We propose and analyze nonreciprocal and topology-inspired ground-state cooling in a spinning cavity optomechanical resonator. An exact coupled-mode treatment yields a cross-interference damping rate which shows the increasing rotation suppresses the backscattering-mediated heating pathway, recovering the scattering-free limit. In the degenerate regime, the linearized dynamics admit a Su-Schrieffer-Heeger representation in which optical backscattering acts as a next-nearest-neighbor coupling. This perturbation breaks chiral symmetry and precludes a quantized winding number yet under open boundaries supports an edge-localized Tamm-Shockley-type bound state. With suitable parameters, the boundary channel enables robust phonon extraction and achieves subunity phonon occupancies in the presence of finite backscattering, albeit with a slower cooling rate and a higher steady-state phonon number due to scattering and hybridization.

When two valley edge states (VESs) in an A-B-A structure approach each other, mutual interference inevitably arises. However, in most cases, the degree of interference at a given frequency remains fixed, lacking an effective strategy for continuous tuning of the coupling strength. In this article, we present a coupled topological waveguide in which one channel incorporates the phase-change material ${\mathrm{Sb}}_2{\mathrm{S}}_3$. By adjusting the refractive index of ${\mathrm{Sb}}_2{\mathrm{S}}_3$, the wave vector of the corresponding VES can be flexibly tuned. Since mode coupling is governed by the wave-vector matching condition, this tunability allows precise control of the coupling coefficient between the two VESs at a specific frequency, thereby enabling dynamically reconfigurable beam-splitting behavior. Furthermore, with a large wave-vector mismatch, we achieve fully decoupled transmission, where the VESs propagate along their respective channels with minimal crosstalk, even in closely spaced waveguides. This capability for controllable interference and low-crosstalk propagation provides a promising route for the realization of high-density, multichannel photonic integration.

We theoretically investigate the photon blockade effect induced by quantum interference in a single two-level atom-cavity quantum electrodynamics (QED) system induced by degenerate parametric amplification. Analytical calculations identify the optimal parametric gain and phase settings required to achieve the most favorable conditions for unconventional photon blockade (UPB). Under these optimal parameters, numerical evaluations of the second-order correlation function confirm strong photon antibunching, in agreement with the analytical predictions. Our findings demonstrate that coherent driving of either the cavity or the atom, combined with parametric amplification of the cavity, can yield pronounced photon antibunching when the system is appropriately tuned. Furthermore, we demonstrate that in the cavity-driven configuration, a nonzero cavity-atom coupling strength degrades the UPB effect for the resonant cavity-atom interaction scenario. In contrast, the atom-driven configuration benefits from such coupling, resulting in enhanced photon antibunching under optimal conditions. This work contributes to the development of strongly antibunched single-photon sources, which are essential for advancing quantum technologies.

We model the generation of multiple photon pairs (biphotons) through engineering of two coexisting nearly resonant spontaneous four-wave-mixing (SFWM) processes in five-level atoms driven to a quasi-dark state trapping regime. This is achieved through a suitable choice of two pump beams and one coupling beam whose spectral profiles are taken into account both to provide realistic estimates for the effects of their linewidths on atomic populations, coherences, and photon correlations and to engineer the joint spectral amplitude (JSA) distributions of generated biphotons directly by tuning the beams' parameters. We specifically leverage this tunability to control the degree of spectral indistinguishability of two biphotons with ultranarrow linewidths. The large degree of indistinguishability achievable in our model can be harnessed for advanced applications in quantum communication and information processing and potentially adapted to compatible solid-state interfaces.

Non-Hermitian effects and reentrant localization have attracted significant attention due to their unique physical properties and potential applications. Despite recent experimental advancements, achieving precise control and gaining a deeper theoretical understanding of these phenomena remain challenging. Here, we propose a one-dimensional doubly coupled lattice model, where two sublattices are interconnected via both horizontal and vertical hoppings, to investigate non-Hermitian phase transitions and localization behavior. Asymmetric hopping drives a transition from the Hermitian to the non-Hermitian regime, leading to the emergence of complex energy spectra. Moreover, when a quasiperiodic potential is introduced, the system exhibits a range of localization phases, including extended, localized, and intermediate phases characterized by mobility edges. Notably, under strong quasiperiodic modulation, we observe reentrant localization, where the system undergoes a nonmonotonic transition from localization to delocalization and back to localization as system parameters are varied. Our findings bridge theoretical insight into non-Hermitian phase transitions and localization with a practical circuit-based platform, enabling direct experimental exploration in quantum simulators.

We introduce a resource monotone, the completeness stability, to quantify the quality of quantum measurements within a resource-theoretic framework. By viewing a quantum measurement as a frame, the minimum eigenvalue of a frame operator emerges as a significant monotone. It captures bounds on estimation errors and the numerical stability of inverting the frame operator to calculate the optimal dual for state reconstruction. Maximizing this monotone identifies a well-characterized class of quantum measurements forming weighted complex projective 2-designs, which includes well-known examples such as SIC-POVMs. Our results provide a principled framework for comparing and optimizing quantum measurements for practical applications.

We classify quantum gates according to their capability to generate genuine multipartite entanglement (GME), using a hierarchy based on multipartite separable states. In particular, when a fixed unitary operator acts on the set of $k$-separable states, the maximal (average) genuine multipartite entanglement content produced via that particular unitary operator is determined after maximizing over the set of $k$-separable input states. We identify unitary operators that are beneficial for generating high GME when the input states are entangled in some bipartition, although the picture can also be reversed where such initial entanglement offers no advantage. We investigate the maximum entangling power of a broad range of unitary operators, encompassing special classes of quantum gates, as well as diagonal, permutation, and Haar uniformly generated unitaries by computing the generalized geometric measure (GGM) as the GME quantifier. Additionally, we observe a notable distinction in entangling power based on the nature of the input states: when maximization is restricted to separable states with real coefficients, the entangling power is lower than when the optimization is carried out over arbitrary separable states with complex coefficients, thereby highlighting the role of complex amplitudes in entanglement creation. Furthermore, we determine which unitary operators, along with their corresponding optimal inputs, yield output states with the highest achievable GGM.

Simultaneous quantum-classical communication (SQCC) protocols offer a practical approach to continuous-variable quantum key distribution (CV-QKD) by encoding quantum and classical signals onto the same optical pulse. However, like most QKD protocols, their performance is limited when experimental parameters, such as modulation variance, are optimized based on stationary channel assumptions. In fluctuating environments, such as free-space links, this can result in suboptimal key rates and reduced transmission distances. In this work, we introduce Gaussian postselection into the SQCC framework, enabling a software-based optimization of the modulation variance after channel estimation. This passive approach enhances key rates in both asymptotic and finite-size regimes without requiring hardware modifications and remains effective even when receiver imperfections are taken into account. We demonstrate that our protocol improves the transmission distance and robustness of SQCC relative to the standard fixed-variance SQCC protocol, and approaches the performance of a fully preoptimized system across both fiber and free-space channels. In particular, we show that the protocol enables full communication windows under ideal weather conditions and maintains higher duty cycles during adverse weather in satellite-to-ground scenarios. These results highlight the practicality of postselection-based SQCC for real-world quantum communication over both terrestrial fiber networks and satellite-based free-space links.

One of the most persistent problems in quantum mechanics has been collisional breakup in a few-body system involving two attractive centres. In particular, with the advent of cold target recoil ion momentum spectroscopy, high-precision kinematically complete experimental measurements for such few-body problems became possible. Experimentally measured multidimensional momentum distributions of electrons ionized in intermediate-energy proton collisions with helium are calculated. Experimental and theoretical data of the wave-packet convergent close-coupling method are in excellent agreement, leading to the conclusion that theory has reached a level where it can accurately solve the proton-helium ionization problem in a kinematically complete fashion.

We report a microwave spectroscopy measurement of the muonium $2S_{1/2}\text{−}2P_{3/2}$ fine-structure transition, yielding a transition frequency of $9871.0\pm 7.0\mathrm{MHz}$, in agreement with state-of-the-art QED predictions within one standard deviation. In combination with the recent Lamb shift result, the $2P_{1/2}\text{−}2P_{3/2}$ splitting is determined, improving the spectroscopic characterization of the $n=2$ manifold in muonium. These results provide a stringent test of bound-state QED in a purely leptonic system and establish a path toward future searches for Lorentz violation and muon-specific new physics.

Photoelectron angular distributions (PADs) are sensitive probes of light-matter interactions beyond the dipole approximation. Using first-principles calculations, we present a complete spatial characterization of the PADs for the argon $3s$ and $3p$ subshells. Our theoretical framework systematically incorporates electric dipole ($E1$), quadrupole ($E2$), magnetic dipole ($M1$), and higher-order multipole contributions for arbitrary light polarization. The results reveal striking nondipole effects, specifically, a pronounced forward-backward asymmetry and a strong dependence on the polarization state of the incident light. Although PADs of both subshells show energy-dependent behavior across the soft x-ray regime (400 to 4000 eV), the $3p$ PADs demonstrate significantly greater variation, with nondipole contributions becoming dominant above $1000\mathrm{eV}$. These results establish argon as a fundamental benchmark for advancing photoionization theory and provide critical guidance for experiments at modern light sources, bridging the gap between theoretical predictions and experimental observables.

We study the on-resonance spin-1/2 double-kicked rotor, a periodically driven quantum system that hosts topological phases. Motivated by experimental constraints, we analyze the effects of open and periodic boundary conditions in contrast to the idealized case of infinite momentum space. As a bulk probe for topological invariants, we focus on the mean chiral displacement (MCD) and show that it exhibits a pronounced sensitivity to boundary conditions, which can be traced to the dynamics in momentum space. Under open boundaries, states that would otherwise extend freely become localized at the edges of the finite momentum space, forming quasienergy edge states. While the bulk response measured by the MCD is strongly affected once the evolving wave packet reaches the boundaries, the persistence of these edge states still reflects the bulk-edge correspondence and provides reliable signatures of topological transitions.

We investigate the ground-state phases and spin-scissors dynamics of binary Bose-Einstein condensates confined in a twisted two-dimensional harmonic trap. The ground state hosts three distinct phases (phase-separated, polarized, and phase-mixed) determined by the Rabi coupling, interaction ratio $G$ (between intercomponent and intracomponent interactions), and spin-twisting, which induces edge-localized polarization through position-dependent detuning. In the phase-mixed regime, the ground state is characterized by a finite spin-scissors susceptibility and can be accurately described using local density approximation. In the dynamics, the system exhibits stable periodic beating in the phase-mixed state for $G\le 1$. For $G>1$, its evolution progresses from beat damping (phase-separated state) to polarized relaxation (polarized state), finally reaching stable periodic beating (phase-mixed state) after a finite waiting time. The dependence of the waiting time contrasts sharply with the monotonic behavior of one-dimensional spin-dipole dynamics, revealing qualitatively distinct mechanisms governed by geometry and interactions. In summary, these results establish a unified link between ground-state properties and nonequilibrium responses in twisted spinor condensates, offering a versatile platform for exploring spin-related quantum many-body phenomena.

Recent experiments have realized ultracold gases in twisted-bilayer optical lattices. We show that interacting bosons in these lattices present a highly nontrivial ground-state physics resulting from the interplay between inter- and intralayer hopping and interactions. This physics is crucially determined by site clusterization, which we properly take into account by developing a specifically tailored cluster Gutzwiller approach. Clusterization results in a large variety of different Mott-like phases characterized by typically different occupations of the clusters, and in the appearance of pockets of sites in between which particles can freely move, but which remain for any practical purposes disconnected from the rest of the sites. This peculiar phase, which resembles the well-known Bose glass phase, may occur even for commensurate twist angles and is further enhanced when the twisting is incommensurate. Moreover, in the incommensurate case, the formation of mobility islands may occur even without interlayer hopping solely due to interlayer interactions.

Double-resonance matching of fundamental and second-harmonic frequencies offers a powerful strategy to enhance second-harmonic generation (SHG). However, existing strategies often emphasize frequency alignment while overlooking the critical spatial overlap of the resonance field distributions, which is typically only partial. In this study, we proposed a new SHG enhancement mechanism leveraging ultrastrong coupling (USC) between plasmonic whispering-gallery and cavity modes in a spherical dielectric-metal core-shell four-layer nanostructure. This USC-based design enables simultaneous frequency matching via giant Rabi energy splitting and perfect spatial field overlap, facilitated by near-field interactions in the strong-coupling regime. These features lead to a three to four orders of magnitude enhancement of SHG efficiency across a broad spectral range (0.832–1.525 eV) compared with a standalone dielectric core under identical conditions. Our findings underscore the transformative potential of USC for advancing nonlinear optical processes and offer a robust framework for designing high-efficiency and compact nonlinear optical devices.

We investigate entanglement sharing in a two-qubit sequential measurement scenario using three complementary classical correlation metrics: mutual information ($\mathcal{I}$), a sum of conditional probabilities ($\mathcal{S}$), and the Pearson correlation coefficient ($\mathcal{C}$). By investigating both weak measurement and probabilistic projective measurement (PPM) strategies in unilateral and bilateral scenarios, the phenomenon of entanglement sharing is conclusively certified when multiple pairs of classical correlation metrics simultaneously exceed their thresholds. Our investigation reveals that weak measurement strategies are more favorable than PPM for exhibiting entanglement sharing, regardless of the scenario. Furthermore, the mutual information criterion fails to characterize entanglement sharing in the bilateral scenario, while the Pearson correlation criterion ($\mathcal{C}$) is proven to be the most robust across all strategies and scenarios. These findings unveil a critical tradeoff between measurement disturbance and complementary correlation recovery, which is essential for quantum resource reuse problems.