We develop a nonlocal minimal-coupling theory of structured-light dichroism. Optical absorption is written as a bilinear functional of the incident vector potential and the nonlocal current-response kernel, retaining the spatial structure of optical vortex beams and other inhomogeneous fields. Circular dichroism, helical dichroism, and helical circular dichroism are treated as distinct reversal channels that project different reversal-odd components of the same microscopic response. The resulting signal is resolved into symmetry, tensor, and angular-mode sectors. Single azimuthal-mode fields probe diagonal orbital-angular-momentum (OAM)-channel components, whereas mixed modes access off-diagonal mode-space coherence through interference between different OAM channels. The relative polarization of the mixed field further selects scalar, axial-vector, or rank-2 tensor sectors of the response. This decomposition gives selection rules for high-symmetry systems and a diagnostic scheme for low-symmetry nanophotonic structures, finite systems, and extended materials, where several angular-channel responses may coexist. It also connects the nonlocal current-response formulation to local-gradient descriptions based on spatial dispersion, optical chirality, and tensorial anisotropy.

The $2{}^3{S}_1\to 2{}^3{P}_2$ interval in positronium (Ps) has been measured using a phase-variation separated oscillatory fields method. The experiment was performed in a low-magnetic-field region using a beam of $2{}^3{S}_1$ atoms generated in a Xe gas cell via a charge exchange reaction. The Ps beam passed through two spatially separated microwave field regions whose relative phase was varied. The resonance frequency was obtained from the frequency dependence of the phase of the resulting interference signal, which was scanned over a range of less than 10 MHz. We obtained a value of $8626.82\pm 0.{48}_{\mathrm{stat}}\pm 0.{05}_{\mathrm{sys}}\mathrm{MHz}$, in good agreement with the theoretical value of $8626.78\pm 0.08\mathrm{MHz}$ calculated using $O\left(m_e{\alpha }^6\right)$ QED theory.

The quantum dynamics of ultracold collisions between rubidium atoms and excited metastable strontium ions is treated in the laboratory frame, enlightening the importance of the coupling between the internal angular momenta of the particles and their mutual rotation. The study reveals a subtle competition between electronic excitation exchange and fine-structure quenching, with no charge exchange, which is found to be very sensitive to the details of ion-atom interactions. The rate constant for electronic excitation exchange is found in agreement with the experimental results of Ben-shlomi et al. [Phys. Rev. A 102, 031301(R) (2020)], while the rate for fine-structure quenching is predicted to strongly depend on the initial polarization of the reactants.

The integration of single atoms with photonic integrated circuits promises scalable quantum information platforms, yet a fundamental challenge of trapping atoms into the near-field interaction region of the waveguide mode remains. Here we propose an on-chip waveguide-based nanolens, designed to focus a free-space incident Gaussian beam, thereby creating a tight optical beam directly above the waveguide surface. In contrast to treating the diffraction effect of the on-chip nanostructure as detrimental, our approach can utilize the effect to realize precise near-field positioning and trapping of single atoms, which allows strong coupling between the trapped atom and the guided photons in the waveguide. Through numerical simulation, we demonstrate that for a free-space input of an 852-nm Gaussian beam with a waist of $1\mu \mathrm{m}$, a waveguide can generate a near-field focused beam with a waist of only $0.66\mu \mathrm{m}$ and a height of about $0.07\mu \mathrm{m}$ above the waveguide surface, featuring a 3.0-mK dipole trap with only 3.5-mW free-space trap laser power assisted by a blue-detuned waveguide mode. The increase of atomic spontaneous emission rate induced by near-field atom-waveguide mode coupling is analyzed by the Purcell factor, which is up to $3.1\times {10}^{-3}$. Furthermore, it is demonstrated that the cold atoms can be transported from the trap center of the nanolens to the optical trap arrays created by the evanescent field of the waveguide modes. Our proposal provides a scalable approach for realizing a near-field waveguide-integrated single-atom array, paving the way toward hybrid photonic-atomic circuits for quantum applications.

We investigate the problem of mechanical stability in two-dimensional Bose-Fermi mixtures at zero temperature, focusing on systems with a tunable Bose-Fermi (BF) interaction and a weak but finite boson-boson (BB) repulsion. The analysis is carried out within the framework of the lowest-order constrained variational (LOCV) approach, which allows for a nonperturbative treatment of strong interspecies correlations while retaining analytical transparency. The BF interaction is modeled by a properly regularized attractive contact potential, enabling the exploration of both the attractive and repulsive energy branches. We determine the minimal BB repulsion required to ensure mechanical stability of the mixture by evaluating the inverse compressibility matrix over the full range of BF coupling strengths, within the domain of validity of the LOCV approximation. The interaction contribution to the energy is benchmarked against available experimental data and quantum Monte Carlo results in the single-impurity limit, showing good agreement. Our analysis reveals how the critical BB coupling depends on interaction strength, density imbalance, and mass ratio. In particular, we find that mixtures with equal boson and fermion masses exhibit enhanced stability, requiring the smallest BB repulsion to prevent mechanical instability. In this case, a relatively small BB interaction is sufficient to stabilize attractive mixtures for all values of the BF interaction. These results provide a theoretical framework for assessing stability conditions in experimentally realizable two-dimensional Bose-Fermi mixtures with tunable interactions.

We study the loss of the contrast in an atom interferometer when increasing the duration of Raman mirror pulses, and find the contrast decay rate to increase with the interferometer duration. We attribute this effect to the transverse spatial fluctuations of the intensity across the Raman beams, and to the dephasing induced by the associated light-shift inhomogeneities. Simulations based on the propagation of noisy synthetic Raman beams show that the contrast decay rate increases with the distance between the wave packets at the mirror pulse, before reaching an asymptotic limit when intensity fluctuations between the two wave packets become completely decorrelated. Finally, simulations based on the propagation of Raman beams having their measured intensity fluctuations predict contrast loss rates consistent with our measurements, confirming the detrimental role for the interferometer contrast played by intensity fluctuations across the interferometer laser beams.

The critical exponents and universality classes of localization transitions in quasiperiodic systems are of fundamental importance for understanding critical phenomena in aperiodic systems. Here we show that the dynamical critical behavior can be tuned without adding new terms or changing the form of the Hamiltonian by solely varying the incommensurate frequency of the quasiperiodic on-site potential. We construct a family of incommensurate frequencies from the limiting ratios of generalized Fibonacci sequences controlled by the parameters $(m,n)$ and use them to define the quasiperiodic on-site potential. By combining generalized fidelity susceptibility, localization-length scaling, and finite-size gap analysis, we find that the correlation-length exponent is insensitive to the choice of the incommensurate frequency and remains consistent with the correlation-length critical exponent, $\nu \simeq 1$, in the localization transition of the standard Aubry-André-Harper model. In contrast, the dynamical exponent extracted from the low-energy gap scaling varies systematically with the incommensurate frequency. Our results show that changing the incommensurate frequency provides a simple way to tune dynamical critical scaling in deterministic aperiodic systems. Our results suggest instead that the arithmetic structure of an irrational number can serve as a control parameter for nonequilibrium quantum dynamics, enabling the tuning of dynamical critical behavior without changing the microscopic Hamiltonian or the physical spatial dimension.

High-resolution microscopy of two-dimensional dipolar quantum gases requires selecting individual atomic layers, a task complicated for strongly magnetic lanthanide atoms by the limited applicability of standard magnetic-gradient techniques. We present an all-optical method for the deterministic spatial selection of single- and bilayer samples of cold dipolar atoms using spatially selective parametric heating within a beat-note superlattice. By utilizing a high-resolution microscope objective as a common retroreflector for both optical frequency components, the lattice planes are passively stabilized. This renders their positions exceptionally robust against experimental drifts and structure-borne vibrations, even eliminating the need for active laser stabilization over millimeter-scale separations from the reflecting surface. We validate this approach by demonstrating the robust isolation of one or two atomic layers in precise coincidence with the focal plane of our objective. This enables future single-atom-resolved studies of long-range interacting systems.

We report the experimental single-shot visualization and precise modeling of femtosecond laser filamentation in molecular gases and air. Experimentally, we control and enhance laser filamentation using rotational Raman effects by varying the pump-pulse duration and employ single-shot multiobject plane imaging to directly visualize long-range plasma channels and measure the associated plasma density. We compare experiments with nonlinear envelope equation simulations incorporating an alignment-dependent molecular Perelomov-Popov-Terent'ev ionization model, wherein Raman-induced molecular alignment dynamically modulates the ionization rate during filamentation. This approach provides a more accurate ionization model than commonly used atomic ionization approximations. Our work not only demonstrates robust single-shot visualization of filamentation but also highlights that alignment-dependent ionization is important for a comprehensive understanding of long-range filamentation in molecular gases and air.

Partially coherent vector beams generally undergo depolarization during propagation due to the incoherent superposition of spatial modes with different polarization states. Here we show that deterministic polarization states can, nevertheless, emerge in a partially coherent beam at a prescribed propagation distance. This effect is achieved by encoding mutually uncorrelated off-axis vector modes into a partially coherent and partially polarized source using a fractional Fourier transform optical system. During subsequent free-space propagation, the displaced vector modes evolve into overlapping and synchronized vector beams in a designed plane. As a result, the beam becomes fully polarized while remaining spatially partially coherent. The underlying mechanism is interpreted in terms of the cross-spectral density phase evolution of two orthogonally polarized partially coherent scalar modes that synthesize the partially coherent vector beam. Our results reveal a different route for controlling polarization structures in partially coherent light, with potential applications in optical angular momentum manipulation and optical trapping.

We investigate finite-width optical-beam propagation in a medium with uniform torsion described by the geometric theory of a continuous distribution of screw dislocations. Starting from the Riemann-Cartan framework that yields torsion-induced circular birefringence for local plane waves, we construct a minimal paraxial beam model in which the same contortion-driven helicity splitting remains explicit. The resulting beam equation is used as a controlled effective paraxial reduction, not as an exact finite-beam solution of the complete Riemann-Cartan Maxwell problem. Its validity assumes a predominantly forward beam $k_0{w}_0\gg 1$, weak effective optical detuning $|{\mathrm{\Omega }}_{\mathrm{o}}|w_0\ll k_0$ (equivalently $|{\mathrm{\Omega }}_{\mathrm{g}}|w_0\ll 1$), and slowly varying helicity phases over the transverse scale. We show that uniform torsion breaks the degeneracy between the two circular-polarization sectors and induces a geometry-induced helicity-dependent propagation phase that scales with both the propagation distance and the radial position in the beam. As a consequence, a finite-width beam develops spatially varying polarization textures across its transverse profile, naturally described by the Stokes parameters. We introduce beam-level observables based on the integrated Stokes vector, the transverse inhomogeneity of the polarization texture, and the number of resolved radial polarization domains, thereby connecting the torsion parameter to experimentally accessible beam diagnostics. The paper combines two complementary levels of description: an analytic short-distance regime, used to isolate the geometric mechanism, and full paraxial propagation including diffraction, used to test the robustness of the predicted textures. Within the cylindrically symmetric minimal model, the most robust structured-light signature of uniform torsion is beam-resolved polarization structuring, whereas strong orbital-angular-momentum conversion is not expected without additional azimuthal structure. We also discuss a deliberately extended, $q$-plate-like effective model only to identify the additional azimuthal geometric connection required for spin-orbit conversion; this extension is not presented as an intrinsic prediction of a uniform-torsion medium.

In wave-guiding structures, a bound state in the continuum (BIC) is a special guided mode with no leakage loss even though lateral radiation channels exist. The BICs are related to high-$Q$ resonances and have found numerous applications in photonics. A particularly simple class of BICs has been found in slab waveguides with an anisotropic core and anisotropic substrate [Gomis-Bresco et al., Nat. Photon. 11, 232 (2017)]. Many of these BICs are robust with respect to structural parameters. In this paper we demonstrate the robustness of BICs for a broad class of anisotropic waveguides of which the core is nonuniform in general. Using a perturbation method, we show that generic BICs persist when the structure is perturbed with any sufficiently small perturbation satisfying some simple conditions. The theory improves the theoretical understanding of BICs in anisotropic media and provides useful guidance for realizing their practical applications.

The stationary spectrum of individual dipole emitters in plasmonic nanocavities has been studied for a range of cavity geometries and dipole configurations. Less is known about the coherent dynamics of single-photon creation in the nanocavity near field by an excited dipole. We address this gap by developing a Lorentzian kernel approximation that solves the time-dependent Schrödinger equation that describes the coupled dipole-photon dynamics in the single-excitation manifold. Our approach encodes the broadband nature of the nanocavity field through a non-Markovian memory kernel, derived from macroscopic QED theory. For a two-level dipole near a metallic nanosphere, we show that the single-photon probability density in frequency space evolves in strong coupling from an initially localized source at the qubit frequency into a Rabi doublet over a timescale governed by the kernel spectrum. This dynamical crossover is accompanied by the formation of single-photon interference patterns in frequency and time, propagating coherently over a timescale limited by the shape of kernel spectrum to $\sim 100–150$ fs, which is accessible to ultrafast spectroscopy. We also show that the stationary spectrum of the coupled system can be manipulated by driving the nanocavity field using coherent pulses with variable spectral bandwidth. Using single-photon pulses narrower than the kernel spectrum, the Rabi splitting in a system that supports strong coupling can be effectively removed. The applicability of our results to other dipole-nanocavity configurations is discussed and a general strong coupling criterion for nanocavities is formulated.

Microlasers have emerged as a versatile platform for exploring quantum phenomena in light-matter interactions. Both photon counting and state detection of outgoing atoms are allowed for a microlaser with finite atomic transit time. However, the influence of probing atoms on microlaser dynamics and the consistency of light properties inferred from these two distinct detection schemes remain poorly understood. Here, we investigate the microlaser behavior under atomic state detection. We find that the projective state determination of outgoing atoms suppresses the photon emission and, unexpectedly, narrows the spectral linewidth in the low-transit-time regime. Furthermore, the atomic state detection fails to faithfully capture intrinsic cavity field properties, yielding biased estimates of microlaser properties. This work highlights the non-negligible perturbative role of probing atoms in microlaser dynamics, with fundamental implications for quantum measurement protocols and cavity quantum electrodynamics experiments.

We investigate the effective dynamics of a particle confined near a space curve. In the strict thin-layer reduction of the nondegenerate transverse ground state, torsion does not enter the local effective Hamiltonian, which contains only the curvature-induced scalar geometric potential. In contrast, for a thin guide with finite transverse width, a leading-order adiabatic projection onto the twofold-degenerate first excited transverse band renders the rotation of the Frenet normal frame dynamically relevant and generates a matrix-valued Abelian gauge potential. Using a projection-based derivation in a corotating Frenet-frame basis, we show that this effective gauge potential is directly determined by the local torsion of the curve. The resulting effective Hamiltonian takes a gauge-covariant form and produces two transverse-mode branches whose parabolic dispersions are shifted in opposite directions in momentum space. For closed curves, the associated holonomy is controlled by the integrated torsion and leads to geometric interference. These results provide a direct realization of a Wilczek-Zee-type connection induced purely by spatial geometry in curved quantum waveguides. We further construct a classical-wave analog using the degenerate bending modes of an isotropic elastic rod, demonstrating that the same torsion-induced gauge structure appears in continuum wave physics.

We analyze a Rydberg gate design based on the original $\pi -2\pi -\pi$ protocol [Jaksch et al., Phys. Rev. Lett. 85, 2208 (2000)] that is modified to enable high-fidelity operation without requiring a strong Rydberg interaction. The gate retains the $\pi -2\pi -\pi$ structure with an additional detuning added to the $2\pi$ pulse on the target qubit. The protocol reaches within a factor of 2.39 (1.68) of the fundamental fidelity limit set by Rydberg lifetime for equal (asymmetric) Rabi frequencies on the control and target qubits. We generalize the gate protocol to arbitrary controlled phases. We design optimal target-qubit phase waveforms to generalize the gate across a range of interaction strengths and we find that, within this family of gates, the constant-phase protocol is time optimal for a fixed laser Rabi frequency and tunable interaction strength. Quantum control techniques are used to design gates that are robust against variations in Rydberg Rabi frequency or interaction strength.

In far-field thermal radiation, electromagnetic waves emitted by an object propagate to infinity, requiring the far region to be modeled as an effective thermal bath. This bath was proposed as infinitesimal environmental “dust,” but explicit calculations with such distributed dust involve integrals over infinite space that are difficult to evaluate. In this work, we map this environmental dust to a photonic bath at infinity within the nonequilibrium photonic Green's-function formalism. By explicitly evaluating the spatial integral over the dust, we show that its contribution reduces to a simple local self-energy, for which we derive analytical expressions for both three-dimensional objects and planar systems. We further demonstrate that the bath behaves as a blackbody and clarify its role in far-field thermal radiation. An alternative derivation based on the surface Green's-function framework is also provided, demonstrating the theoretical consistency of the results without invoking the dust model. The photonic bath at infinity provides a convenient framework for both analytical and numerical calculations in far-field thermal radiation.

We analyze Fock-state lattices (FSLs) from an algebraic viewpoint. Starting from a Lie algebra, we associate a FSL constructed from the action of its generators: diagonal (Cartan) generators define the lattice sites, while off-diagonal (root) generators determine the lattice bonds. This construction reveals that identifying an underlying algebraic structure provides direct physical insight into FSLs, including their dimensionality, connectivity, symmetry constraints, and possible transport and revival phenomena. By examining several common Lie algebras, we identify not only their associated FSLs but also the corresponding Lie phase spaces, thereby establishing a systematic connection between FSL dynamics and phase-space geometry. In many cases, both the phase space and the FSL exhibit nontrivial curvature, opening possibilities for exploring quantum dynamics in curved synthetic spaces. We further address whether every integrable Hamiltonian admits an underlying Lie algebra that reproduces the same FSL structure. We show that this is not generally the case, particularly for Hamiltonians that are nonlinear in the generators, and that for systems combining different types of degrees of freedom the appropriate underlying structure may instead be a Lie superalgebra.