The Uhlmann phase extends the concept of geometric phases to mixed quantum states through a parallel-transport condition on purification amplitudes, but its experimental realization has so far required sophisticated quantum platforms with carefully engineered auxiliary degrees of freedom. In this work, we reformulate the Uhlmann parallel-transport condition as a linear matrix differential equation and vectorize it to obtain an effective dynamical generator. This generator can be directly mapped onto the admittance matrix of a classical RC circuit, thereby translating the Uhlmann dynamics into the evolution of circuit node voltages. We illustrate the mapping using the equatorial-loop model and, via a rotating-frame transformation followed by a real decomposition, derive a time-independent, real-valued dynamical system suitable for analog implementation. lt spice simulations of the resulting active RC network faithfully reproduce the Uhlmann geometric phase and its topological transition at the critical purity, demonstrating that classical electrical circuits offer a simple and accessible platform for probing mixed-state geometric phases.

This work addresses the fundamental question concerning the nature of quantum states, specifically to what extent they represent an agent's knowledge about the system, that is, is epistemic in nature. We show that, despite the existence of the Kochen-Specker model, which is a maximally $\psi$-epistemic model for single-qubit systems when projective measurements are employed, no maximally $\psi$-epistemic model can reproduce statistics arising out of nonprojective measurements on a pair of single-qubit states. This has been done in an experimentally robust way using only two pure single-qubit states and their equal mixture, by constructing a two-input, three-output game called risk aware distinguishability (RAD) and generalizing the notion of epistemic and quantum overlaps using RAD. Furthermore, we maximize the difference of generalized overlaps instead of minimizing their ratio and in the process point out why that is a stricter criterion for refuting $\psi$-epistemic models.

Nonlocality can be witnessed either through Bell-inequality violations or through logical contradictions such as Hardy's paradox. In the bipartite two-input two-outcome scenario, these two routes have distinct geometric behavior: Clauser-Horne-Shimony-Holt maximal correlations are exposed points of the quantum set, whereas known Hardy-type self-testing correlations on the no-signaling boundary are nonexposed. Here we show that this bipartite intuition fails in the tripartite two-input two-outcome scenario. We study the tripartite instance of a multipartite Hardy-type paradox and prove that the correlation attaining the maximal Hardy success probability self-tests the Greenberger-Horne-Zeilinger (GHZ) state and the associated measurements. Although this correlation lies on the no-signaling boundary, we show that it is an extremal and exposed point of the quantum correlation set. Moreover, it coincides with the correlation attaining the maximal violation of the Mermin inequality. Thus, in the tripartite GHZ scenario, the logical-paradox and Bell-inequality routes to nonlocality select the same exposed quantum boundary point. We also establish a robust version of the self-test, showing that small deviations from the ideal Hardy constraints imply quantitative closeness to the target state and measurements. Our results reveal a qualitative geometric difference between bipartite and tripartite Hardy-type nonlocality and suggest a broader investigation of exposedness for multipartite Hardy correlations in the multiparty setting.

Autonomous stabilization of many-body quantum states requires a mechanism that continuously removes stabilizer violations without relying on measurement and feedback. Here we develop a Floquet-Lindblad framework for scalable stabilizer pumping in neutral-Rydberg-atom arrays. Periodically modulated Rydberg excitation selectively couples the negative-eigenvalue sector of a prescribed stabilizer to auxiliary Rydberg states, while engineered dissipation irreversibly transfers the population into the corresponding positive-eigenvalue sector and leaves the target stabilizer manifold dark. This establishes a modular pumping primitive that can be composed to autonomously stabilize general many-body stabilizer manifolds, rather than merely prepare a specific entangled state. The combination of Floquet-selective excitation and fast engineered dissipation accelerates convergence, while transient single-Rydberg excitation and suppressed real multi-Rydberg occupation reduce sensitivity to Rydberg-state loss, blackbody-radiation-induced leakage, and spatial fluctuations. We demonstrate the framework through Bell and multiqubit graph states, including parallel stabilizer pumping that reduces the convergence time for the simulated multiqubit systems. The same dissipative attraction also enables purification of imperfect resource states. These results establish Floquet-engineered stabilizer pumping as a scalable route toward autonomous quantum-state stabilization and protected entanglement generation in neutral-atom platforms.

We explore the applicability of a stochastic time-evolution algorithm based on probabilistic angle interpolation. To simplify the preprocessing of the algorithm, we take the continuous-time limit, thereby explicitly eliminating Trotter errors and streamlining the resource analysis. We also introduce a noise-mitigation method tailored to it. As demonstrations, we apply the algorithm to two representative problems: estimating the ground-state energy of the ${\text{H}}_3^{+}$ molecular Hamiltonian and computing out-of-time-ordered correlators in the sparse Sachdev-Ye-Kitaev model. We evaluate the protocol's performance through numerical simulations and experiments on a trapped-ion quantum computer, Quantinuum Reimei.

The speed of quantum evolution is limited under finite energy resources. While most quantum speed limits (QSLs) are formulated in terms of quantum states, they can be extended to the evolution operator itself and thus impose fundamental limits on how quickly logical gate operations can be implemented on a quantum computer. Here, we derive a general, tight QSL that holds for any unitary evolution under the constraint that the spectral width of the Hamiltonian is bounded. We apply this result to obtain QSLs for several standard quantum gates, including Hadamard, cnot, and Toffoli gates, finding that the QSL can vary significantly across different gates, including ones with the same entangling power. These findings can be understood geometrically using the space curve quantum control formalism, which maps unitary evolution to space curves in Euclidean space. In this formalism, the problem of finding QSLs is recast as the problem of finding minimal-length curves obeying a curvature bound. We find that time-optimal gates map to helices of varying dimensions and that QSLs can be understood from the perspective of a bottleneck principle in which the operator that evolves the slowest governs the minimal gate time.

Antiproton-molecule collisions are of fundamental interest in atomic collision physics and hold direct relevance for radiation biology and hadron therapy. In this work we investigate the single ionization of water, methane, and ammonia molecules by antiproton impact using the continuum-distorted-wave eikonal-initial-state Hartree-Fock approximation. In this model, a numerical Hartree-Fock potential is utilized to describe the interaction between the ejected electron and the target. We present double-differential cross sections for impact energies from 250 to 2000 keV and analyze the angular and energy distributions of ejected electrons. Notably, the results reveal an anticusp in the antiproton-induced spectra at electron velocities close to the projectile velocity, in place of the prominent electron capture to the continuum peak observed for protons. Since no experimental data for differential cross sections are available for antiproton impact, the theoretical results are compared with proton-induced ionization results. We also provide a comparative analysis of the total cross sections against other theoretical methods in the energy range from 10 keV to 10 MeV, finding very good agreement for collision energies above 50 keV.

Within a fully relativistic framework, we discuss the one-loop self-energy correction, generalized to the presence of external blackbody radiation, for a bound electron in the hydrogen molecular ion. The calculations rely on the thermal part of the photon propagator from finite-temperature quantum electrodynamics. The axial dual kinetic balance method, an axially symmetric extension of dual kinetic balance condition to axially symmetric systems, is adopted together with a $B$-spline-based trial function. The results are obtained within the Born-Oppenheimer adiabatic approximation. The thermal shift for the ground-state term of the hydrogen molecular ion is computed as a function of the internuclear distance. Including this correction, we present the resulting shifts of the vibrational levels. The analysis focuses on the dynamical effect, and a comparison is made with data available in the current literature.

Recently, the Kapitza-Dirac (KD) effect has been explored using a pump-probe scheme with ultrafast standing light waves, revealing delay-dependent diffraction fringes in the electron momentum distribution [Lin et al., Science 383, 1467 (2024)]. These fringes have been interpreted as quantum interference patterns arising from stimulated Compton scattering. However, we find that an ensemble of classical trajectories initialized by sampling the electron's initial Wigner distribution can accurately reproduce them, with constructive interference corresponding to the convergence of trajectories in momentum space. This quantum-classical correspondence can be understood in terms of the specific geometry of the evolving quasi-one-dimensional phase-space distribution. As the interaction time increases, increasingly nonlinear electron dynamics deform the phase-space distribution into a complex winding structure, and the classical ensemble captures the subsequent evolution of the diffraction patterns only qualitatively. These findings provide a phase-space interpretation of the origin and temporal evolution of ultrafast KD diffraction fringes and may inform coherent electron beam control and electron microscopy.

We study hard-core dipolar bosons on a square lattice subject to a unidirectional periodic drive that Floquet-engineers anisotropic hopping. Driving along one lattice direction provides a controlled way to suppress transverse tunneling, yielding a kinetically quasi-one-dimensional regime with strongly anisotropic transport within the leading-order high-frequency Floquet effective description. In this limit, the system does not reduce to decoupled chains, because the long-range in-plane dipolar interaction remains isotropic and couples different chains. Focusing on dipoles polarized perpendicular to the plane, for which the interaction is purely repulsive and isotropic, we use sign-problem-free worm-algorithm quantum Monte Carlo simulations to map the half-filling phase diagram versus kinetic anisotropy and dipolar coupling. We find that increasing kinetic anisotropy systematically lowers the interaction strength required to stabilize checkerboard order, demonstrating that Floquet-induced suppression of transverse motion enhances density ordering. Near the superfluid-checkerboard boundary, the concurrent sharp loss of stiffness and growth of checkerboard correlations, their size-dependent sharpening, and the histogram analysis support a weakly first-order transition rounded by finite-size effects. Away from half filling, on the doped sides of the checkerboard plateau, our finite-size data support a narrow checkerboard-supersolid regime with simultaneously finite checkerboard correlations and superfluid stiffness, where the superfluid stiffness is anisotropic but the density pattern is isotropic.

Site selection in chiral optical trapping is often interpreted through the local dipolar force associated with the optical-chirality-density gradient. Whether this rule remains sufficient for a finite particle with appreciable multipolar response is unclear. We combine a focused hybrid-polarized field with a complete multipolar force calculation, a parity-duality decomposition, and two-dimensional fixed-point analysis for a reciprocal chiral sphere. The complete transverse force supports locally stable focal-plane fixed points whose association with the optical-chirality domains depends on particle size and physical multipolar cutoff. The two representative sizes reveal distinct roles of higher multipoles: for one size, the exact finite-size dipolar response already supports a stable state and higher orders modify its local restoring response and position; for the other, higher orders reorganize the stability of roots associated with the two chirality domains. The parity-asymmetric scalar-gradient contribution supplies most of the restoring slope along the representative cut, while the remaining force contributions close the balance and include a local circulating component. The complex Mie responses and their linear and intermultipolar force contributions therefore reorganize transverse trapping-site stability beyond the local optical-chirality-gradient expectation.

Improving multiparameter quantum estimation in magnonic systems via quantum noise suppression is a well-established and critical research objective. In this work, we propose an experimentally realistic scheme to improve the precision of simultaneously estimating different parameters in a cavity-magnon system by utilizing a degenerate optical parametric amplifier (OPA). The OPA enhances the estimation precision by decreasing the most informative quantum Cramér-Rao bound, which is calculated by employing the symmetric logarithmic derivative (SLD) and the right logarithmic derivative. We show that when nonlinearity is introduced into the system, quantum noise is significantly suppressed. Our results show how different physical parameters influence multiparameter estimation precision, and we provide a detailed discussion of the associated physical mechanisms in the steady state. Our results focus on exploring practical Gaussian measurement schemes that can be realized experimentally. In addition, we analyze the system's dynamics, comparing both the SLD quantum Fisher information and the classical Fisher information for both homodyne and heterodyne detection. This approach provides a robust foundation for multiparameter quantum estimation, offering significant potential for application in hybrid magnomechanical and optomechanical systems.

We investigate resonant universal photon blockade in a three-mode four-wave-mixing system. A coherent drive of complex amplitude $F_a$ excites the target mode, while a nondegenerate parametric pump of complex amplitude $E$ generates correlated photons in two auxiliary modes. The target two-photon state is accessed via two competing pathways: sequential coherent excitation and pump-assisted four-wave-mixing conversion of the auxiliary pair with coupling strength $g$. Destructive interference between these pathways leads to a vanishing leading-order two-photon amplitude. At single-photon resonance and zero effective pair detuning, the weak-drive cancellation condition requires $\left|E\right|=[({\kappa }_b+{\kappa }_c)/{\kappa }_a]{\left|F_a\right|}^2/g$ and ${\varphi }_E=2{\varphi }_a+\pi$, reducing to $E=-2F_a^2/g$ for equal decay rates and real $F_a$ and $g$. Master-equation calculations verify antibunching at representative weak-, intermediate-, and strong-coupling points within the below-threshold weak-excitation window. Relative to a representative off-resonant interference node, the resonant scheme yields a larger intracavity one-photon population while retaining strong antibunching. We further quantify the effects of unequal losses, Kerr shifts, static relative-phase mismatch, and the bare auxiliary parametric-oscillation threshold. These results demonstrate a fully bosonic realization of resonant universal photon blockade based on a nondegenerate pair channel.

Raman optical activity (ROA) enables label-free detection of absolute configuration, conformation, and stereochemical structure in chiral biosamples and drug molecules. Since ROA signals are generally small, techniques such as stimulation by a probe beam can be used to enhance signal strength. However, with a classical probe, the measurement precision is still fundamentally limited by its shot noise. To address this limitation, we propose the use of two-mode squeezed vacuum and show that it can achieve sub-shot-noise limited measurement sensitivity. Using quantum estimation theory, we derive the quantum Fisher information and the quantum Cramér–Rao bound (QCRB) for stimulated ROA measurement to quantify the precision enhancement. This improvement comes from photon-number correlations, which suppress the intensity fluctuation common to both modes. We further show that balanced detection of the output intensity difference is a practical measurement scheme that approaches the QCRB and becomes nearly optimal in the small-chirality limit. This opens a promising path toward more sensitive Raman chiroptical spectroscopy of weak and photosensitive samples.

The prequel to this work [Ng et al., Phys. Rev. A 93, 042121 (2016)] proposes the method of spectral photon counting to enhance noise spectroscopy with an optical interferometer. While the predicted enhancement over homodyne detection is promising, the results there are derived by taking an asymptotic limit of infinite observation time; their validity for a finite time remains unclear. To validate the theory, here we perform a numerical study of a finite-time model. Assuming that the signal is an Ornstein-Uhlenbeck process with an unknown variance parameter, we evaluate the Fisher information for homodyne detection, a lower bound on the Fisher information for spectral photon counting, and a quantum upper bound, all without taking the infinite-time limit. To confirm that the Fisher-information quantities are satisfactory precision measures, we also compute the errors of the maximum-likelihood estimator by Monte Carlo simulations. The results demonstrate that the Fisher-information quantities and the estimation errors all smoothly approach their asymptotic limits, and the advantage of spectral photon counting over homodyne detection can remain substantial for finite times.

Any protocol to process quantum information has to conclude with a measurement, aimed at producing a specific set of probabilities of measurement outcomes. In this work we investigate the time, energy, and importantly the genuine quantum resources necessary for transforming a set of measurement probabilities generated by a positive-operator-valued measure to a target set of measurement probabilities. To this end, we first show that the speed of measurement probabilities, defined as the average rate of the surprisal of measurement outcomes, is constrained by the genuine quantum fluctuations contained in the measurement probabilities. Hence, the speed vanishes in the corresponding classical limit. Interestingly, this quantum speed limit can act as a witness for bipartite quantum correlations by selecting an optimal local projective measurement. Furthermore, we obtain a minimum time to transform an initial measurement probability to a target measurement probability and apply this result to analyzing the cost of generating a local athermality in terms of genuine quantum uncertainty.

We formulate coherence-induced hybrid control (CIHC) for mixed-state inverse engineering in driven open quantum systems. The method uses the known dependence of dissipation on coherent driving as a constraint on inverse design. The same fields must produce a prescribed Lewis-Riesenfeld (LR) basis path and the population flow along a target mixed-state trajectory. For a system coupled to a structured bosonic environment, we derive an effective master equation through a reaction-coordinate mapping and a polaron-type projection. The LR-frame transition rates depend on the complete coherent controls and cannot be adjusted independently. We combine shortcuts to adiabaticity endpoint conditions with the mixed-state constraint. We then construct a fixed-basis longitudinal protocol from detailed balance, without fitting an independent equilibrium polarization or dissipative rate. We test its closure, independent forward evolution, grid convergence, and secular conditions along the trajectory. This example illustrates the CIHC constraint within a restricted setting and shows how structured environmental coupling can provide a microscopic implementation.