We investigate temporal scattering in lossless Drude media and reveal an overlooked role of the zero-frequency flatband associated with static polarization charge. This flatband forms an exceptional line spanning all wave numbers and can be directly excited during temporal scattering at photonic time interfaces, generating nonpropagating static fields alongside the usual reflected and transmitted waves. Eigenvector coalescence at the corresponding exceptional points leads to two distinctive features absent in previously studied systems: a static mode whose amplitude increases linearly with time and an additional static component arising from the system's generalized eigenvector. Remarkably, these effects occur without violating total energy conservation, underscoring the Hermitian nature of the dynamics. Our findings present an alternative physical picture of temporal scattering, sharply distinct from that in dispersionless and Lorentz-dispersive media.

We study an adiabatic topological passage of two Su-Schrieffer-Heeger (SSH) chains mediated by a nonlocal atom. When two finite SSH chains are in the topological phase and the frequency of the atom is equal to the center frequency of the SSH chains, the system is reduced to a subsystem that describes the coupling of a nonlocal atom to the edge states of two SSH chains. In this case, we can find dark states that act as adiabatic topological passages. This allows us to adiabatically transfer excitations of the atom to either end of two SSH chains in a fully controllable way. In addition, we show good robustness of the adiabatic topological passages to both atom frequency mismatch and the coupling disorders in the two SSH chains. Our study provides a method to realize quantum information processing and fabricate quantum optical devices based on the coupling of nonlocal atom to topological matter.

Bound entanglement refers to entangled states that cannot be distilled into maximally entangled states and therefore cannot directly be used in many quantum information processing protocols. We identify a relationship between bound entanglement and the Markov gap, which is introduced within holography via the entanglement wedge cross section and is related to the fidelity of the partial Markov recovery problem. We prove that a bound entangled state must have a nonzero Markov gap. Conversely, for sufficiently large systems, a state with a weakly nonzero Markov gap typically has a bound entangled or separable marginal state, where entanglement is undistillable. Furthermore, this implies that the transition from a bound entangled to a separable state originates from the properties of states with a weakly nonzero Markov gap, which may be dual to nonperturbative effects from a holographic perspective. Our results shed light on the investigation of the Markov gap and enhance interdisciplinary applications of quantum information.

Nonstabilizerness is a resource for quantum computing that has been extensively studied in qudit networks. It describes the degree to which Clifford gates cannot generate a given state, capturing the advantage of quantum over classical computing. However, its definition in continuous variables and general composite systems remains an open issue. We study the magic resource in a bipartite system, the asymmetric quantum Rabi model, a paradigmatic model from quantum optics. We explore the presence of nonstabilizerness in the qubit-reduced system throughout the Hamiltonian parameter space, the role of light-matter interactions in its generation, and the manifestation of Wigner function negativity in the corresponding bosonic degree of freedom. Finally, we discuss our results for magic state preparation in the strong and ultrastrong-coupling regimes within the context of quantum informational systems.

Quantum error correction is essential for reliable quantum computation, where surface codes demonstrate high fault-tolerant thresholds and hardware efficiency. However, noise in single-shot measurements limits logical readout fidelity, forming a critical bottleneck for fault-tolerant quantum computation. We propose a dynamic measurement scheduling protocol that suppresses logical readout errors by adaptively redistributing measurement tasks on data qubits from error-prone to stable nodes. The protocol balances gate errors and measurement noise while ensuring compatibility with the error correction cycle by operating after the stabilizer measurements are complete, using shallow entangled circuits. When addressing realistic scenarios where temporal constraints are governed by decoherence limits and error-correction requirements, we implement reinforcement learning to achieve adaptive measurement scheduling. Numerical simulations show that logical error rates can be reduced by up to 34.98% for code distances ranging from 3 to 11, with enhanced robustness in measurement-noise-dominated systems. Our protocol offers a versatile, hardware-efficient solution for high-fidelity quantum error correction, advancing large-scale quantum computing.

Measurement-based quantum computation is a quantum computing paradigm that employs single-qubit measurements performed on an entangled resource state in the form of a cluster state. A basic ingredient in the construction of the resource state is the type-II fusion procedure, which probabilistically merges two separate photonic cluster states by a quantum measurement. We generalize the type-II fusion procedure by generalizing the measurement setup, and classify the resulting final states, which also include cluster states up to single-qubit rotations. We prove that the probability for the success of the generalized type-II fusion is bounded by fifty percent and classify all the possibilities to saturate the bound. We analyze the enhancement of the fusion success probability above the fifty percent bound by the reduction of the entanglement entropy of the resulting state. We prove that the only states that can be obtained with a hundred percent probability of success are product states.

The study of unique entangled states has recently garnered much attention for characterizing unconventional condensed matter phases and phase transitions beyond the Landau symmetry-breaking paradigm. In this work, we propose to investigate a fracton model through periodically modulating the four-body ring-exchange interactions. We study the entanglement structure of the ground state and uncover that the engineered model exhibits long-range entanglement at the critical point, characterized by the conditional mutual information and central charge of conformal field theory. The anomalous transport properties of the fracton model with quench dynamics demonstrate the Hilbert-space fragmentation and restricted mobility of the fracton excitations. Additionally, we extend the model to a square lattice under open boundary conditions to showcase the presence of a symmetry-protected corner state, a distributed Greenberger-Horne-Zeilinger state. Our work provides a promising way to study fracton models with Floquet engineering in state-of-the-art quantum simulation experiments and opens new possibilities for exploring diverse and uncharted quantum phases in these systems.

Mid-circuit measurement and reset of subsets of qubits are crucial ingredients of quantum error correction and many quantum information applications. Measurement of atomic qubits is accomplished through resonant fluorescence, which typically disturbs neighboring atoms due to photon scattering. We propose and prototype a scheme for measurement and reset that provides both spatial and spectral isolation by using tightly focused laser beams and narrow atomic transitions. The unique advantage of this scheme is that all operations are applied exclusively to the read-out qubit, with little overhead and negligible disturbance to the other qubits of the same species. In this paper, we pave the way for noninvasive and high-fidelity mid-circuit measurement and demonstrate all key building blocks on a single trapped barium ion.

The simplest, algebraic quantum-electrodynamical corrections due to the double-negative energy subspace and instantaneous interactions are computed to the no-pair energy of two-spin-1/2-fermion systems. Numerical results are reported for two-electron atoms with a clamped nucleus and positronium-like genuine two-particle systems. The Bethe-Salpeter equation provides the theoretical framework, and numerical methods have been developed for its equal-time time slice. In practice, it requires solving a 16-component eigenvalue equation with a two-particle Dirac Hamiltonian, including the appropriate interaction. The double-pair corrections can either be included in the interaction part of the eigenvalue equation or treated as a perturbation to the no-pair Hamiltonian. The numerical results have an $\alpha$ fine-structure constant dependence that is in excellent agreement with the known ${\alpha }^3{E}_{\mathrm{h}}$-order double-pair correction of nonrelativistic quantum electrodynamics.

We study the formation of transient Faraday patterns and spin textures in driven quasi-one-dimensional and quasi-two-dimensional spin-1 Bose-Einstein condensates under the periodic modulation of $s$-wave scattering lengths $a_0$ and $a_2$, starting from the antiferromagnetic phase. This phase is characterized by a Bogoliubov spectrum consisting of three modes: One mode is gapped, while the other two are gapless. When $a_0$ is modulated and half of the modulation frequency lies below the gapped mode, density and spin Faraday patterns emerge. In that case, in quasi-one-dimension, the spin texture is characterized by periodic domains of opposite $z$ polarizations. When driven above the gap, the spin texture is characterized by random orientations of spin vectors along the condensate axis. Qualitatively new features appear in the driven quasi-two-dimensional condensate. For instance, when driven above the gap, the spin textures are characterized by anomalous vortices and antivortices that do not exhibit phase winding in individual magnetic components. Below the gap, the spin texture exhibits irregular ferromagnetic patches with opposite polarizations. The spatial spin-spin correlations in quasi-one-dimension exhibit a Gaussian envelope, whereas they possess a Bessel function dependence in quasi-two-dimensions. Under the $a_2$ modulation, the density patterns dominate irrespective of the driving frequency, unless the spin-dependent interaction strength is sufficiently lower than that of the spin-independent interaction. The intriguing scenario of competing instabilities can emerge when both scattering lengths are simultaneously modulated. Finally, we show that the competing instabilities result in a complex relationship between the population transfer and the strength of the quadratic Zeeman field while keeping all other parameters constant.

We explore instabilities in binary superfluids with a nonvanishing relative superflow, particularly focusing on counterflow and coflow instabilities. We extend recent results on the thermodynamic origin of finite superflow instabilities in single-component superfluids to binary systems and derive a criterion for the onset of instability through a hydrodynamic analysis, which applies to interacting many-body systems at finite temperature. We find that the onset of these instabilities is signaled by the determinant of the Hessian of the thermal free energy diverging and changing sign. We verify this hydrodynamic prediction in a holographic binary superfluid modeled with gauge-gravity duality, which naturally incorporates strong coupling, finite temperature, and dissipation. We also compare to results obtained using the Gross-Pitaevskii equation for weakly interacting Bose-Einstein condensates and find that the same criterion continues to apply at zero temperature, where it reduces to evaluating derivatives of the supercurrents with respect to the superfluid velocities. We observe that the critical velocities of these instabilities follow a general scaling law related to the interaction strength between superfluid components. Finally, the nonlinear stages of the instabilities are studied by full time evolution using gauge-gravity duality, where vortex annihilation leads to a decrease of superfluid velocity back to a value where the binary superfluid phase is stable.

The four-boson universality suggests the existence of the second excited tetramer state in a system of cold ${}^4\mathrm{He}$ atoms. It is not bound but could be seen as a resonance in the atom-trimer scattering. This process is rigorously calculated using the momentum-space transition operator framework with two realistic interatomic potentials. The $S$-wave phase shift and cross section show a resonant behavior below the excited trimer threshold, but there are sizable nonresonant contributions from $P$ and $D$ waves as well. The position and width of the resonant state is determined, and for the latter significant finite-range effects are found.

The Gross-Pitaevskii equation is widely used for vortex dynamics, but finite domains with hard walls or confining potentials distort bulk behavior through vortex-image effects or induced flows. Periodic boundaries reduce wall artifacts yet cannot realize finite net vorticity because of topological obstruction, so bulk simulations with nonzero circulation are typically unavailable. Hence, we impose quasi-periodic boundary conditions that keep the superfluid's density periodic while enforcing phase windings consistent with a net prescribed total vorticity. This setting conserves the net number of vortices and enables long-time tracking of vortex trajectories in settings that finite containers cannot capture. This allows us to study vortex depinning and nucleation leading to the creation of Kármán vortex streets and perfectly periodic vortex arrays. The framework also provides a toy model for studying vortex dynamics in the bulk of neutron stars, free of possible limitations induced by confining potentials.

We numerically investigate the formation of axially modulated plasma strings through the filamentation of two interfering femtosecond Bessel beams. The constituent Bessel beams have different central spot sizes and propagate collinearly. Our results show that filamentation of these beams in air leads to the formation of intense axially modulated light filaments, and corrugated plasma strings with high modulation depths and tunable modulation periods. We find that the modulation periods of the intensity and the plasma density are identical and comparable to the modulation period of the intensity in the linear propagation regime. Furthermore, we show that, in the nonlinear propagation regime, the modulation period is independent of the pulse energy and can be tuned by selecting appropriate central spot sizes for the interfering Bessel beams. Finally, we propose a simple interferometric arrangement using a single axicon to generate two interfering Bessel beams with adjustable spot sizes enabling the creation of axially modulated plasma strings with tunable periodicity at high input powers.

In quantum mechanics, observables correspond to Hermitian operators, and the spectra are restricted to be real. However, the dynamics of the underlying fields may allow complex eigenvalues and therefore create the possibility of braiding structures. Here we study the braiding of dynamical eigenvalues in quantum systems by considering Hermitian bosonic Kitaev chains with multiple bands. The dynamics of the quantum fields in these systems are described by their dynamical matrices, which have complex eigenvalues. We show that there are symmetry constraints imposed on these dynamical eigenvalues. Despite these constraints, braiding is possible for frequencies within the effective gain and loss regions of the complex plane. We explicitly construct two- and three-strand braidings using the exceptional points found in the system and discuss possible implementations.

We theoretically investigate quantum-enhanced coherent anti-Stokes Raman scattering (CARS) using squeezed light to amplify vibrational transition rates at low photon flux. Quantum sensing approaches are needed for nondestructive nanometrology such as in bioimaging where reduced photodamage is desired while retaining resolution and sensitivity. We analyze both single-mode squeezing applied to the pump field and two-mode squeezing between the pump and Stokes fields. We also show that the ordering of displacement and squeezing operations—whether displacement precedes squeezing or squeezing precedes displacement—has an impact on the resulting CARS transition amplitudes due to a difference in the photon number and the quantum-enhancement coefficients, with the latter offering a stronger enhancement in the case of two modes squeezing of the pump and Stokes under experimentally accessible conditions. Our calculations capture these quantum enhancements through the intrinsic photon-number correlations of squeezed light, eliminating the need for interferometric detection or higher pump powers that are otherwise required to reach comparable sensitivities in classical CARS. Finally, we outline a quantum plasmonic extension of our model in which local field enhancements caused by surface plasmon excitation in metallic nanoparticles can be incorporated via mode-selective field amplification factors, offering a pathway toward combining squeezed-light quantum optics with surface-enhanced nanoscale spectroscopy and imaging.

Helium atoms in the $1s50s{}^{3}S_1$ Rydberg level have been resonantly coupled to the $2\pi \times 11.722\mathrm{GHz}$ second harmonic mode of a chip-based superconducting coplanar wave-guide microwave resonator. To achieve this, the single-photon electric-dipole-allowed $1s50s{}^{3}S_1$ $\to$ $1s50p{}^{3}P_J$ transition was tuned into resonance with the resonator mode through the ac Stark shift induced by a second strong $2\pi \times 3.350\mathrm{GHz}$ microwave dressing field. The effects of this dressing field, and residual uncanceled dc electric fields at the location of the atoms close to the superconducting chip surface were interpreted with support from Floquet calculations of the energy level structure of the Rydberg states. To observe appreciable population transfer in the $1\mu \mathrm{s}$ atom-resonator interaction time using this transition, which had an electric dipole moment of $1500e{a}_0$, pulsed microwave fields were injected into the resonator. From the photon occupation number in the resonator mode under these conditions, the single-photon Rabi frequency associated with the coupling of the atoms to the resonator was estimated to be $\sim 2\pi \times 100\mathrm{Hz}$. These results represent an important step toward operation of this Rydberg-atom–superconducting-circuit interface in the single-photon strong-coupling regime.

We analyze several implementations of all-optical single-photon transistors (SPTs) operating in the continuous-wave (cw) regime, as presented in the companion paper [Phys. Rev. A 113, L011701 (2026)]. The devices rely on ensembles of Rydberg atoms interacting via van der Waals interactions. Under electromagnetically induced transparency (EIT), a weak probe field is fully transmitted through the atomic ensemble in the absence of control photons. Exciting a collective Rydberg state with a single control photon breaks the EIT condition, thereby strongly suppressing the probe transmission. We show how collective Rydberg interactions in an atomic ensemble, confined either in an optical cavity or in free space, give rise to two distinct probe-induced dephasing mechanisms. These processes localize the control excitations, extend their lifetimes, and increase the device efficiency. We characterize the SPTs in terms of control-photon absorption probability and probe gain, supported by numerical simulations of realistic one- and three-dimensional ensembles. The proposed cw devices complement previously demonstrated SPTs and broaden the toolbox of quantum light manipulation circuitry.