We present a theoretical framework for electromagnetic scattering by particles with a permittivity that is periodically varying in time, based on a perturbative approach. Within this framework, we derive explicit expressions for the scattering matrix of the dynamic system in a first-order Born approximation, relating it directly to the corresponding static problem. We show that inelastic scattering amplitudes are governed by overlap integrals between static modes at the input and output frequencies. Using this insight, we analyze scattering from a time-modulated, isotropic, dielectric sphere and a high-permittivity dielectric cylinder, and demonstrate how modal orthogonality can suppress inelastic channels, while appropriate tuning of geometric parameters can significantly enhance them. In particular, we show that cylindrical resonators support strong inelastic scattering when resonance-to-resonance optical transitions, induced by the temporal variation, involve a high-$Q$ supercavity mode. Comparison with full time-Floquet calculations confirms that the first-order Born approximation remains quantitatively accurate for modest modulation amplitudes and provides clear physical intuition for frequency conversion and resonance-mediated scattering processes in time-modulated photonic resonators.

Mechanical systems provide a unique test bed for studying quantum phenomena at macroscopic length scales. However, realizing quantum states that feature quantum correlations among macroscopic mechanical objects remains an experimental challenge. Here, we propose a quantum system in which two micro-electromechanical oscillators interact through a chain of Rydberg atoms confined in optical tweezers. We demonstrate that the coherent dynamics of the system generate entanglement between the oscillators. Furthermore, we utilize the tunability of the radiative decay of the Rydberg atoms for dissipative entanglement generation. Our results highlight the potential to exploit the flexibility and tunability of Rydberg atom chains to generate nonclassical correlations between distant mechanical oscillators.

Optical frequency combs are utilized in a wide range of optical applications, including atomic clocks, interferometers, and various sensing technologies. They are often generated via four-wave mixing in chip-integrated microring resonators, a method that requires low optical input power due to the high-quality factor of the resonator, making it highly efficient. While the classical properties of optical frequency combs are well established, this work investigates the quantum-mechanical characteristics of the individual comb modes. We derive closed-form analytical expressions describing the squeezing, second-order correlation, and joint spectral intensity between the generated signal and idler modes. This comprehensive theoretical framework enables an intuitive understanding and optimization of the quantum features across the comb, revealing conditions for substantial squeezing and entanglement relevant for quantum information processing. Our findings highlight the profound impact of design and dispersion on these quantum properties and offer a foundational tool for chip-integrated quantum applications, including quantum sensing, computing, and communication.

Radiation-matter hybridization allows atoms to serve as mediators of effective interactions between light modes and, conversely, to interact among themselves via light. Here, we exploit the spatial structure of atomic ensembles to control the coupling between modes of distinct cavities, thereby reshaping the resulting atom-photon spectra. We show that extended homogeneous clouds suppress mode-mode couplings through destructive interference, whereas grated clouds can preserve them under specific Bragg conditions. This leads to mode-mode spectral subsplittings, where collectivity arises not only from the number of atoms but also from the ability to tune modes of different cavities independently. Our results establish spatially engineered atomic ensembles as a pathway to selective photon transfer between modes and precise control of many-body complexity.

Open quantum systems can be approximately described by non-Hermitian Hamiltonians (NHHs) and Liouvillian superoperators. The two approaches differ by quantum jump terms corresponding to a measurement of the system by its environment. We analyze the emergence of exceptional points (EPs) in NHHs and Liouvillian superoperators. In particular, we show how EPs in NHHs relate to a different type of EPs—multiblock EPs—in the no-jump Liouvillian, i.e., the Liouvillian superoperator in absence of quantum jump terms. We further analyze how quantum jump terms modify the multiblock structure. To illustrate our general findings, we present two prime examples: qubits and qutrits coupled to additional ground-state levels that serve as sinks of the population. In those examples, we can navigate through the EP block structure by a variation of physical parameters. We analyze how the dynamics of the population of the states is affected by the order of the EPs. Additionally, we demonstrate that the quantum geometric tensor serves as a sensitive indicator of EPs of different kinds.

Spectator qubits (SQs) for random-telegraph noise mitigation have been proposed by Song et al., [Phys. Rev. A 107, L030601 (2023)], where an SQ operates as a noise probe to estimate optimal noise-correction control on the hard-to-access data qubits. It was shown that a protocol with adaptive measurement on the SQs and a Bayesian estimation-based control can suppress the data qubits' decoherence rate by a large factor with quadratic scaling in the SQ sensitivity. However, the protocol’s practicality in real-world scenarios remained in question, due to various sources of imperfection that could affect the performance. We therefore analyze here the proposed adaptive protocol under nonideal conditions, including parameter uncertainties in the system, efficiency and time delay in readout and reset processes of the SQs, and additional decoherence on the SQs. We also explore analytical methods of Bayesian estimation in the time domain and generalize the map-based formalism to nonideal scenarios. This allows us to derive imperfection bounds at which the decoherence suppression remains approximately the same as under ideal conditions.

Pure dephasing is the dominant leak mechanism in photonic cat qubits because its phase errors disrupt the parity protection, rendering the qubit vulnerable to energy relaxation. In this paper, we reveal that this dephasing mechanism conceals an interesting physical phenomenon: it induces asymmetric leakage from the cat-state subspace, where even- and odd-parity cat states decay at different rates. This leak asymmetry enables the dynamics of the system to be described by a non-Hermitian Hamiltonian, thereby transforming the cat qubit into a platform with controllable gain and loss for probing non-Hermitian physics. Importantly, we demonstrate that the cat-state manifold provides unique hardware-level protection for non-Hermitian simulation, including the exponential suppression of frequency detuning errors and the capability to distinguish stochastic single-photon loss via real-time parity monitoring. These features enable our protocol to determine the location of exceptional points with significantly higher precision than traditional systems, such as coupled linear resonators, which are susceptible to undesired environmental noise. Within this platform, we demonstrate the possibility to control the parity-time symmetry phase transition in a single cat qubit by adjusting its amplitude. Moreover, we couple two cat qubits to realize an entanglement phase transition induced by the exceptional point. Our work constructs a controllable non-Hermitian system simulator, overturning the conventional paradigm that treats dephasing as harmful noise.

We demonstrate that the ground state of a spin-1 XXZ chain with uniaxial anisotropies, single-ion anisotropy $D$ and Ising-like anisotropy $J$, within the Haldane phase can serve as a resource state for measurement-based quantum computation implementing single-qubit gates. The gate fidelity of both elementary rotation gates and general single-qubit unitary gates composed of rotations about the $x, y$, and $z$ axes is evaluated, and is found to exceed 0.99 when $D$ or $J$ is appropriately tuned. Furthermore, we derive an analytic expression for the rotation-gate fidelity under the assumption that the state lies within the ${\mathbb{Z}}_2\times {\mathbb{Z}}_2$-protected Haldane phase, showing that it is determined by the postmeasurement spin-spin correlation function and the failure probability. The observed enhancement of gate fidelity in the spin-1 XXZ chain originates from the strengthening of antiferromagnetic (AFM) correlations near the AFM phase, which effectively suppresses failure states.

Quantum information theory reveals a clear distinction between local and nonlocal correlations through the entanglement across spatially separated subsystems. The orthogonal complement of an unextendible biseparable basis (UBB) consists entirely of genuine multipartite entangled states, representing the most robust form of such nonlocal correlations. In this paper, we provide a sufficient condition for any subspace to be genuinely entangled, enabling the systematic construction of high-dimensional genuinely entangled subspaces (GESs) from UBBs. Our construction yields the largest known GES ever obtained from a UBB. In fact, every state in this subspace is 1-distillable across every bipartition, which is one of the crucial results we obtained. Furthermore, we prove that every UBB is indistinguishable under LOCC protocols, underscoring a distinct manifestation of quantum nonlocality. The UBBs we construct exhibit strong nonlocality in this scenario, making cryptographic protocols secure not only against LOCC-based attacks but also against coordinated group attacks. We introduce a no-go condition that certifies such an extreme form of nonlocality. All previously known UBBs satisfy this condition, which may lead to the misconception that strong nonlocality is an inherent property of every UBB. However, we construct a UBB that violates the no-go condition and exhibits locality across certain bipartitions, challenging conventional notions of unextendibility and nonlocality in multipartite quantum systems.

Multipartite entanglement serves as a foundational resource for scalable quantum information processing. We propose a tunable scheme for generating multipartite entanglement in non-Hermitian quantum systems by incorporating driven ancillary qubits with adjustable control fields. This non-Hermitian network allows precise regulation of effective coupling strengths among multiple non-Hermitian microwave cavities, enabling the scalable preparation of maximally entangled states on an accelerated timescale. To demonstrate the capability of our approach, we perform numerical simulations based on a system of multiple microwave cavities interfaced through superconducting qubits. The results reveal that non-Hermitian cavities achieve multipartite entanglement generation significantly faster than conventional Hermitian systems. This temporal advantage becomes increasingly substantial as the system approaches an exceptional point (EP) of order $2^n$ at $J=0$ under reduced perturbation. Notably, our scheme maintains strong robustness against systematic errors of the control parameters, intersystem crosstalk, and environmental noise. These features establish the proposed method as a viable and scalable approach for achieving high-fidelity multipartite entanglement near higher-order exceptional points in non-Hermitian quantum networks.

We aim to reduce the cost of the current bosonic randomized benchmarking proposal. To do this, we introduce two filter functions: one uses immanants, the other uses characters of the special unitary group. These filters avoid computing Clebsch-Gordan (CG) coefficients and yield simple variance expressions. The character filter is not only efficient to compute, but also has a constant, low variance. Our filters rely on the same data as the original proposal. We also discuss an example with photon loss and gain. Our numerical evidence shows that a scheme using weak coherent states and intensity measurements can yield estimates close to those obtained without loss or gain. Our work could support simpler platform characterization and streamline data analysis.

We investigate the exact analytic structure of fermionic many-body excited states through a case study of the harmonic problem. By analyzing highly degenerate eigenstates using a group-theoretic approach, we can reconstruct each eigenspace according to the exchange symmetry, isolating a small subset of bosonic and fermionic states from a much larger set of nonsymmetric states. Moreover, we show that the fermionic and bosonic states are in one-to-one correspondence. Furthermore, we demonstrate that the exact fermionic wave functions can be expressed in a factorized form consisting of a bosonic ground-state wave function and an antisymmetrized multivariate polynomial, an algebraic structure which we refer to as the antisymmetrizer. The antisymmetrizer naturally embodies an explicit dependence on interparticle distances, reflecting the two-body interactions in the Hamiltonian. We show that this representation is significantly more efficient than conventional multideterminant expansions, providing valuable insights into the development of approximate yet efficient representations of excited-state wave functions in more realistic chemical systems.

Measurements of the production of $5snd{}^1{D}_2–5s^2{}^1{S}_0$ ultralong-range Rydberg dimers through photoassocation in an ultracold ${}^{84}\mathrm{Sr}$ atomic gas are reported. The molecular potential associated with the Rydberg $D$ state is anisotropic and the molecular states are characterized by the vibrational quantum number $\nu$ and the total angular momentum $\vec{K}=\vec{L}+\vec{N}$, where $\vec{L}$ and $\vec{N}$ are the electronic orbital angular momentum and rotational angular momentum, respectively. The measured molecular binding energies agree reasonably well with theoretical predictions. Additionally, the electron-atom scattering leads to broader line shapes in the photoassociation spectrum than might be expected simply from the angular momentum of the initial colliding cold-atom pairs.

It is widely recognized that finite temperatures degrade quantum coherence and can induce thermalization. Here, we study the effect of finite temperature on a kicked Tonks-Girardeau gas, which is known to exhibit many-body dynamical localization and delocalization under periodic and quasiperiodic kicks, respectively. We find that many-body dynamical localization persists at finite—and even high—temperatures, although the coherence of the localized state is further degraded. In particular, we demonstrate a modified effective thermalization of the localized state by considering the initial temperature. Moreover, we show a many-body dynamical localization transition at intermediate temperature. Our work extends the study of many-body dynamical localization and delocalization to the finite-temperature regime, providing guidance for cold-atom experiments, particularly in the strongly interacting regime.

Superoscillation is a phenomenon whereby localized oscillations in a band-limited function can oscillate locally at a rate faster than its highest spatial frequency, providing a promising route to far-field linear superresolution imaging. However, most existing superoscillatory microscopes depend on complex masks consisting of hundreds of rings, which present challenges in fabrication and parameter optimization. In this work, we demonstrate a superresolution microscope that employs a confocal fluorescence configuration, utilizing two-ring structured illumination for a small pinhole and three-ring structured illumination for a large pinhole. By introducing the metrics of effective resolution and energy efficiency, we establish polarization selection guidelines for different numerical apertures and systematically examine the relationship between these two metrics. Moreover, by extending the few-ring modulation concept to a Fresnel zone plate design, we develop a modified Fresnel zone plate that achieves higher energy efficiency than a conventional microscope objective without sacrificing resolution. This work provides a practical strategy for constructing high-performance superoscillatory optical systems with simplified architectures.

We study the noisy dynamics of periodically driven, discrete-step quantum walks in a one-dimensional photonic lattice. We find that in the bulk, temporal noise that is constant within a Floquet period leads to decoherence-free momentum subspaces, whereas fully random noise destroys coherence in a few time steps. When considering topological edge states, we observe decoherence no matter the type of temporal noise. To explain these results, we derive a nonperturbative master equation to describe the system's dynamics. We experimentally confirm our findings in a time multiplexed photonic lattice implemented in a double-fiber ring setup subject to laser pulse input states, in which we engineer different types of temporal noise.

The introduction of nonlinearities into lattices with topological band structures has led to the discovery of various types of solitons. The Su-Schrieffer-Heeger (SSH) lattice, as the most fundamental topological model, has been extended into the nonlinear regime. In particular, nonlinear edge states and bulk solitons exhibiting intensity humps against a zero background have been extensively studied in nonlinear SSH lattices. In this paper, we systematically investigate dark solitons in nonlinear SSH lattices. These dark solitons maintain a nonzero and constant background, featuring intensity dips either in the bulk of the lattice or at its edges, and residing spectrally in the semi-infinite gap or the middle finite gap. Regardless of the specific type of dark soliton, the intensity dip remains well preserved and is not affected by the band structure of the original linear lattice. Although the dark solitons we have identified are generally dynamically unstable across a broad range of parameters, several types exhibit linear stability when the intracell coupling is much larger than the intercell coupling. Our findings may provide valuable insights for the exploration of novel types of solitons in nonlinear topological lattices.

Here we present an approach to superradiance in dense atomic samples in the presence of dipole-dipole interactions. We have considered all-to-all interactions as a first step toward understanding the more complicated position-dependent interactions. In addition, we combine the Holstein-Primakoff and mean-field approximations, from which we derive master equations for both the strong- and weak-coupling regimes between the sample and the reservoir. We find that, in both cases, the emitted radiation exhibits striking features, with characteristic emission times much shorter and intensities much higher than those of Dicke superradiance. In particular, in the strong sample-reservoir coupling regime, a comb of superpulses emerges within an envelope whose characteristic emission time is significantly reduced and whose intensity is substantially enhanced relative to Dicke superradiance.

In this paper, we propose a robust protocol for achieving precise parity measurements of $N$ cat-state qubits stabilized in $N$ Kerr nonlinear cavities, leveraging the steady states of an auxiliary cavity mode. The interactions between the cat-state qubits and the auxiliary cavity are mediated by a superconducting artificial atom. By modulating the classical field applied to the artificial atom at suitable frequencies, we derive a parity-dependent effective Hamiltonian for the system. When the artificial atom is coupled to a thermal reservoir, a relatively strong energy relaxation is induced. Under the dissipative dynamics governed by the effective Hamiltonian, this relaxation drives the auxiliary cavity mode toward two distinct steady states corresponding to the parities of the $N$ cat-state qubits. As a result, the parity information of the cat-state qubits can be extracted through the measurement of the auxiliary cavity. Numerical simulations indicate that the protocol is robust to systematic calibration errors (in the drives' Rabi frequencies and coupling strengths), cavity photon loss, and ancilla energy relaxation within realistic parameter regimes. Rather than relying on population transfers, the protocol reads out parity by mapping the global parity to distinct auxiliary-cavity steady states, providing an alternative route to parity measurements of many cat-state qubits.