Recent research in two-dimensional topological matter has generalized the notion of edge states from chiral to antichiral configurations with the same propagating direction at parallel edges, revealing a rich variety of robust transport phenomena. Here we propose that antichiral hinge states can emerge in a three-dimensional higher-order topological insulator or semimetal, where two surface or bulk Dirac points are connected by the hinge states. The band dispersion can be controlled and tilted independently for each hinge using properly designed tunnelings, resulting in tunable antichiral hinge states with programmable propagation direction and velocity. Moreover, we propose experimental realization schemes based on a one-dimensional coupled cavity array with additional synthetic dimensions represented by the photonic orbital angular momentum and frequency. We introduce both longitudinal and transversal electro-optic modulators to generate the desired tunable tunnelings along the synthetic dimensions, which significantly reduce the experimental complexity by eliminating the need for beam splittings and auxiliary cavities. The tunable antichiral hinge states are confirmed by the photonic transmission spectra. Our work presents robust and tunable antichiral hinge-state transports, which pave the way for exploring novel topological matter and their device applications.

We present a general framework to model spontaneous emission in integrated photonic structures by exploiting quantization of the electromagnetic field in terms of asymptotic-in/out modes. This approach allows for an efficient and physically meaningful calculation of the emission rate into each radiative channel of an arbitrary structure, without relying on approximations such as Lorentzian lineshapes or point-like system-bath coupling. We show that with this approach one can recover well-known results for dipole emission in waveguides or ring resonators, and that such results can be easily extended to include the effect of backscattering. Finally, as an application, we design a tunable integrated single-photon source that enables full control over both the emission rate and output mode. This flexibility makes our method particularly well suited for the design and analysis of integrated single-photon sources in various material platforms.

Open quantum systems are ubiquitous in nature and central to quantum technologies. A common description of their dynamics is given by the celebrated Lindblad master equation, which can be generalized to the non-Markovian scenario. In this work, we introduce the non-Markovian ensemble propagation (NMEP) method, which extends the Monte Carlo wave-function (MCWF) method to the non-Markovian case in a simple and general manner. We demonstrate its accuracy and effectiveness in a selection of examples, and compare the results with either analytic expressions or direct numerical integration of the master equation.

Higher-order exceptional points (EPs) in non-Hermitian systems showcase diverse physical phenomena but require more parameter space freedom or symmetries. We report the observation of a third-order exceptional surface and line in a Jaynes-Cummings triangle. A fine-tuning artificial magnetic field enriches the emergence of the third-order exceptional lines (ELs), which require only three tuning parameters when protected by parity-time (PT) symmetry. Third-order ELs maintain robust enhanced sensitivity through a cube-root response mechanism, displaying a greater sensitivity than second-order EPs. We develop a nontrivial fidelity metric based on the biorthogonal associated-state approach that reliably detects EPs while eliminating the unphysical fidelity values in previous approaches. Furthermore, our method captures quench dynamics across EPs, revealing distinct behavior in both PT-symmetric and PT-broken regimes. Our work establishes a platform for studying higher-order geometry in light-matter interactions using circuit QED.

We investigate quantum synchronization in coupled self-sustained oscillators interacting via bosonic exchange. Using a phase-distribution-based synchronization measure, we identify bistable phase locking between 0 and $\pi$ and uncover an expanded Arnold-tongue structure under finite detuning, indicative of enhanced quantum phase locking. Power spectral analysis reveals dual-frequency locking associated with dressed-state formation, a uniquely quantum effect. This spectral splitting persists even without detuning and increases with coupling strength, signaling coherent hybridization of oscillator modes. A comparison with a classical approximation highlights key differences, including the absence of spectral doublets in the classical regime. Finally, we show that increasing nonlinear damping induces a sharp transition in the preferred phase difference and leads to decoherence through spectral peak broadening, underscoring the critical role of dissipation in shaping quantum synchronization dynamics.

There have been many instances where the maximally entangled state as a probe acts better than the product and the nonmaximally entangled states in the task of distinguishing quantum channels. We provide a proof that for the single-shot discrimination of two unitary channels, entangled and product states are operationally equivalent. However, we identify pairs of unitaries that are perfectly distinguishable using a nonmaximally entangled state, but not with a maximally entangled one. This contrast becomes more pronounced when the number of unitaries exceeds two. In every $\text{dimension}⩾3$, we show that there exists a class of unitaries that is indistinguishable under maximally entangled probes, yet perfectly distinguishable using product or nonmaximally entangled inputs. Another interesting set of unitaries in every $\text{dimension}⩾3$ has been presented where only a nonmaximally entangled state acts as a successful probe, while product states and maximally entangled states cannot.

We investigate the dependence of the ionization probability of ${\mathrm{N}}_2$ in an intense laser field on the angle between the laser polarization direction and the molecular axis by recording the yield of ${\mathrm{N}}_2^{+}$ as a function of both the time delay between the pump and probe laser pulses and the polarization angle $\left(\mathrm{\Theta }\right)$ between the pump and probe laser polarization directions when the rotational wave packet of ${\mathrm{N}}_2$ is created by the pump pulse and ${\mathrm{N}}_2$ is ionized by the probe pulse. The Fourier transform of the delay dependence of the ${\mathrm{N}}_2^{+}$ yield exhibits peaks at the energy differences of the rotational levels of ${\mathrm{N}}_2$ with $J+2$ and $J$, with $J$ being the rotational quantum number of ${\mathrm{N}}_2$, and the polarization dependences of the amplitudes of these peaks are mainly given by the Legendre polynomial $P_2(cos\mathrm{\Theta })$. From the comparison with the analytical formula of the polarization dependent Fourier transform spectra, we partly determine the angular dependence of the ionization probability of ${\mathrm{N}}_2$ without estimating the molecular axis distribution of ${\mathrm{N}}_2$ prepared as the ensemble of the rotational wave packets. The resultant angular dependence of the ionization probability suggests the ionization induced by the photoelectron emission from the lower-lying $1{\pi }_{\mathrm{u}}$ orbital of ${\mathrm{N}}_2$ in addition to the highest occupied $3{\sigma }_{\mathrm{g}}$ orbital.

We study the fully itinerant dynamics of ultracold but nondegenerate polar molecules with a spin-$1/2$ degree of freedom encoded into two of their electric field dressed rotational states. Center-of-mass molecular motion is constrained to two dimensions via tight confinement with a one-dimensional optical lattice, but remains mostly unconstrained within the plane. The pseudospins can become entangled through ultracold dipolar collisions, for which the locality of interactions is greatly relaxed by free molecular motion. At the level of single-molecule observables, collision-induced entanglement manifests as spin decoherence, for which our theoretical calculations serve well to describe recent Ramsey contrast measurements of quasi-two-dimensional confined KRb molecules at JILA [A. Carroll et al., Science 388, 6745 (2025)]. In presenting a more detailed theoretical analysis of the KRb experiment, we highlight a key finding that molecular loss enhanced by particle exchange symmetry can lead to a suppression of collective spin decoherence, a mechanism we refer to as “loss-induced quantum autoselection.” We then show that, by utilizing bialkali species with sufficiently large dipole moments, loss can be near completely suppressed in all collision channels via electric field tunable confinement-induced collisional shielding. The afforded collisional stability permits fully coherent spin mixing dynamics, natively realizing unitary circuit dynamics with random all-to-all connectivity and U(1) charge conservation. This work establishes a bridge between the domains of ultracold molecular collisions and many-body spin physics, ultimately proposing the use of nondegenerate bulk molecular gases as a controllable platform for nonequilibrium explorations of itinerant quantum matter.

Quantum Bose-Bose mixtures with large interspecies attraction can form self-bound, liquid-like droplets stabilized by quantum fluctuations. Despite equilibrium densities much lower than those of classical liquids, these droplets exhibit finite surface tension and liquid-like behaviors. Recent experiments have demonstrated Rayleigh-Plateau instability (a paradigmatic example of capillary instability) in elongated droplets confined in an optical waveguide. Here, we consider the case of an infinite filament and extend the theoretical description to include transverse harmonic confinement. By solving the Bogoliubov–de Gennes equations within a single-component framework, benchmarked against full Gross-Pitaevskii simulations, we show that increasing confinement progressively suppresses the instability, leading to complete stabilization beyond a critical trap frequency.

We propose and numerically simulate an all-optical Toffoli (controlled-controlled-not) gate based on the scattering of spatial solitons by asymmetric Pöschl-Teller potential wells. In our scheme, the logical state of the target bit is encoded in the relative spatial ordering of two distinguishable soliton components, while the control bits are represented by the presence or absence of external potential wells. We solve the nonlinear Schrödinger equations governing the soliton dynamics and systematically scan soliton amplitude and velocity, analyzing reflection and transmission coefficients to identify the operational conditions for Toffoli gate behavior. Our results demonstrate that introducing asymmetry in the potential wells significantly broadens the operational parameter window compared to symmetric configurations. We also investigate the impacts of varying degrees of asymmetry and soliton amplitude on gate performance. Furthermore, we examine the influence of weak intercomponent coupling and confirm that it is not essential for gate operation. These findings generalize earlier soliton-based cnot simulations and support the broader feasibility of classical analog modeling of multiqubit logic gates in nonlinear optical systems.

We theoretically discuss a kind of photonic spin-Hall effect (PSHE) for optical beams propagating inside an inhomogeneously twisted anisotropic material. The rotation angle plays the role of an effective gauge field. When the twisting distribution is odd symmetric, the optical beams move along mirror-symmetric trajectories according to their helicity. Connection of this volumetric PSHE with the geometric phase and the Kapitza effect is elucidated.

We analyze the interplay between mechanical and radiation pressure in an optomechanical cavity system. Our study is based on an analytical evaluation of the infinite Bessel summations involved, which previously had led to a numerical exploration of the so-called attractor diagram. The analytical expressions are then suitable for further asymptotic analysis in opposing regimes of the amplitude, which allows for a characterization of the diagram in terms of elementary functions. Building on this framework, we investigate the emergence and properties of optomechanical limit cycles beyond the constraints of the resolved sideband approximation. By employing a Fokker-Planck formalism originally developed in the context of laser theory and then used in cavity optomechanics, we describe the quantum regime of these limit cycles, offering a more detailed and unified analytical perspective.

In this article, we explore the beam dynamics within symmetrically chirped nonlinear waveguide arrays, focusing on linear and quadratic chirping schemes. We propose a practical structure for these arrays that enhances control over light propagation. By employing a continuous approximation of the discrete nonlinear Schrödinger equation, we utilize a semianalytical variational method to analyze beam behavior under waveguide chirping. Our findings indicate that the symmetrically chirped waveguide arrays behave similarly to graded index systems, with varying coupling coefficients analogous to the refractive index in continuous media. We derive a steady-state solution and validate it against numerical simulations, alongside conducting a linear stability analysis to assess the robustness of these solutions. The results reveal that input Gaussian beams in such waveguide arrays follow an oscillatory trajectory akin to that in parabolic index media. Notably, under nonlinear conditions, these beams evolve as discrete solitons. Our rigorous investigation of the propagation characteristics in both linear and nonlinear regimes highlights the intricate dynamics of optical beams within the engineered chirped waveguide arrays, supported by comparisons to comprehensive numerical simulations.

Wave transport in disordered media is a fundamental problem with direct implications in condensed matter, materials science, optics, atomic physics, and even biology. The majority of these studies focuses on disorder-induced localization in Hermitian systems. However, recent studies of non-Hermitian disordered media have revealed unique behaviors, with a universal principle emerging that links the eigenvalue spectrum of the disordered Hamiltonian and its statistics with its transport properties. In this work we show that the situation can be very different in driven-dissipative lattices of cavities, where a uniform gain applied equally to all the components of the system can act as a knob for controlling the wave transport properties without altering the eigenvalue statistics of the underlying Hamiltonian. Our results provide deeper insight into the transport properties of disordered media and will aid in the development of new devices. Our work, which is presented in the context of optics, generalizes to any physical platforms where gain can be implemented. These include acoustics, electronics, and coupled quantum oscillators such as atoms, diamond centers, and superconducting qubits.

We introduce Zernike polynomials as a novel degree of freedom for encoding quantum information in the spatial structure of photons. Building on their orthogonality and completeness over the unit disk, we develop a framework for generating, manipulating, and detecting photons in Zernike modes, and propose methods for realizing single-photon and two-photon Zernike wave packets. We demonstrate analytically that two-photon states generated via spontaneous parametric down-conversion exhibit mode entanglement in the Zernike basis, with correlations arising from selection rules enforced by Clebsch-Gordan coefficients. Our results open a new pathway for structured spatial entanglement, complementary to schemes based on Laguerre-Gaussian or Hermite-Gaussian modes, and suggest practical experimental implementations based on holographic modulation and optical Fourier techniques.

The processing of quantum information is limited by fundamental physical constraints on how information can be encoded, transmitted, and extracted. In particular, the nonorthogonality of quantum states limits their distinguishability, and thermodynamic constraints, including the energetic cost of state preparation and quantum operations, further restrict the viability of realistic information protocols. This work explores the impact of such constraints on the preparation, evolution, and readout of quantum information. We demonstrate that preparing the system for encoding and measurement affects the distinguishability and purity of the resulting ensemble of states. Furthermore, we analyze a noisy communication channel and propose an optimal protocol for encoding and decoding the transmitted information. For this realistic protocol, we show that the maximum probability of successfully retrieving the information is equal to the maximum correlation that can be achieved between the system and the register. The protocol uses only Gibbs states as free resources, ensuring minimal thermodynamic cost. Based on this, we provide a thermodynamic interpretation of the Holevo information, which quantifies the capacity of the transmitted information and establishes a fundamental limit on its retrieval in thermodynamically constrained scenarios.

Recently, experimental measurements of the Larmor time of incident wave packets have been conducted, once again drawing attention to such a time. These experiments measured the tunneling time of Bose-condensed ${}^{87}\mathrm{Rb}$ atoms, with theoretical analyses employing free particles. In this paper, we investigate the tunneling process of wave packets, which, unlike free particles with a definite incident energy, have a continuous distribution of energies. We show how the Larmor time ${\tau }_{z\left(y\right)}$ for a wave packet tunneling through a barrier depends on the barrier width $d$, the barrier's characteristic wave vector $k_0$, the incident wave packet's central wave vector $k_c$, and its width $\sigma$ in wave-number space. When the barrier width $d$ is small, we find that ${\tau }_{z\left(y\right)}$ varies monotonically. For wide barriers ($d>2.0\pi$), we find an anomaly where wave packets with lower incident energy or higher barriers have shorter tunneling times, which is consistent with recent experimental results. Additionally, for narrow wave packets in wave-number space ($\sigma <\gamma$), where $\gamma$ is the width of the fitted Fano peak, the results are generally consistent with those for plane waves. However, as the wave packet widens in wave-number space, the maximum points of ${\tau }_{z\left(y\right)}$ will undergo a nonlinear decrease and $\sigma$ significantly affects the maximum Larmor time.

We introduce a class of thermal operations based on the collision model, where the system sequentially interacts with uncorrelated bath molecules via energy-preserving unitaries. To ensure finite complexity, each molecule is constrained to be no larger than the system. We identify a necessary condition for cooling below the bath temperature via a single collision: The system must initially lack a well-defined effective temperature, even a negative one. By constructing an iterative protocol, we demonstrate that sub-bath cooling is achievable without a machine under these restricted thermal operations. Moreover, introducing a qubit machine further enhances both the cooling limit and energy efficiency. These findings contribute to the broader study of cooling with finite resources.