The Aharonov-Bohm (AB) effect remains a cornerstone of fundamental and applied physics. In this work, we utilize the AB caging effect originated from an effective magnetic field induced by multiorbital interactions, creating an all flat band (FB) lattice system. Normally, FB states are known for being compact in space and having a zero tail; therefore, their mobility in a linear environment is generally understood as impossible. We propose a Floquet driving protocol in an all-FB photonic system to fully control the dynamics of localized photonic states. The modulation of the Hamiltonian along the propagation coordinate allows the translation of compact states in the direction of constructive interference, resulting in an effective stroboscopic quantum walk-like effect. We find that the traveling states exist in chiral pairs. We experimentally implement the Floquet driven protocol using femtosecond laser written photonic waveguides and demonstrate directional control of the propagation, determined by the relative phase of the input condition.

The secondary rainbow, a classic fold caustic, presents a long-standing challenge in wave theory because standard semiclassical approximations predict unphysical intensity nulls near the Brewster angle. We resolve this Brewster-caustic confluence by developing a uniform asymptotic theory that integrates complex angular momentum theory with the Chester-Friedman-Ursell expansion. By incorporating first-order amplitude gradients, our framework regularizes these polarization-dependent caustics, effectively decoupling the macroscopic caustic envelope from high-frequency Mie diffraction. Validated for relative refractive indexes $1.18<N<2$, this size-parameter-independent $O\left(1\right)$ computational framework bridges classical meteorological optics with modern singular optics, providing a robust analytical foundation for polarimetric inverse scattering.

We revisit quantum $\varphi$-synchronization in a dissipatively coupled cavity-magnon system and formulate the calculation within one consistent system-bath model. A Hermitian photon-magnon interaction of strength $g$ is supplemented by a common Markov channel $L_c=\sqrt{2\mathrm{\Gamma }}(a-im)$. Interference between coherent and dissipative coupling produces the asymmetric rates ${\lambda }_1=g-\mathrm{\Gamma }$ and ${\lambda }_2=g+\mathrm{\Gamma }$, while the same channel necessarily supplies correlated input noise. We derive the quantum Langevin equations from the input-output model and show explicitly that the reduced adjoint Lindblad map is not an operator-algebra homomorphism; canonical commutators are instead preserved by the full Langevin dynamics, including the input fields. For the linear Gaussian system, a quantum Itô product calculation gives the closed second-moment equation $\dot{V}=AV+V{A}^{\mathsf{T}}+D$, with a nondiagonal diffusion matrix fixed by the common bath. This construction answers how the higher-order moments are obtained without raising a first-moment solution to a power. At resonance the drift spectrum has an exceptional point at ${\mathrm{\Gamma }}_{\mathrm{EP}}=\sqrt{g^2-{(\kappa -\gamma )}^2/4}$. For $g/\kappa =2$, $\gamma /\kappa =0.1$, a vacuum common bath, and a magnon-bath occupation $n_m=10$, the fluctuation measure $S_q^{\varphi }$ increases from 0.256 at $\mathrm{\Gamma }=0$ to 0.672 at the exceptional point; the full measure, which also retains the mean-amplitude mismatch, increases from 0.243 to 0.632. A thermal-bath control shows that this improvement is caused by reservoir engineering rather than by spectral coalescence alone. The exceptional point is therefore an experimentally identifiable spectral marker of the strong-dissipation regime, not an independent source of noiseless topological enhancement.

We investigate enantiodetection for both a single cyclic three-level chiral molecule and a mixture of a finite number of chiral molecules by monitoring the steady-state intracavity photon number in a cavity-QED platform. Our scheme exploits the intrinsic global $\pi$-phase difference between opposite enantiomers to engineer destructive or constructive interference pathways, enabling a direct readout of enantiomeric excess with an error below $5\%$ and exhibiting robustness against energy-level dissipation. To capture mesoscopic many-molecule effects beyond mean field while avoiding brute-force master-equation simulations, we employ a generalized discrete truncated Wigner approximation, which is well suited for systems with many yet a finite number of molecules. These results pave the way for implementing enantiodetection in realistic quantum-optical settings.

Nonreciprocal transport at the few-photon level is important for integrated quantum optics and quantum information processing. Unlike conventional small atoms, giant atoms interact with a waveguide through multiple discrete coupling points, allowing photons to accumulate phases along different coupling paths. In this paper, we theoretically investigate few-photon diode effects in a one-dimensional waveguide chirally coupled to a dissipative giant atom. By solving the Schrödinger equation, we obtain analytical solutions for both single-photon and two-photon scattering processes. Our results show that the two-point coupling structure of the giant atom allows diode effects to occur in multiple frequency regions, rather than only near resonance. By tuning the distance $L$ between the two coupling points, one can modify the propagation phase and the interference condition. This provides a geometric way to control the operating frequency range of the diode effect. For the chiral coupling configuration considered here, the optimal diode performance is obtained when the atom-waveguide coupling rate $\mathrm{\Gamma }$ and the dissipation rate $\kappa$ satisfy $\mathrm{\Gamma }/\kappa =1$. The two-photon diode effect further shows a clear dependence on $\mathrm{\Gamma }/\kappa$. For $\mathrm{\Gamma }/\kappa \gg 1$, the nonreciprocal response mainly appears in the bound-state-dominated region. In contrast, for $\mathrm{\Gamma }/\kappa \ll 1$, the transport tends to become reciprocal. These results indicate that nonlocal giant-atom coupling, chiral coupling, and dissipation can work together to realize frequency-tunable few-photon nonreciprocal transport.

Vacuum fluctuations of quantum fields provide an unavoidable environment for any quantum system coupled to it. We study the interplay between boundary conditions and acceleration in determining decoherence of a two-level Unruh-DeWitt detector coupled to a scalar field in a cylindrical cavity. We show that the decoherence rate closely follows the emission profile, and exhibits Purcell-like enhancement for both inertial and uniformly accelerated detectors. The acceleration induces an effective smearing of the resonant density of states, diluting the resonance enhancement for large accelerations while replacing the inertial off-resonant decay with an oscillatory behavior for small accelerations. For moderate accelerations, this interplay between cavity-induced and acceleration-assisted effects results in an extended region of cavity parameters where decoherence is strongly suppressed, particularly in regimes where the inertial detector otherwise experience strong decoherence. Thus, contrary to naive expectations, the Unruh thermality in a suitably engineered cavity can enhance rather than degrade quantum coherence, providing a very uncharacteristic feature of quantum fields in noninertial frames.

The theory of dynamical diffraction (DD) in perfect crystals is the backbone of high-precision neutron and x-ray diffraction experiments, enabling accurate determination of crystal-structure factors and the realization of perfect-crystal interferometers. In practice, however, real crystals exhibit deformations and imperfections, including surface roughness, defects, temperature gradients, angled crystal faces, and curvature, that degrade interferometer performance and are difficult to model using conventional DD theory, particularly in complex geometries. To address these challenges, a quantum information (QI) model for DD has been under development, with demonstrated experimental agreement both for ideal crystals and in the presence of some imperfections such as surface roughness and defects. Here, we present a unified quantum walk model that is now suitable for reproducing a broad range of established DD effects. We demonstrate this by incorporating several diverse internal crystal effects influencing DD intensity distributions, including linear temperature gradients, the DD Talbot effect, and angled or miscut crystals. These results establish the QI model as a comprehensive and flexible framework for experimental analysis, as well as for the design of next-generation perfect-crystal neutron interferometers and neutron optical components, such as condensing monochromators.

In phase-randomized weak coherent pulse (WCP) implementations of the quantum key distribution (QKD) BB84 protocol, the decoy method is often used to compensate BB84's vulnerability against photon number splitting attacks. However, this typically introduces extra complexities and requirements on experimental devices. In this paper, we are therefore interested in phase-randomized WCP implementations without the decoy method. We examine the performance of three QKD protocols with different classical announcement structures, namely, BB84, SARG04, and No Public Announcement of Basis (NPAB) BB84, using numerical security proof techniques. Key rates are computed using the openqkd security software [J. Burniston et al., software openqkdsecurity, ver. 2.0.2 (2024)]. We compare secure key rates of the three protocols in asymptotic and finite-size regimes for lossy and noisy channels. The three protocols show different relative advantages depending on the channel behavior. Canonical BB84 shows robustness against errors and depolarization, SARG04 demonstrates resilience against high-loss channels, and NPAB BB84 shows potential advantages against physical misalignment between QKD devices.

Entanglement distillation is the process of converting noisy entangled states into maximally entangled pure states via local operations and classical communication. A long-standing, unresolved question is which entangled states are amenable to distillation, known as the distillability problem. For Bell-diagonal qutrit states with a Weyl structure, combining two existing results shows that violating the positive partial transpose (PPT) criterion is both necessary and sufficient for one-copy distillability. However, these results do not identify a Schmidt-rank-2 witness that maximizes robustness to white noise. To address this limitation, we present a noise-robust entanglement-distillation scheme for all non-PPT Bell-diagonal qutrit states with a Weyl structure. Specifically, we construct a Schmidt-rank-2 eigenvector of the partially transposed density matrix associated with its unique, threefold degenerate negative eigenvalue. This feature makes the derived entanglement distillation protocol resilient to white-noise effects on the quantum states. Our results thus make noisy entangled qutrit pairs more accessible for future quantum technologies.

We investigate the private capacity of quantum channels using the recently proposed quantum convolution theory for discrete-variable quantum systems. We focus on the role played by magic resources in this framework. First, for a broad class of convolutional channels, we find that the private capacity is zero if the fixed environmental state is a stabilizer state. Moreover, we show that the private capacity can be nonzero for some magic environmental states. For pure environmental states, we further prove that the private capacity of a discrete beam-splitter channel is upper bounded by twice the modified relative entropy of magic of the environment. In addition, if the environmental state exhibits a certain symmetric structure, even if it is magic, the corresponding private capacity will also vanish for a class of convolutional channels. Together, these results show that environmental magic is necessary but not sufficient for positive private capacity in the channel class considered here, while also providing a quantitative upper bound on the achievable private rate.

We analyze the WAHUHA Floquet protocol recently applied to arrays of Rydberg atoms and derive beyond-leading-order corrections in the high-frequency expansion of the effective spin theory. We find that an appropriate choice of the pulses times can enforce an approximate symmetry corresponding to the conservation of the total magnetization. The interaction channels emerging from higher-order Floquet terms affect three-body bound states (trimers), which gain a significant mobility. We estimate the corresponding enhancement in one-dimensional spin chains and conclude that their dynamics is within experimental reach. Detrimental effects due to the proliferation of particles outside of the trimer magnetization sector are found to occur and spread on timescales slower than the trimer propagation. We further show that long-range interactions enhance trimer propagation and that two-dimensional triangular geometries can host energetically isolated trimer bands, providing a possible route to reduce resonant mixing with higher-magnetization sectors. Our results establish a concrete route to realizing mobile multiparticle bound states in Floquet-engineered Rydberg platforms.

Ultracold atoms interacting with narrow-linewidth microwave fields enable high-resolution spectroscopy and provide high-field sensitivity, offering a powerful platform for probing quantum nonlinear effects. In this work, we observe microwave Autler-Townes (AT) splitting in a ladder-type five-level Rydberg system. A set of microwave-coupled Rydberg states is accessed via two-photon optical excitation. The tunable microwave field strongly couples the $48D_{5/2}$ and $46F_J$ levels, giving rise to multilevel AT spectra. The AT spectra and corresponding splitting features are characterized by measuring the population in both $46F_J$ fine-structure levels as a function of optical and microwave frequencies as well as the microwave field strength. In addition to the microwave-dressed AT splittings, we observe avoided crossings of the $48D_{5/2}$ with both dressed $46F_J$ fine-structure states, which are in close proximity of each other and are clearly resolved thanks to the narrow linewidth of the microwave spectroscopy. Simulations of the microwave AT spectra and the associated anticrossing behavior show good agreement with the experimental results.

We study the role of retardation in the energy shift of Rydberg states induced by thermal radiation, focusing on the case of temperatures higher than those for which the electric dipole approximation is expected to apply. As anticipated by Farley and Wing [J. W. Farley and W. H. Wing, Phys. Rev. A 23, 2397 (1981)], retardation needs to be taken into account in calculations of this energy shift around and above the temperature $\alpha m{c}^2/\left(3k_{\mathrm{B}}{n}^2\right)$, where $n$ is the principal quantum number of the state considered, $m$ is the mass of the electron, and $k_{\mathrm{B}}$ is the Boltzmann constant, e.g., around and above 1440 K for $n=100$. The corresponding nondipole shift dominates the electric dipole shift at about 2.5 times that characteristic temperature. Thermal shifts arising from retardation and from the electric quadrupole interaction are of the same order of magnitude as the diamagnetic thermal shift and would thus need to be taken into account in the circumstances where the latter is relevant.

Nitrous oxide (${\mathrm{N}}_2\mathrm{O}$) is an important atmospheric molecule whose interaction with charged particles is relevant for radiation-driven processes in environmental and applied sciences. In this work, we investigate the energy and angular distributions of the absolute double differential cross section  for secondary electrons emitted from ${\mathrm{N}}_2\mathrm{O}$ molecules in collisions with 100-keV protons. Measurements are performed for electron energies between 1 and 400 eV and emission angles ranging from 20° to 160°. The experimental results are compared with the theoretical predictions within the continuum distorted wave–eikonal initial state (CDW-EIS) framework. The molecular electronic structure is described at the Hartree-Fock level, and the bound molecular orbitals are represented through a single-center expansion with symmetry-adapted angular functions. The data exhibit good agreement at low electron energies, while deviations grow at higher energies and backward emission angles. By combining precise measurements with detailed theoretical analysis, the present work establishes stringent benchmarks for theory and advances the understanding of electron emission involving environmentally important molecules.

Ultrafast chirped pulses provide a powerful route to controlling coherent dynamics in multilevel atomic systems. In the strong field regime, however, the physical origin of spectral asymmetry is obscured by the combined effects of pulse chirp, timing linkage, and branch dependent couplings. Here we investigate the asymmetric coherent dynamics of fine structure resonances in rubidium driven by chirped femtosecond pulses. By combining femtosecond transient absorption measurements, transient-grating frequency-resolved optical gating (TG-FROG) pulse characterization, and an analytical three level model based on the Magnus expansion, we examine how chirped excitation reshapes the absorption response of the Rb D1 $\left(5p^2{P}_{1/2}\right)$ and D2 $\left(5p^2{P}_{3/2}\right)$ transitions. The measurements show that the observed spectral asymmetry depends not only on the sign of the chirp, but also on the group delay variation imposed by the compressor geometry. The asymmetry persists even after the timing linkage is compensated, which shows that it does not arise solely from the pump probe timing shift. Further analysis indicates that chirp acts mainly by modulating the phases of the relevant quantum pathways. This reshapes pathway interference and governs the asymmetric partition of the excited state population. These results establish an analytical framework for chirp based control of resonant responses in multilevel atomic systems and highlight the role of phase control in ultrafast quantum state manipulation.

We investigate generalized Bloch oscillations of a single doublon defect in a one-dimensional antiferromagnetic $t–J_{\mathrm{z}}$ chain subjected to linear and quadratic magnetic-field gradients. By mapping the spin-charge coupled many-body dynamics onto an effective single-particle model, we reveal how the Néel background mediates parity-dependent coupling between the defect and the external fields. The linear gradient induces a staggered potential that splits the Wannier-Stark ladder into two intertwined subladders, producing a characteristic beating pattern in the center-of-mass motion with a subband offset accurately captured by third-order perturbation theory. The quadratic gradient generates sublattice-dependent tilts that shear the ladder into a scissor-like profile, yielding site-dependent beating periods that encode the nonlocal spatial averaging of the defect wave function. When both gradients coexist, their interplay is fundamentally nonadditive: the quadratic gradient breaks the two-site periodicity that forbids second-order linear responses, unlocking a dominant cross-coupling proportional to $B_{\mathrm{z},1}{B}_{\mathrm{z},2}$. This leaves distinct fingerprints on the Bloch-oscillation spectrum—a rigid baseline shift of the fundamental doublet and asymmetric broadening of the first harmonic. These predictions are quantitatively corroborated by exact many-body simulations of the real-time density evolution and center-of-mass dynamics. Our work establishes a gradient-induced unlocking mechanism for multigradient defect spectroscopy in quantum magnets, offering a framework for probing parity-protected selection rules and their controlled breaking via generalized Bloch oscillations in tunable quantum simulators.

Coherent exciton transport in dye aggregates is degraded by molecular vibrations, resulting in short exciton dephasing times and limited coherent pulse travel distances. However, in the race against decoherence, this travel distance can be extended if conditions are found that permit faster pulse propagation, which, in turn, may facilitate applications in exciton-based quantum information processing. We compute the exciton dispersion relations for several transmission architectures to identify those possessing modes with the greatest group velocity. We find that transmission lines consisting of multiple coupled linear assemblies are capable of exciton propagation velocities that exceed those of a single-line transmission line. The best of these exhibited a maximum group velocity roughly double that of a single-row transmission line with comparable nearest-neighbor dye couplings. As a first effort to focus on what can be achieved under ideal circumstances in short transmission lines, the effects of both environmental fluctuations and static disorder have been neglected.

The effect of a longitudinally periodic group-velocity dispersion (GVD) perturbation on both bright-soliton and platicon comb states is still unclear. We investigate a dual-coupled Kerr microresonator in which GVD varies periodically along the propagation direction while its average is unchanged. The periodic GVD modulates the phase mismatch of opposite sidebands, and the linearized sideband matrix becomes periodic. We use Floquet theory over one modulation period to analyze the modulation instability (MI). In the mixed normal-anomalous $(+/-)$ configuration, the phase-mismatch modulation gives rise to additional MI sidebands at the parametric-resonance condition. Numerical simulations based on the split-step Fourier method show that periodic GVD enhances the breathing of a dissipative Kerr soliton (DKS)–like state. The soliton peak oscillates continuously, and the high-order comb components are redistributed. This breathing state appears in the low-detuning region between the MI-comb and stable-DKS regimes. In the doubly normal $(+/+)$ configuration, the relevant eigenvalue branches remain nearly degenerate in the MI band, and the Floquet sideband channel is strongly suppressed. In the nonlinear regime, periodic GVD reduces the residual ripples on the platicon plateau, while the peak power is almost unchanged.

Spatiotemporal optical vortex (STOV) pulses are localized electromagnetic wavepackets possessing a phase singularity in the plane containing the propagation direction. Such pulses have a transverse orbital angular momentum oriented perpendicularly to that plane. Here, we develop a general theory of STOV generation by resonant gratings operating at high-symmetry points. By studying the properties of the scattering matrix relating the incident and scattered diffraction channels of the grating, we demonstrate that a perfectly symmetric STOV appears when two particular channels are decoupled from each other and from all other channels at a high-symmetry point. The developed theory both explains why symmetric STOVs appear in several grating geometries proposed earlier and allows one to design new geometries for STOV generation. In particular, we design a grating for semi-guided STOV generation in the Littrow mounting and a grating generating simultaneously a pair of free-space STOVs in $\pm 1\mathrm{st}$ diffraction orders. The presented rigorous simulation results based on the Fourier modal method are in perfect agreement with the developed theory.