This study explores the dual role of a squeezed reservoir in controlling the quantum phase synchronization of a driven two-level system. We first demonstrate, through a Liouvillian eigenspectrum analysis, that the squeezed reservoir can induce a stable limit cycle, transforming the passive two-level system (TLS) into a genuine self-sustained oscillator. This enables a qualitative transition from a weak “forced response” to a robust, high-quality synchronization (or entrainment). This enhancement is characterized not only by a greater degree of phase locking but also by an increased frequency selectivity, manifested as a narrower Arnold tongue. More strikingly, we reveal that the squeezing angle acts as a control parameter to actively suppress synchronization. By tuning this angle, the reservoir can drive the system into a classical mixed state, inducing a quantum synchronization blockade via the quenching of steady-state coherence. Our findings establish squeezed-reservoir engineering as a versatile strategy for actively modulating quantum synchronization, with feasible implementations in circuit quantum electrodynamics.

We study boundary time crystals (BTCs) in the presence of non-Markovian dynamics. In contrast to BTCs observed in earlier works in the Markovian regime, we show that non-Markovian dynamics can be highly beneficial for stabilizing BTCs over a wide range of parameter values, even in the presence of intermediate rates of dissipation. Notably, we also observe the emergence of higher-order limit cycles (HOLCs) for some parameter regimes. We analyze the effect of non-Markovian dynamics on BTCs and HOLCs using quantum Fisher information, time-averaged magnetization, a measure of non-Markovianity, and a dynamical phase diagram, all of which show complex behaviors with changing non-Markovianity parameters. Our studies can pave the way for stabilizing time crystals in dissipative systems, as well as lead to studies on varied dissipative dynamics on time-translational symmetry breaking.

We develop a graph-based method to study the entanglement entropy of Calderbank-Shor-Steane quantum codes. This method offers a straightforward interpretation for the entanglement entropy of quantum error-correcting codes through graph-theoretical concepts, shedding light on the origins of both the local and long-range entanglement. Moreover, it inspires a scheme for evaluating the entanglement entropy of arbitrary Calderbank-Shor-Steane quantum codes, which can be computationally advantageous when a simple graph representation is available. We illustrate the method by calculating the von Neumann entropy of subsystems in toric codes and two types of quantum low-density parity-check codes, and by comparing the scaling behavior of the entanglement entropy with respect to the subsystem size. Our method introduces a perspective for understanding the entanglement structure in quantum many-body systems.

There are processes that cannot generate entanglement but may, nevertheless, amplify entanglement already present in a system. Here, we show that a nonentangling operation can increase the Schmidt number of a quantum state only if it can generate entanglement with some nonzero probability. This is in stark contrast to the case where the parties of a quantum network are only able to control their joint state by local operations and classical communication (LOCC). There, being able to apply operations probabilistically (stochastic LOCC) does not increase the Schmidt number. Our findings show that certain nonentangling operations become entangling when specific measurement outcomes are selected. This naturally leads us to the class of stochastically nonentangling maps, which are those that cannot generate entanglement even probabilistically. Intrigued by this finding, we devise a Schmidt number for quantum channels that quantifies whether a channel can generate entanglement probabilistically. Moreover, we show that a channel is nonentangling if and only if its dual map is witness preserving—it takes entanglement witnesses to witnesses. Based on this finding, we derive inequalities whose violation signals that a process generates entanglement.

Entanglement distribution is a crucial problem in quantum information science, owing to the essential role that entanglement plays in enabling advanced quantum protocols, including quantum teleportation and quantum cryptography. We investigate strategies for distributing quantum entanglement between two distant parties through noisy quantum channels. Specifically, we compare two configurations: one where the entanglement source is placed at the midpoint of the communication line, and another where it is located at one end. For certain families of qubit channels we show analytically that the midpoint strategy is optimal. Based on extensive numerical analysis, we conjecture that this strategy is generally optimal for all qubit channels. Focusing on the midpoint configuration, we develop semidefinite programming (SDP) techniques to assess whether entanglement can be successfully distributed through the network, and to quantify the amount of entanglement that can be distributed in the process. In many relevant cases the SDP formulation reliably captures the maximal amount of entanglement which can be distributed, if entanglement is quantified using the negativity. We analyze several channel models and demonstrate that, for various combinations of amplitude damping and depolarizing noise, entanglement distribution is only possible with weakly entangled input states. Excessive entanglement in the input state can hinder the channel's ability to establish entanglement. Our findings have implications for optimizing entanglement distribution in realistic quantum communication networks.

The Petz recovery map is a central construct in quantum information theory, providing an explicit, channel-aware prescription for reversing the effects of noise. Unlike standard quantum operations, the Petz map is intrinsically dependent on a chosen reference state, which makes its physical implementation and experimental validation particularly challenging. Here, we report an experimental realization of Petz recovery maps on a nuclear magnetic resonance quantum processor using the duality quantum computing algorithm. We investigate two paradigmatic single-qubit noise models—amplitude damping and phase damping—and construct corresponding families of Petz recovery maps for varying reference states. By systematically tuning the reference state, we experimentally demonstrate the state-adapted nature of Petz recovery, observing both enhanced recovery when the reference state is well matched and fidelity degradation for mismatched choices. Our experimental results show close quantitative agreement with theoretical predictions, providing direct evidence that the Petz recovery map constitutes a physically realizable, reference-state-dependent recovery channel rather than a purely formal inverse of noise. This work bridges the gap between the abstract information-theoretic formulation of Petz recovery and its implementation on a realistic quantum platform, and establishes an experimental benchmark for testing noise-adapted recovery strategies on near-term quantum devices.

Quantum computers can efficiently solve problems which are widely believed to lie beyond the reach of classical computers. In the near-term, hybrid quantum-classical algorithms, which efficiently embed quantum hardware in classical frameworks, are crucial in bridging the vast divide in the performance of the purely quantum algorithms and their classical counterparts. Here, a hybrid quantum-classical algorithm is presented for the computation of nonperturbative characteristics of quantum field theories. The presented algorithm relies on a universal parametrized quantum circuit ansatz based on Euler and Cartan's decompositions of single- and two-qubit operators. It is benchmarked by computing the energy spectra of lattice realizations of quantum field theories with both short- and long-range interactions. Low depth circuits are provided for false vacua as well as highly excited states corresponding to mesonic and baryonic excitations occurring in the analyzed models. The described algorithm opens an additional avenue for the investigation of mass-ratios, scattering amplitudes, and false-vacuum decays in quantum field theories.

We investigate phase-resolved Ramsey-type quantum interference in photoelectron momentum distributions generated by two time-delayed, linearly polarized extreme-ultraviolet (XUV) laser pulses. The electron dynamics is studied by solving the full-dimensional time-dependent Schrödinger equation within the single-active-electron (SAE) approximation for neon. The coherent superposition of electron wave packets released by the two pulses gives rise to pronounced interference fringes in both energy-resolved spectra and angle-resolved momentum distributions. We demonstrate that the fringe positions are governed by a Ramsey phase accumulated during the interpulse delay, resulting in a linear dependence on the relative carrier-envelope phase and an inverse scaling of the fringe spacing with the delay time. By systematically varying the laser intensity, we establish that the observed modulations originate from temporal quantum interference rather than Autler-Townes splitting. A complementary short-range single-bound-state model confirms that the existence and spacing of the Ramsey fringes arise from continuum wave packet superposition. In the multi-bound-state SAE system, transient bound-bound coupling modifies the accumulated phase prior to ionization, imprinting a potential-dependent phase offset onto the interference pattern. The accumulated phase is further interpreted in terms of a dynamic Stark shift of the dressed bound states, which is quantitatively reproduced using a reduced two-level model.

Quantum emitters coupled to one-dimensional waveguides constitute a paradigmatic quantum-optical platform for exploring collective phenomena in open quantum many-body systems. For appropriately spaced emitters, they realize the Dicke model, whose characteristic permutation symmetry allows for efficient exact solutions featuring superradiance. When the emitters are arbitrarily spaced, however, this symmetry is lost and general analytical solutions are no longer available. In this work, we introduce a numerical method to study the dynamics of such systems by extending the time-dependent neural quantum state (t-NQS) framework to open quantum systems. We benchmark our approach across a range of waveguide QED settings and compare its performance with tensor-network calculations. Our results demonstrate that the t-NQS approach is competitive with other numerical methods and highlight the potential of t-NQSs for studying open quantum many-body systems out of equilibrium.

We investigate a simple model exhibiting a prethermal phase, i.e., a metastable state that emerges before full thermalization, through the framework of quantum stochastic thermodynamics. We explore the effects of quantum coherence in the energy eigenbasis of the initial state of the system on the process of heat exchange with a bath, and their contribution to entropy production as quantified by a heat-exchange fluctuation theorem. Such a relation is derived using the end-point measurement scheme, a protocol that accounts for initial quantum coherence in the statistics of energy exchanges resulting from a nonequilibrium process. We compare these results with those obtained from the widely used two-point measurement scheme, which, by construction, fails to capture such quantum effects.

Unlike classical correlations, entanglement cannot be freely shared among multiple parties. This unique feature of quantum systems is known as the monogamy of entanglement. While it holds for all multipartite pure states, its converse—weak entanglement between two parties enforces strong entanglement with a third party—occurs only under specific conditions. In particular, Hayashi and Chen [Phys. Rev. A 84, 012325 (2011)] demonstrated a qualitative version of the converse monogamy of entanglement (CMoE) for tripartite pure states by employing a hierarchy of bipartite entanglement defined through the relations among various separability criteria, and Singh and Datta [IEEE Trans. Inf. Theory 69, 6564 (2023)] later extended this notion of the CMoE from the viewpoint of distillability under one-way or two-way classical communication. In this work, we extend their results to the CMoE with broader conditions, and furthermore show that our extensions are maximal with respect to the hierarchies they considered.

Interferometric power (IP) quantifies the worst-case quantum Fisher information (QFI) achieved in a black-box interferometry, where the local encoding Hamiltonian has a fixed spectrum but an unknown eigenbasis. For classical-classical states as inputs for a two-qubit unitary gate, we adopt the maximum value of the symmetrized IP to quantify its IP-generation capability. Using the Cartan decomposition, our numerical results show that the unitary gates with the three-axis isotropic couplings can attain the maximum value of the symmetrized IP. Interestingly, IP is a more economical resource than quantum entanglement in adversarial sensing.

Ultracold neutral atoms in optical lattices are a promising platform for simulating the behavior of complex materials and implementing quantum gates. We optimize collision gates for fermionic ${}^6\mathrm{Li}$ atoms confined in a double-well potential, controlling the laser amplitude and keeping its relative phase constant. We obtain high-fidelity gates based on a one-dimensional confinement simulation. Our approach extends beyond earlier Fermi-Hubbard simulations by capturing a momentum dependence in the interaction energy. This leads to a higher interaction strength when atoms begin in separate subwells compared to the same subwell. This momentum dependence might limit the gate fidelity under realistic experimental conditions, but also enables tailored applications in quantum chemistry and quantum simulation by optimizing gates for each of these cases separately.

Continuous-variable quantum key distribution is a practical solution for secure communication, compatible with classical optical networks. The discrete modulation scheme simplifies implementation but complicates security analysis, where the shot-noise unit is a critical parameter. Traditional two-step shot-noise unit calibration is experimentally cumbersome and unsuitable for real-time systems. Here, we propose a one-time shot-noise unit calibration method for discrete-modulated continuous-variable quantum key distribution, which determines the shot-noise unit in a single step. Our approach introduces a revised detector model that treats electrical noise loss as untrusted, incorporating it into the channel. We establish the equivalence between the entanglement-based and prepare-and-measure schemes under this model and derive the corresponding positive operator-valued measure for heterodyne detection. Combining trusted-source-noise model, a complete practical security model can be achieved. Security analysis and simulations show that the proposed method achieves performance close to traditional protocols, facilitating the deployment of discrete-modulated continuous-variable quantum key distribution systems with automated, real-time calibration.

Ion-pair dissociation (IPD) usually occurs in molecular superexcited states, exhibiting complicated dynamics. Electron-impact-induced IPD is scarcely investigated, due to challenges both in the experimental measurements and data interpretation. Here, we report an experimental study of the IPD dynamics of carbon monoxide (CO) by low-energy (25–45 eV) electron impact, using an anion velocity map imaging technique. Branching ratios between the anionic yields ${\mathrm{C}}^{-}$ and ${\mathrm{O}}^{-}$ indicate a predominance of ${\mathrm{O}}^{-}$ production, while a slight enhancement of the minor product ${\mathrm{C}}^{-}$ with an increase of electron-impact energy is observed. The electron-impact energy dependences of the ${\mathrm{O}}^{-}$ and ${\mathrm{C}}^{-}$ velocity images are insignificant while they do exist at relatively low-impact energies. Moreover, the ${\mathrm{O}}^{-}$ and ${\mathrm{C}}^{-}$ velocity images exhibit distinctly different forward-backward asymmetries at a common electron energy. The electron-impact IPDs observed here are classified into an indirect process via doubly excited Rydberg states of CO and a direct process from the repulsive ion-pair states, and the ${\mathrm{O}}^{-}$ and ${\mathrm{C}}^{-}$ angular distributions are further elucidated with partial-wave analyses of quantum scattering theory.

Molecular QED theory is used to calculate one-photon absorption probabilities in magnetic systems induced by structured light. Specifically, a circularly polarized Laguerre-Gaussian beam possessing a helical phase is applied to a microscopic particle characterized by magnetic dipole and magnetic quadrupole moments. This is inspired by the helical dichroism observed in recently fabricated propeller metamolecules that was attributed to the interference of magnetic dipole and quadrupole coupling terms. Observable properties computed include rates for circular dichroism (CD), vortex dichroism (VD), and circular-vortex dichroism (CVD), with the last of these arising from the coupling of both optical spin and orbital angular momenta. To ensure no possible dichroic effects are missed, the oft-ignored longitudinal component of the magnetic field and its gradient are properly included in addition to the usual transverse part. It is found that for isotropic purely magnetic dipole species, no CD, VD, or CVD arises from the transverse field alone, while only the longitudinal field gives rise to CD but no VD. For particles described by the magnetic dipole-quadrupole cross term, all three types of differential absorption are exhibited for both a fixed configuration and randomly oriented situations. Interestingly, the dichroic phenomena depend on the interference of transverse and longitudinal optical vortex field components to manifest.

We build a minimal theoretical model to describe the opening of a gap in the dispersion of the collective excitations of a driven-dissipative condensate when the condensate phase is fixed by an additional coherent phase-locking drive. We map out the phase diagram as a function of the amplitude and frequency of the coherent drive, identifying distinct regions corresponding to different steady-state regimes. For each region, we analyze the dispersion of the collective excitations and determine whether the spectrum is gapped, with either a purely imaginary gap or a finite real part. When the coherent drive is unable to lock the condensate phase, a gapless Goldstone mode is recovered. Within the same phase diagram, we further identify regions of finite-wave-vector dynamical instability, where the condensate tends to develop a supersolid-like spatial modulation. While our theoretical framework is directly related to recent experiments with exciton-polariton condensates, it can be applied to describe the effect of external injection also in a variety of spatially extended optical parametric oscillators or laser devices.

We propose and experimentally demonstrate a method to directly measure energy dissipation for a linearly driven superfluid confined in a harmonic trap. The method relies on a perturbed version of the harmonic-potential theorem, according to which a potential perturbation—effectively acting as a stirrer—converts center-of-mass motional energy into internal energy. Energy conservation then enables a direct, quantitative determination of the dissipated energy from measurements of the macroscopic center-of-mass observables. Applying this method to a perturbed, driven Bose-Einstein condensate, we observe dissipation curves characteristic of superfluid flow, including a critical velocity that depends on the stirrer strength, consistent with previous studies. Our results are supported by mean-field simulations, which corroborate both the theoretical framework and the experimental findings.

Soliton dynamics in coupled Kerr microcavities is an important aspect of frequency comb technologies, with applications in optical communication and precision metrology. We investigate a minimal system consisting of two nearly identical coupled Kerr microresonators, each operating in the soliton regime and driven by a separate coherent beam, and analyze the mechanisms that govern their soliton interactions. In the weak-coupling regime, the system supports multiple soliton clusters characterized by distinct soliton separations and stability. Numerical simulations indicate that asymmetric perturbations can alter soliton separations or destroy these states, while the imposed pump-phase difference plays a key role in cluster selection. Together, these findings may highlight previously unexplored regimes of dissipative soliton organization and could suggest strategies for controlling soliton ensembles in integrated photonic platforms.