Superheterodyne Rydberg atomic receivers (RARs) combine high sensitivity, a broad operational frequency range, and phase- and frequency-resolved detection capabilities, making them promising candidates for next-generation radio-frequency receivers. Currently, the widespread deployment of RARs is limited by narrow instantaneous bandwidth. We use time-dependent perturbation theory to derive the linear approximate solution to the master equation. Floquet theory is employed to evaluate the total harmonic distortion arising from a single-tone excitation, enabling the characterization of the signal amplitude range over which the linear approximation remains valid. Transforming this linear solution into the Laplace domain yields an expression for the frequency response of the Rydberg atomic electro-optical conversion system. Furthermore, by vectorizing the superoperators and the density operator, we recast the original superoperator differential equation as a linear system of equations, enabling efficient numerical calculation. We numerically simulate the amplitude-frequency and phase-frequency response spectra, where the amplitude-frequency response reflects the gain across different frequencies. This enables analysis of how laser and local-oscillator parameters affect gain and bandwidth. Indeed, the gain metric based on the slope of the steady-state response curve coincides exactly with the zero-intermediate-frequency gain in the amplitude-frequency response. We employ the particle-swarm optimization algorithm to optimize the channel capacity of RARs under the constraints of photon shot noise and thermal-electrical noise. This algorithm demonstrates rapid convergence, efficiently identifying optimal laser and local-oscillator parameters. This study is expected to provide valuable insights for improving the sensitivity and bandwidth of superheterodyne RARs.

We explore the operation of quantum batteries in the Lipkin-Meshkov-Glick (LMG) model, when they are charged either through a sudden quench in the magnetic field strength or by coupling them to a single-mode bosonic charger. Through initializing the battery in either the symmetric or broken-symmetry phase of the LMG model, we analyze how the different spectral properties can affect the performance of both the charging and discharging of the battery. In particular, we show that by quenching the magnetic field strength from the symmetric phase to the broken-symmetry phase, we can achieve a significant enhancement in stored energy, as well as stable and efficient ergotropy extraction. Similar observations can be made when introducing weak coupling between the battery and the bosonic charger, while the amount of stored work and ergotropy saturate at strong coupling. These findings emphasize the importance of the magnetic field dynamics or environmental coupling in optimizing charging performance, which could lead to practical applications in quantum energy storage.

Bosonic Gaussian thermal states form a fundamental class of states in quantum information science. This paper explores the information geometry of these states, focusing on characterizing the distance between two nearby states and the geometry induced by a parametrization in terms of their mean vectors and Hamiltonian matrices. In particular, for the family of bosonic Gaussian thermal states, we derive expressions for their Fisher-Bures, Kubo-Mori, and $\alpha \text{−}z$ information matrices with respect to their mean vectors and Hamiltonian matrices. An important application of our formulas consists of fundamental limits on how well one can estimate these parameters. We additionally establish formulas for the derivatives and the symmetric logarithmic derivatives of bosonic Gaussian thermal states. The former could have applications in gradient descent algorithms for quantum machine learning when using bosonic Gaussian thermal states as an ansatz, and the latter could have applications in formulating optimal strategies for single-parameter estimation of bosonic Gaussian thermal states. Finally, the expressions for the aforementioned information matrices could have additional applications in natural gradient descent algorithms when using bosonic Gaussian thermal states as an ansatz.

The vectorial nature of light-matter interaction is crucial for nanophotonic processes. However, a key requirement for experimental vectorial analysis—the controllable excitation and detection of different polarization components—remains challenging, especially in near-field optics, where the optical fields exhibit strong subwavelength spatial variations. Here the interaction of three orthogonal polarization components, represented by the three lowest-order surface plasmon polariton (SPP) modes of a silver nanowire (AgNW), with an edge of discontinuous refractive index is investigated. Selective excitation and collection of specific SPP modes via a fiber taper-AgNW hybrid probe reveals distinct modulations for different modes/polarization components. Reflection signals for two excitation modes exhibit subwavelength profiles, where the fundamental mode excitation realizes superresolution edge imaging. In transmission measurements, the far-field radiation patterns of all three modes are significantly modulated by the edge. We developed the local reflection and transmission models to quantitatively analyze these results, which show excellent agreement with both experimental measurements and numerical simulations. Our work not only provides insights into the nanoscale vectorial light-matter interactions but also establishes a platform with potential applications in areas such as near-field modulation, biosensing, optical communication, and superresolution optical edge imaging.

Analog coprocessors are presently intensively developing with the aim to optimize energy computations of neural networks. In this work we focus on the possibility of using detection of collective oscillations in optical systems for computational purposes. We show that in a system of coupled resonators the collective oscillations can be used to implement matrix-vector multiplication. The matrix is formed by the coupling constants between the resonators, and the input vector is formed by the initial occupancies of the involved modes. The frequency of the collective oscillations is growing with the number of the involved modes, similarly to Rabi oscillations. The time needed for their detection, i.e., averaging, decreases with an increase in the input vector dimension.

Starting with heuristic assumptions about locality and causality, Bell established a numerical upper bound on statistical correlations between spatially separated systems and showed that quantum systems could violate it. This upper bound, also known as the Bell or Clauser-Horne-Shimony-Holt (CHSH) inequality, can be derived from an experimental setup known as the CHSH game. Tsirelson used the CHSH formulation to derive a higher, maximal bound on quantum correlations. Later, Popescu and Rohrlich (PR) studied correlations beyond quantum theory that were constrained only by the no-signaling principle, a condition that disallows superluminal communication between observers. They showed that such correlations could theoretically violate the Tsirelson bound. Is there some conceptually simple or transparent principle that explains the large gap between the Tsirelson bound and the PR bound? Or do we have to appeal to the technical axiomatic structure of quantum theory? In this paper, we reformulate the CHSH game in terms of indivisible stochastic processes. Using Barandes's stochastic-quantum correspondence and its associated definition of causal locality, we present a proof of the Tsirelson bound. In particular, we show that, unlike the no-signaling principle alone, the postulates defining causally local, indivisible stochastic processes are precisely strong enough to allow for violations of the Bell inequality up to, but not beyond, the Tsirelson bound.

We investigate the dynamics of two identical spinless fermions on a one-dimensional lattice with open boundary conditions (OBCs), subject to quasiperiodic long-range interactions. Using numerical exact diagonalization (ED), we study this nonintegrable system as a continuous-time quantum walk and uncover a robust correlated dynamical regime. This regime, characterized by an approximately constant interparticle distance, emerges under sufficiently strong quasiperiodic modulation of the long-range interactions. Further, the study shows that the behavior is determined by the nature of the interaction and the choice of boundary condition. Notably, by tuning the phase of the quasiperiodic modulation, we observe three distinct manifestations of this phenomenon: localization, nearest-neighbor separation oscillations, and next-nearest-neighbor separation transitions, each arising for specific initial separations. Furthermore, we identify the suppression of entanglement entropy in the system, including instances of oscillatory behavior. Our results highlight how quasiperiodic long-range interactions shape few-body quantum dynamics.

Classical simulations of noisy quantum circuits are instrumental to our understanding of the behavior of real-world quantum systems and the identification of regimes where one expects quantum advantage. In this work, we present a highly parallelizable tensor-network-based classical algorithm, equipped with rigorous accuracy guarantees, for simulating $n$-qubit quantum circuits with arbitrary single-qubit noise. Our algorithm represents the state of a noisy quantum system by a particular ensemble of matrix product states from which we stochastically sample. Each pure state evolved under a single-qubit noise process is then represented by the ensemble of states that achieves the minimal average entanglement (the entanglement of formation) between the noisy qubit and the remainder. This approach lets us use a more compact representation of the quantum state for a given accuracy requirement and noise level. For a given maximum bond dimension $\chi$ and circuit, our algorithm comes with an upper bound on the simulation error, runs in $\mathrm{poly}(n,\chi )$-time, and improves upon related prior work (1) in scope by extending analytic methods from the three commonly considered noise models to general single-qubit noise, (2) in performance by deriving an exact, closed-form solution to the local entanglement minimization problem, previously approached via variational heuristics, thereby guaranteeing local optimality without numerical optimization overhead, and (3) in conceptual contribution by showing that the fixed unraveling used in prior work becomes equivalent to our choice of unraveling in the special case of depolarizing, dephasing, and amplitude damping noise acting on a maximally entangled state.

The entanglement entropy (EE) of any bipartition of a pure state can be approximately expressed as a sum of entanglement links (ELs). In this work, we introduce their exact extension, i.e., the entanglement hyperlinks (EHLs), a type of generalized mutual information defined through the inclusion-exclusion principle, each of which captures contributions to the multipartite entanglement that are not reducible to lower-order terms. We show that any EHL crossing a factorized partition must vanish, and that the EHLs between any set of blocks can be expressed as a sum of all the EHLs that join all of them. This last result allows us to provide an exact representation of the EE of any block of a pure state, from the sum of the EHLs which cross its boundary. To illustrate their rich structure, we discuss some explicit numerical examples using ground states of local Hamiltonians. The EHLs thus provide a remarkable tool to characterize multipartite entanglement in quantum information theory and quantum many-body physics.

We investigate the mechanisms of energy transfer and distribution in quantum batteries composed of multiple two-level battery cells within the single-excitation subspace. By employing the continuous-time quantum walk, we analyze how energy and ergotropy evolve dynamically under three representative topology structures, including the chain, the ring, and the complete graph. Two different coupling methods are examined separately, with the charger uniformly coupling all battery cells and the charger only locally coupling with a single battery cell. The results show that the topology structure and coupling symmetry crucially determine both the spatial distribution and transfer efficiency of energy. In the chain, energy propagates directionally with distinct interference fringes. In the ring, complete translational symmetry leads to bidirectional propagation without boundary reflection. In the complete graph, the system reduces to a low-dimensional collective model without spatial phase variation, so energy does not propagate between sites. When the coupling strength decays exponentially with distance, due to the introduction of high-order coupling and multipath interference, it exhibits richer dynamic behavior. In addition, the average power collective dynamics and scaling relationship under uniform coupling are analyzed.

Network quantum steering characterizes the correlations among parties in a quantum network with different levels of trust. It is closely related to the distribution of trusted and untrusted parties, and can be detected by the violation of some steering inequalities. However, different methods of constructing inequality criteria result in varying degrees of capability to detect network steering using these inequalities. In this paper, we construct a class of network steering inequality criteria based on the distribution characteristics of network sources. They have been validated as superior to the existing network steering inequality criteria in Werner states or $X$ states. More importantly, they are applicable to a general network composed of two-qubit states. The existing network steering inequality criteria are only applicable to certain known fixed network structures.

Grover's algorithm is a fundamental quantum algorithm that achieves a quadratic speedup for unstructured search problems of size $N$. Recent studies have reformulated this task as a maximization problem on the unitary manifold and solved it via linearly convergent Riemannian gradient ascent methods, resulting in a complexity of $\mathcal{O}(\sqrt{N/M}log(1/\varepsilon ))$, where $M$ denotes the number of target items and $\varepsilon$ denotes the success probability error. In this work, we adopt the Riemannian modified Newton (RMN) method to solve the quantum search problem, under the assumption that the ratio $M/N$ is known. We show that, in this setting, the Riemannian Newton direction is collinear with the Riemannian gradient in the sense that the Riemannian gradient is always an eigenvector of the corresponding Riemannian Hessian. This structure removes the overhead of Hessian inversion and allows the proposed RMN method to retain the local quadratic convergence in terms of the error $\varepsilon$. More precisely, we rigorously prove an overall complexity of $\mathcal{O}(\sqrt{N/M}+loglog(1/\varepsilon ))$. Furthermore, our approach remains Grover compatible, namely it relies exclusively on the standard Grover diffusion and oracle operators to ensure algorithmic implementability, and its parameter update process can be efficiently precomputed on classical computers.

Possible signatures in the photoelectron spectrum of nuclear motion during two-photon single ionization of a diatomic molecule by a single ultraviolet pulse are explored using twelve combinations of model potential curves for initial, near-resonant intermediate, and final cationic electronic states at a range of pulse durations and intensities. From these simulations, we find that a key condition for the photoelectron spectrum to display clear evidence of nuclear motion in the resonant intermediate electronic state during a single pulse is that the dynamics in the intermediate state be significantly different from the vibrational dynamics in both the initial neutral state and the final ionic state of the molecule. Additionally, we present and test a computational approach that explicitly propagates wave packets for nuclear motion on the bound and discretized continuum electronic states.

We investigate the quantum computing of the vibrational dynamics of ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ by constructing the vibrational third-order anharmonic Hamiltonian in qubit and qudit form by two types of qubit encodings (binary and direct) and a qudit encoding. We simulate the time-dependent vibrational population transfer using the three different encodings, including the effect of noise, and find that the qudit encoding leads to the most accurate results for both ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ because of the small number of terms in the qudit Hamiltonian as long as the same values of the entangling gate error rates are adopted. Although the entangling gate errors of current qudit quantum computers are approximately one order of magnitude larger than the entangling gate errors of current qubit quantum computers, our results suggest that the simulation of vibrational dynamics is a promising application for future qudit quantum computers.

We study the magnetic-field dependence of the interactions between two alkaline-earth(-like) Rydberg atoms, $\mathrm{Sr}$ and $\mathrm{Yb}$. Considering the pair of Rydberg states $|ns,S_1,m_J\rangle$ and $|(n+1)s,S_1,m_J\rangle$, we show that the effective Hamiltonian takes the form of an XXZ-type quantum spin model, as in the alkali-atom case [M. Kunimi and T. Tomita, Phys. Rev. A 112, L051301 (2025)]. We find that the behavior of the anisotropy parameter for $\mathrm{Yb}$ at zero magnetic field is significantly different from that for other atomic species. This behavior arises from the interplay of strong spin-orbit coupling and the resulting multichannel redistribution of Förster defects in $\mathrm{Yb}$. We systematically calculate the interaction parameters of the XXZ model in the presence of a magnetic field and show that they can be tuned by the field. As applications to quantum many-body problems, we investigate one-dimensional systems in the large-anisotropy regime and show that the folded XXZ model can be realized in $\mathrm{Yb}$ systems without fine-tuning of the field. We also investigate two-dimensional square-lattice systems and show that a supersolid phase can emerge in the ground state at the mean-field level.

We investigate scattering phenomena in a one-dimensional attractive Bose-Hubbard model with a time-periodically-modulated impurity. We analyze both single-particle and pair (doublon) transmission, exploring a range of interaction strengths and drive amplitudes. Our exact numerical results reveal excellent quantitative agreement with analytical predictions in the high-frequency limit. At intermediate and weak attractive interactions, we observe significant pair dissociation and the emergence of dynamically localized single-particle modes. These features are reminiscent of Floquet bound states in the continuum. These findings provide avenues for engineering controllable quantum transport and localized states in ultracold-atom experiments.

We study a low-density system of “spinful” lattice fermions with on-site attraction of different fermionic species in the presence of site disorder acting oppositely on different species (such as a random Zeeman field on opposite spins). In the weak-intersite-hopping regime, the attraction promotes the formation of composite pairs consisting of fermions of different species occupying the same lattice site, while sufficiently strong anticorrelated disorder tends to disintegrate the pairs. We calculate the probability of formation of such pairs depending on the relation between the interaction and the disorder strengths. We also study the transport properties of the system in the phase of composite pairs influenced by the anticorrelated disorder and show that this influence turns out to be parametrically weaker than in the case of a conventional potential disorder. We calculate the shift of the superfluid transition temperature caused by disorder and obtain the temperature dependence of the pairs' mobility in the range of temperatures exceeding that of degeneracy.