanar waveguide microwave resonator with a magno-optomechanical microcavity via flip-chip bonding. Benefiting from the broad frequency tunability of the magnon mode, the working frequency range can be tuned over several gigahertz. Through optimization of the geometry and pump powers, our design achieves a theoretical microwave-to-optical photon conversion efficiency exceeding 50% using experimentally achievable parameters, alongside a bandwidth greater than 10 kHz. An added noise near the quantum limit $(\sim 1)$ is achievable at 10 mK using lower pump powers at the cost of conversion efficiency or a pulsed-pump protocol. By merging compact integration with wide frequency tunability, this platform offers a promising pathway toward scalable quantum networks.

Light fields with partial spatial coherence are renowned for their remarkable self-reconstruction properties, which have enabled a wide range of applications, including optical imaging and particle trapping. In this paper, we extend the self-reconstruction concept to temporal-domain partially coherent pulses and investigate their reconstruction characteristics in nonlinear Kerr media. As an illustrative example, we employ a cosine-Gaussian correlated Schell-model pulse to conduct in-depth analyses. Our numerical results reveal that the obstructed pulses, with the help of the source degree of coherence, exhibit outstanding self-reconstruction properties in the nonlinear Kerr media. Although the nonlinearity can to some extent impair the self-reconstruction ability of pulses, ultrastrong self-reconstruction of the pulses can be achieved by reducing the optical coherence. Our research findings may have potential applications in image transmission and optical information processing.

We propose a scheme for manipulations of a variety of topological states in fractional optical systems through spiral modulation of the local refraction index. An analytical approximation, based on a truncated finite-mode system, and direct simulations reveal that the spiral modulation supports direct mutual conversion between eigenmodes with topological-charge difference $\mathrm{\Delta }m=1$, driven by the resonant coupling between the modes and the underlying spiral modulation. The conversion between eigenmodes with $\mathrm{\Delta }m=2$ requires involvement of an intermediary mode and precise tuning of the resonance condition. We further explore the conversion of degenerate modes under the action of azimuthal modulation. Modulated degenerate modes exhibit incomplete conversion, evolving into intermediate states with odd parity symmetry. Finally, we examine nonlinear effects on the spiral-modulation-induced mode conversion, identifying an essential nonlinearity-induced resonance-frequency shift that critically affects the conversion efficiency.

Non-Abelian braiding plays a crucial role in topological quantum computing for protecting the evolution of non-Abelian anyons. Recently, the concept of non-Abelian braiding has been introduced to classical systems for applications such as quantum logic, but the working mode was restricted to the fundamental mode. Here, we propose a scheme for realizing the classical non-Abelian braiding of coupled modes in photonic waveguides system. The Hamiltonian of the designed system is built via the interplay between two sub-Hamiltonians, where one of them enables the non-Abelian braiding, while the other one generates the coupled modes. In this way, the non-Abelian braiding of coupled modes of arbitrarily high order can be realized. We carry out numerical simulations to verify the concept for coupled modes with an order of four, including the mode switching behavior as well as the non-Abelian geometric phase. The proposed concept may lead to on-chip applications including mode division multiplexing non-Abelian braiding.

The nonequilibrium dissipative phase transition, arising from the competition of cooperative behavior and coherent field driving, discovered in the 1970s by Narducci et al. [Phys. Rev. A18, 1571 (1978)] and Walls et al. [Prog. Theor. Phys. Suppl.64, 307 (1978)], has been found to exhibit time-crystal behavior when the driving field exceeds the cooperative decay rate. This was seen through the study of the eigenvalues of the Liouvillian superoperator that describes the joint effect of drive and cooperativity. The cooperative decay depends on the nature of the reservoir correlations. If the reservoir correlations have phase-sensitive behavior, then the eigenvalues of the Liouvillian will be different. We investigate the time-crystal behavior of the nonequilibrium dissipative phase transitions under the influence of a squeezed vacuum reservoir. We analyze the steady-state phase diagram as a function of the control parameter and demonstrate that increasing the squeezing strength sharpens the dissipative phase transition. Spectral analysis of the Liouvillian reveals gap closings and the emergence of purely imaginary eigenvalues in the thermodynamic limit, indicating the time-crystal phase. We find that the real parts of subleading eigenvalues exhibit nonmonotonic behavior with increasing squeezing, reflecting the sensitivity of relaxation dynamics to the reservoir properties. Time-domain simulations confirm that the oscillation frequencies correspond to the imaginary parts of the Liouvillian eigenvalues. We also present results on quantum fluctuations in the time-crystal phase. Our results call attention to the study of time crystals in models of cooperativity based on engineered environments.

In this work we explore the implications of applying the formalism of symplectic geometry to quantum mechanics, particularly focusing on many-particle systems. We extend the concept of a symplectic indicator of entanglement, originally introduced by Sawicki et al., Commun. Math. Phys. 305, 441 (2011), to these complex systems. Specifically, we demonstrate that the restriction of the symplectic structure to manifolds comprising all states characterized by isospectral reduced one-particle density matrices $M_{\mu \left(\psi \right)}^0$ exhibits degeneracy for nonseparable states. We prove that the degree of degeneracy at any given state $|\phi \rangle \in M_{\mu \left(\psi \right)}^0$ corresponds to the degree of degeneracy of the symplectic form $\omega$ when restricted to the manifold of states that are locally unitary equivalent with $|\phi \rangle$. Additionally, we provide a physical interpretation of this symplectic indicator of entanglement, articulating it as an inherent ambiguity within the associated classical dynamical framework. Our findings underscore the pivotal role of symplectic geometry in elucidating entanglement properties in quantum mechanics and suggest avenues for further exploration into the geometric structures underlying quantum state spaces.

Prethermal discrete time crystals (DTCs) are a novel phase of periodically driven matter that exhibits robust subharmonic oscillations without requiring disorder. However, previous realizations of prethermal DTCs have relied on the presence of polarization, either spontaneous or induced. Here we introduce a class of prethermal DTCs termed “unpolarized prethermal discrete time crystals” (UPDTCs) that arise without any uniform or staggered polarization and propose an experiment to observe them in current trapped-ion quantum simulators. By studying a model of trapped ions using a quantum circuit simulator, we demonstrate that robust period-doubled dynamics can persist in the autocorrelation function of the staggered magnetization, even though its expectation value does not exhibit such dynamics. The period-doubled dynamics is not explained by the classical picture of flipping spins but by quantum fluctuations. We establish that UPDTCs are exponentially long-lived in the high-frequency driving regime, a hallmark of prethermalization. These results expand the known phenomenology and mechanism of prethermal time crystals and underscore the role of quantum effects in stabilizing novel nonequilibrium phases.

We investigate the extremality of stabilizer states to reveal their exceptional role in the space of all $n$-qubit and $n$-qudit states. We establish uncertainty principles for the characteristic function and the Wigner function of states, respectively. We find that only stabilizer states achieve saturation in these principles. Furthermore, we prove a general theorem that stabilizer states are extremal for convex information measures invariant under local unitaries. We explore this extremality in the context of various quantum information and correlation measures, including entanglement entropy, conditional entropy, and other entanglement measures. Additionally, leveraging the recent discovery that stabilizer states are the limit states under quantum convolution, we establish the monotonicity of the entanglement entropy and conditional entropy under quantum convolution. These results highlight the remarkable Gaussian properties of stabilizer states in qudit and qubit systems.

In this work, we explore a new approach to designing both algorithms and error detection codes for preparing approximate ground states of molecules. We propose a classical algorithm to find the optimal stabilizer state by using excitations of the Hartree-Fock state, followed by constructing quantum error-detection codes based on this stabilizer state using codeword-stabilized codes. Through various numerical experiments, we confirm that our method finds the best stabilizer approximations to the true ground states of molecules up to 36 qubits in size. Additionally, we construct generalized stabilizer states that offer a better approximation to the true ground states. Furthermore, for a simple noise model, we demonstrate that both the stabilizer and (some) generalized stabilizer states can be prepared with higher fidelity using the error-detection codes we construct. Our work represents a promising step toward designing algorithms for early fault-tolerant quantum computation.

Quantum error mitigation (QEM) schemes have greatly enhanced the performance of quantum computers, mostly by reducing errors caused by interactions with the environment. Nevertheless, the presence of coherence errors, typically arising from miscalibration and interqubit crosstalk, is a significant challenge to the scalability of quantum computing. Such errors are often addressed using a refined Pauli twirling scheme called randomized compiling (RC) that converts the coherent errors into incoherent errors that can then be mitigated by conventional QEM. Unfortunately for multiqubit gates, RC is restricted to Clifford gates such as cnot and cphase. However, it has been demonstrated experimentally that a direct implementation of multiqubit non-Clifford gates, i.e., without using multiqubit Clifford gates, has reduced the depth of the circuit by a factor of four and more. Recently, a framework called pseudotwirling (PST) for treating coherent error in multiqubit non-Clifford gates has been introduced and experimentally demonstrated. We show analytically that a higher-order correction to the existing PST theory yields an over-rotation coherent error generated by the PST protocol itself. This PST effect has no analog in RC. Although the small induced over-rotation can amount to a significant coherent error in deep circuits, we explain why it does not degrade the performance of the gate. Interestingly, we find that a simplified twirling scheme that was introduced and exploited experimentally by Kim et al. also displays an induced over-rotation. We study the conditions under which the two twirling schemes display the same over-rotation behavior.

We probe dissociative electron attachment (DEA) to methyl iodide, ${\mathrm{CH}}_3\mathrm{I}$, using the velocity-map imaging (VMI) technique. Our DEA-VMI spectrometer allows for preparation of the incident electron beam at electron energies low enough to record the images of the exothermic ${\mathrm{I}}^{-}$ production channel. A clear forward-backward asymmetry visible in the angular distributions is attributed to contributions of different partial waves which are controlled by partial widths of the involved resonant state. This coupling of partial waves is facilitated primarily by the dipolar field of the target molecule.

Chiral polaritonics offers promising opportunities to selectively manipulate molecular species based on their handedness by harnessing unique interaction pathways offered by strong coupling in cavity QED. While significant progress has been made in understanding the fundamental mechanisms of enantiomer selectivity, many existing studies focus on perfectly chiral cavities that contain only one type of enantiomer. Here, we investigate a scenario of imperfect cavities containing varying mixtures of enantiomers. Using a generalized Hopfield-type model, we systematically explore how the degree of enantiomeric mixing and cavity imperfections affect chiral selectivity. Our analysis includes both an examination of the cavity's eigenmode structure and a quantitative assessment of differential energy transfer into specific enantiomeric species. We demonstrate that both cavity imperfections and the presence of enantiomer mixtures profoundly modify the polaritonic dispersion. We also highlight that pushing the system into the deep strong coupling regime—by increasing molecular concentration—can decrease the efficiency of energy transfer to matter modes. These findings emphasize that precise cavity design and detailed consideration of enantiomeric composition are essential for achieving optimal chiral selectivity in practical cavity QED systems.

The Mpemba effect has garnered growing attention and diverse interpretations within the realm of quantum physics. Recently, Medina et al. [Phys. Rev. Lett. 134, 220402 (2025)] introduced the ergotropic Mpemba effect in quantum batteries governed by Markovian dynamics, highlighting the anomalous phenomenon where batteries in higher ergotropy states discharge faster than those in lower ergotropy states. Building on this foundation, our research proposes an all-optical scheme to realize the ergotropic Mpemba effect in open quantum systems, and further investigates its implications in systems exhibiting non-Markovian dynamics. We find that the ergotropic Mpemba effect persists in non-Markovian dynamics. In the strong non-Markovian regime, prior to the occurrence of the ergotropic Mpemba effect, the ergotropy evolution shows multiple crossings, which we refer to as the quasiergotropic Mpemba effect. Moreover, we derive the analytical solution for the critical point at which the ergotropic Mpemba effect occurs, and we establish the necessary conditions for this effect to emerge. Finally, we propose an experimental scheme based on continuous-variable quantum circuits to realize our theoretical prediction.

Quantum state diffusion is a framework within which measurement may be described as the continuous and gradual collapse of a quantum system to an eigenstate as a result of interaction with its environment. The irreversible nature of the quantum trajectories that arise may be characterized by the environmental stochastic entropy production associated with the measurement. We consider a system of two spin-1/2 particles undergoing either single-particle measurements or measurements of the total $z$-spin component $S_z$. The mean asymptotic rates of environmental stochastic entropy production associated with collapse can depend on the eigenstate of $S_z$ selected and on the initial state of the system, offering an additional avenue for characterizing quantum measurement.

Quantum Kerr parametric oscillators (KPOs) are systems out of equilibrium with a wide range of applications in quantum computing, quantum sensing, and fundamental research. They have been realized in superconducting circuits and photonic platforms. In this work, we explore the onset of ground-state and excited-state quantum phase transitions in KPOs, focusing on the role of the phase-space rotational symmetry when the driving frequency is $\mu$ times the oscillator's natural frequency, specifically for $\mu =1,2,3,4$. These cases are experimentally accessible in superconducting circuits, where the Floquet quasienergy spectrum can also be studied as a function of tunable control parameters. Using the classical Hamiltonian of the system, we identify the stationary points associated with quantum phase transitions and analyze the emergence of both real and avoided level crossings, examining their influence on the energy spectrum and tunneling dynamics. Our findings provide insights into the engineering of robust quantum states, quantum dynamics control, and onset of quantum phase transitions with implications for critical quantum sensing.

In the scenario of the probe-ancilla interaction, we propose a quantum metrology protocol by the unconditional measurement on the ancillary qubit after an optimized period of joint evolution from a product state. Its key element is the construction of two parallel evolution paths by the measurement that can transform the probe system (a spin ensemble) from an eigenstate of a collective angular momentum operator $|j,m\rangle$ to a superposed state $\left(\right|j,m\rangle +|j,-m\rangle )/\sqrt{2}$. With synchronous parametric encoding and qubit measurement, the quantum Fisher information about the phase encoded in the probe system with optimized initial states can exactly attain the Heisenberg scaling $N^2$ with respect to the probe size (spin number) $N$. The quadratic scaling behavior is not sensitive to the imprecise control over the joint evolution time, the time delay between encoding and measurement, and the coherence in the probe ensemble or the ancillary system that would be degraded by local dephasing. The classical Fisher information of the spin ensemble is found to saturate with its quantum counterpart, irrespective of the idle joint evolution after the parametric encoding. We suggest that both Greenberger-Horne-Zeilinger (GHZ)-like states and nonlinear Hamiltonian are not necessary resources for exceeding the standard quantum limit in metrology precision since in our protocol even thermal states can hold an asymptotic quadratic scaling.

The difficulty of training variational quantum algorithms and quantum machine learning models is well established. In particular, quantum loss landscapes are often highly nonconvex and dominated by poor local minima. While this renders their training NP hard in general, efficient heuristics that work well for typical instances may still exist. Here we propose a protocol that uses a targeted noise injection to smooth and regularize quantum loss landscapes. It works by exponentially suppressing the high-frequency components in the Fourier expansion of the quantum loss function. The protocol can be efficiently implemented in both hardware and simulations. We observe significant and robust improvements of solution quality across various problem types. Our method can be combined with existing techniques mitigating the local minima, such as the quantum natural gradient optimizer, and adds to the toolbox of methods for optimizing quantum loss functions.