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.

We propose a coherent-control scheme for engineering quantum correlations in a cavity optomechanical (COM) system consisting of a driven optical cavity with an embedded nonlinear medium and a membrane, assisted by a coherent feedback loop. The nonlinear medium and the membrane are pumped to implement optical and mechanical parametric amplifications with controllable modulation frequencies and pump amplitudes. Within the stable regime identified by Floquet analysis, the feedback-induced enhancement of optomechanical entanglement persists when the period-averaged mean-field intracavity photon number is matched, showing that the enhancement cannot be attributed simply to an increase in this quantity. A systematic comparison of the four configurations further reveals a nonadditive interplay between dual parametric amplification and coherent feedback. Varying the amplitude reflectivity of the beam splitter and the feedback-loop phase enables effective control of optomechanical entanglement and directional Einstein-Podolsky-Rosen steering, including a transition from one-way to two-way steering. The combined scheme also improves the robustness of both correlations against thermal noise, providing a potential route toward robust quantum-state engineering in COM systems.

We show that a driven-dissipative cavity-magnonic dimer supports multistability with coexisting symmetric and symmetry-broken steady states. The interplay between magnon Kerr nonlinearity and photon tunneling induces magnon self-trapping, leading to a persistent population imbalance between the two resonators. In the vicinity of saddle-node bifurcations, the system exhibits critical slowing down, with relaxation times far exceeding the intrinsic dissipation scale and critical exponents close to the universal saddle-node value $\alpha =1/2$. Beyond the semiclassical dynamics, we probe fluctuation signatures through the quantum fidelity and mutual information between the two magnon modes. We find that both the infidelity and the mutual information increase sharply near the phase boundaries, providing signatures of the multistable and symmetry-broken phases. Our results establish cavity magnonic dimers as a versatile platform for exploring nonlinear nonequilibrium physics in hybrid quantum systems.

We present the results of an experimental study of the anomalous anisotropy of alignment signals in cesium vapors under strong spin-exchange conditions near zero magnetic field with linearly polarized optical pumping. We show that the anisotropy of the Hanle resonances in the plane perpendicular to the pump beam increases with Cs vapor number density: In one direction the widths remain broadened by spin exchange, whereas in the other they approach the spin-exchange relaxation-free limit. With a further increase in number density, additional nonlinear effects arise such as signal amplification, bistability, hysteresis, and memory. To explain these effects we construct an illustrative theoretical model incorporating spontaneous polarization effects under strong-spin-exchange conditions. The model qualitatively shows that the ultranarrow alignment resonances may originate from quadrupole anisotropy arising from the projection of spontaneous transverse orientation onto the detection axis. The unique properties of these resonances, such as their extremely small width and magnetic-field-controlled bistability with a long-term memory effect, make them promising for use in quantum sensing and information.

Waveguide quantum electrodynamics provides a powerful platform for exploring quantum optical phenomena by enhancing atom-photon interactions through photon confinement in a waveguide. Here we investigate the photon-scattering dynamics of a weak coherent pulse incident from the left on a giant atom coupled to a bidirectional waveguide, focusing on effects absent in the small-atom approximation. Using an extended input-output formalism, we calculate the relevant correlation functions and show that the competition between two scattering processes is governed by the ratio of the pulse width to the atomic lifetime, leading to time-dependent switching between bunching and antibunching. In addition, tuning the phase accumulated between the two coupling points of the giant atom allows the photon statistics to be switched among three distinct regimes, each with a finite phase bandwidth. We also discuss the experimental feasibility in superconducting circuits. Our results provide a route toward giant-atom-based control of photon pulses and potential applications in quantum control.

We formulate Zeno and anti-Zeno dynamics in a finite-memory reservoir as a time-domain measurement-filter problem. A two-level system exchanges an excitation with a finite chain of damped memory modes and is subjected to repeated partial, nonselective measurements. In the weak-coupling limit, the population decay rate is written as an overlap between a finite reservoir memory kernel and a measurement-dependent filter. For any finite chain, this separation gives a compact expression that connects pulsed and continuous monitoring while retaining correlations across successive measurement intervals. When all memory-mode frequencies are tuned to the two-level transition, a single lossy mode gives monotonic Zeno suppression, whereas two modes form the smallest chain that can produce anti-Zeno-to-Zeno switching without an externally imposed onsite detuning. Exact stroboscopic Liouvillian calculations verify the analytic filter prediction and quantify finite-coupling corrections. For longer chains, the response is controlled by the frequencies, lifetimes, and boundary weights of the memory poles rather than by chain length alone.

Non-Gaussian operations are essential for most bosonic quantum technologies. Yet, realizable non-Gaussian gates are rather limited in type and generally suffer from accuracy-duration trade-offs. In this work, we propose to use quantum signal processing (QSP) techniques to engineer non-Gaussian gates on hybrid qumode-qubit systems. For systems with dispersive coupling, our scheme can generate a non-Gaussian gate that produces a phase shift depending on the modulus of the boson number. This gate reproduces the selective number-dependent arbitrary phase gates under certain parameter choices, but with higher accuracy within a short, fixed, and excitation-independent interaction time. The gate unlocks different applications, for example, in entangling logical qudits and deterministically generating multicomponent cat states. Additionally, our versatile QSP formalism can be extended to systems with other interactions and also engineer nonunitary operations, such as noiseless linear amplification and generalized-parity measurement.

The simulation of strongly correlated fermionic systems remains a significant challenge in computational physics due to the exponential growth of the Hilbert space and the fermionic sign problem. In this work, we report a quantum computing demonstration exploring the unified physics of the Fermi polaron and the Bose-Einstein condensate to Bardeen-Cooper-Schrieffer crossover. We develop an effective Hamiltonian formalism that bridges pairing superfluidity and impurity physics, mapping the system onto a gate-based quantum processor via the Jordan-Wigner transformation. By utilizing a first-order Trotter-Suzuki decomposition, we implement an ancilla-controlled Ramsey interferometry protocol to resolve the system's spectral response. Our implementation captures the smooth transition from a dressed quasiparticle (polaron) regime to a stable molecular bound state, characterized by a linear energy renormalization in the strong-coupling limit. We benchmark the quantum protocol against exact diagonalization and demonstrate its execution on the Barcelona Supercomputing Center quantum hardware. To ensure reproducibility, we provide comprehensive device calibration metrics, including qubit coherence times and gate fidelities at the time of execution. Despite inherent hardware noise, the hybrid variational approach qualitatively observes the bifurcation of the spectral density.

Due to the recent availability of intense, short, XUV laser pulses, the investigation of the Autler-Townes (AT) doublet in resonant ionization phenomena is experiencing a renaissance. In particular, the asymmetry of the AT doublet was found to be sensitive to numerous physical parameters, providing a promising tool to probe and control the bound-state electron dynamics. Recently, the exact analytic evaluation of the AT doublet under rectangular pulse driving [A. Csehi, Phys. Rev. A 113, 033121 (2026)] provided a unified picture, revealing that the asymmetry is attributed to three main factors: (i) the interference of different ionization pathways, (ii) the distinct decay rates of the emerging dressed states, and (iii) the energy dependence of the bound-to-continuum couplings. Here, going beyond the constant envelope approximation, we identify the finite nature of the rising and falling edges of the laser pulse envelope function as an additional source of the asymmetry. Smoothly varying the envelope from a rectangular to a realistic pulsed profile (e.g., Gaussian), we show that the relative phases of the delayed photoelectrons, which are released at the temporal slits opened up by the Rabi cycling atom, can be efficiently modulated. This allows for the interference control of the electron yields at the main AT peaks. The found general asymmetry effect primarily hinges upon the asymmetry of the dressed-state energies in the continuum, caused by detunings or ac Stark shifts, and thus efficiently modified by the parameters of the laser, like intensity, photon frequency, and duration.

We investigate the quantum optical properties of high-harmonic generation in semiconductors, focusing on the nonclassicality and entanglement of harmonic modes. By conditioning the emitted field on harmonic excitation, we obtain conditional harmonic states that exhibit pronounced nonclassical features in the plateau region. For harmonic photon energies above the minimum energy gap, the conditional states associated with interband transitions exhibit significantly stronger entanglement and nonclassicality than those associated with intraband processes. These results reveal how microscopic interband and intraband electron dynamics determine the quantum properties of conditional harmonic states, providing insight into the microscopic origin of nonclassical features in high-harmonic generation and highlighting the potential for generating nonclassical extreme-ultraviolet light sources.

We investigate the dynamics of Bose-Einstein-condensate droplets composed of ${}^{164}\mathrm{Dy}$ atoms formed in a double-well potential following removal of the interwell barrier. By solving the dipolar Gross-Pitaevskii equation, we determine phase diagrams of ground-state configurations as functions of the number of atoms confined in the double-well potential. For an interwell separation $2d=3\mu \mathrm{m}$, we consider the relative dipolar-to-contact interaction strengths ${\varepsilon }_{dd}=1.4$, 1.45, and 1.5. Symmetry-broken lowest-energy configurations are found for ${\varepsilon }_{dd}=1.5$ and, over a reduced range of numbers of atoms, for ${\varepsilon }_{dd}=1.45$, whereas no symmetry-broken states are found for ${\varepsilon }_{dd}=1.4$ up to $N=5\times {10}^4$. We analyze the subsequent time evolution after removal of the central barrier, revealing both droplet oscillations and merger events leading to the formation of larger droplets. The oscillations are driven by the external potential and by the repulsive tails of the in-plane component of the dipolar interaction. For the two-droplet states at ${\varepsilon }_{dd}=1.5$ and $2d=3\mu \mathrm{m}$, merging is found for $N=8000$ and 8800, whereas the droplets remain separated for the investigated cases with $N\ge 9000$. Increasing the initial separation to $2d=5\mu \mathrm{m}$ shifts the approximate upper number of atoms for merging to $N\simeq 1.65\times {10}^4$, demonstrating that the crossover is controlled by the competition between the postquench excess energy and the repulsive interdroplet barrier.

We propose to measure the dispersions of Fermi polaron and molecule by engineering spin-orbit coupling (SOC) on the impurity, which induces spin flip with finite momentum transfer. The polaron dispersion can be probed at small SOC momentum from the linear response of impurity spin. For molecule, we show that it can be prepared through an adiabatic steady-state evolution when setting SOC momentum as the Fermi momentum of majority bath. By gradually reducing SOC strength to zero, the steady state smoothly evolves to a molecular state with directional symmetry breaking. The corresponding dispersion can then be probed experimentally through the pair momentum distribution of molecules at finite density. Our scheme reveals a fundamental momentum difference between Fermi polaron and molecule, thereby offering a clear physical picture for their first-order transition in single-impurity system.