Intercavity polaritons, hybrid quasiparticles with spatially separated photonic and excitonic components, provide a platform to engineer structured light-matter states. We show that resonant driving of the middle polariton branch leads to a qualitatively distinct dynamical regime in which coherent Rabi oscillations are suppressed, and the system evolves monotonically toward its steady state. Including interactions, we demonstrate that this regime supports Bogoliubov excitations with a phononlike dispersion at low momenta. These collective modes inherit interactions from the excitonic fraction, while preserving the intrinsically intercavity nature of the quasiparticles.

We perform a joint experimental and theoretical study on Rydberg-state excitation (RSE) of argon in elliptically polarized strong laser fields with different wavelengths in the range of 800–1500 nm. It is observed that the RSE yield is suppressed with increasing ellipticity and such an ellipticity dependence is more significant for longer wavelengths. A three-dimensional classical trajectory Monte Carlo simulation well reproduces the experimental observations. It is indicated that Rydberg atoms originate from the electrons released within a certain survival window of the initial ionization phase and transverse velocity, which shifts more significantly as the wavelength increases. In addition, analysis of the final kinetic-energy distributions of the ionized electrons indicates that the low-energy electrons that can be recaptured into Rydberg states are depleted more rapidly with ellipticity for longer wavelengths. Our study sheds some light on the strong-field RSE in elliptically polarized lasers, showing that the recapture probability can be controlled by tuning the laser ellipticity and wavelength, reflecting changes in both the initial conditions at the tunneling exit and the electrons' final kinetic energy after tunneling.

Light-matter interactions within the strong-field regime, where intense laser fields can ionize a target via tunneling, give rise to fascinating phenomena such as the generation of high-order harmonic radiation (HHG) and, correspondingly, light pulses of attosecond duration. On the atomic scale, these strong-field processes are naturally described in terms of highly oscillatory time integrals which are often approximated using saddle-point methods. Those methods simultaneously simplify the calculations and let us understand the physical processes in terms of semiclassical electron trajectories, known as quantum orbits. However, applying saddle-point methods for HHG driven by polychromatic laser fields without clear dynamical symmetries has remained challenging. Here we introduce Picard–Lefschetz theory as a universal and robust link between the time integrals and the semiclassical trajectories, for arbitrary driving laser fields. The continuous deformation of the integration contour towards so-called Lefschetz thimbles allows for an exact evaluation of the integral, as well as the identification of relevant quantum orbits, independently of dynamical laser field symmetries or quantum-orbit classification heuristics. The latter is realized via the “necklace algorithm,” a solution to the open problem of determining the relevance of saddle points for a two-dimensional integral, which we introduce here. We demonstrate the versatility and rigor of Picard–Lefschetz methods by studying Stokes transitions and spectral caustics arising in HHG driven by two-color laser fields. For example, we showcase a quantum-orbit analysis of the color switchover, which links the regime of perturbative two-color fields with that of fully bichromatic driving fields. With this work, we set the foundation for a rigorous application of quantum-orbit-based approaches in attosecond science that enables the interpretation of state-of-the-art experimental setups, and guides the design of future ones.

Spin-resolved strong-field dynamics have recently emerged as a frontier in ultrafast and nonlinear optics, with growing evidence that spin effects can critically influence strong-field phenomena. Motivated by experimental observations of potassium atoms in atomic ionization in strong laser fields, where a characteristic photoelectron peak appears to exhibit an angular distribution related to the $m_l=1$ component, we solve the time-dependent Schrödinger equation including explicit spin-orbit coupling (SOC). Our calculations qualitatively reproduce the reported photoelectron momentum distribution and the characteristic peak, providing direct theoretical support for SOC-induced features in strong-field resonant multiphoton ionization. We show that the Autler-Townes splitting manifests as Rabi oscillations between the $S$ ground state and the resonant $P$ intermediate state, while the SOC further splits the dynamics into two phase-opposed Rabi oscillations between the $S$ and $P_{1/2}/P_{3/2}$ states, whose gradual dephasing during the electronic evolution gives rise to the characteristic peaks and directly links the yields to the SOC-induced level splitting. By unifying experimental observations, ab initio simulations, and a transparent Rabi-based framework, this work provides a coherent and physically intuitive understanding of spin-resolved strong-field ionization dynamics.

Nitrogen-vacancy (NV) centers in diamond are optically addressable and versatile light-matter interfaces with practical application in magnetic-field sensing, offering the ability to operate at room temperature and reach sensitivities below pT/$\sqrt{\mathrm{Hz}}$. We propose an approach to simultaneously probe all of the magnetically sensitive states using a broadband microwave field and demonstrate that it can be used to measure the external dc magnetic-field strength with sensitivities on the order of 10 pT/$\sqrt{\mathrm{Hz}}$. We develop tools for analyzing the temporal signatures in the transmitted broadband microwaves to estimate the magnetic field, comparing maximum-likelihood estimation based on minimizing the Kullback-Leibler divergence to various neural network models, and both methods independently reach practical sensitivities. These results are achieved without optimizing parameters such as the bandwidth and the shape of the probing microwave field such that further improvements in sensitivity can be envisioned. Our results motivate implementations of NV-based magnetic sensors with the potential for vectorial magnetic-field detection at (1–10)-kHz update rates and improved sensitivities without requiring a bias magnetic field.

We study the Born–Oppenheimer approximation of a mass-imbalanced three-body system made of two heavy particles of mass $M$ and one light particle of mass $m$ for arbitrary angular momentum. In this system, heavy-light pairs interact via a zero-range force. We construct the light-particle Hamiltonian using self-adjoint extensions of the two-center point interaction and show that the corresponding effective potential is regular at the coincidence point of the heavy particles. Consequently, this model presents an alternative method to finite-range, cutoff, or short-distance heavy-heavy regularizations: the necessary three-body input is encoded in the self-adjoint realization of the light-particle Hamiltonian, while the heavy-light interactions remain point-like. In the unitary limit, after fixing the characteristic length scale, we derive an explicit Efimov spectrum. Our results recover the zero-angular-momentum case of [J. Phys. A: Math. Theor. 57, 055303 (2024)] and provide a sufficient condition ensuring the absence of non-Efimov bound states. Away from unitarity, we show that the spatial size of the shallowest trimer near the threshold is approximately 2.8 times the heavy-light scattering length, in contrast with the common assumption that these two length scales coincide. We also derive a Bargmann-type bound on the number of three-body bound states and obtain an estimate sharper than previous results. Finally, we illustrate the method with numerical results for selected alkali mixtures.

We theoretically investigate the nonequilibrium relaxation of a spatial density modulation in a one-dimensional nonintegrable Bose gas and its connection to the equilibrium scattering rate ${\gamma }_k\propto k^{3/2}$ of the system's phononic excitations. We show that the density relaxation is generically governed by a nonequilibrium scattering rate ${\gamma }_{k,t}$ coupled to the time dependence of phonon occupations, which approaches its equilibrium value ${\gamma }_k$ only at long times. Numerical simulations of quantum kinetic equations reveal an algebraic convergence ${\gamma }_{k,t}-{\gamma }_k\sim t^{-2/3}$, confirmed by analytical predictions. More broadly, our results establish a theoretical framework for experimentally probing phonon dynamics through the temporal evolution of local perturbations in quantum gases.

Bose-Einstein condensates initially arranged in a long chain freely expand and interfere. If the initial phases of the condensates are identical, the initial density distribution is restored periodically during the expansion, giving rise to the Talbot effect. Even a slight disorder in the initial phases leads to a transformation of the interference pattern. In response to the phase disorder, the spectrum of the spatial density distribution acquires peaks that are absent in the case of identical phases. We derive an analytical expression for the spectrum of the spatial density distribution for an arbitrary phase disorder. We show that the new peaks emerging due to the phase disorder originate from pairwise interferences of the condensates. The positions of these peaks coincide with the wave vectors of the density modulations (wavelets) generated by such pairwise interferences. The absence of these peaks, when the initial phases are identical, is explained by the mutual destruction of the overlapping wavelets during their summation.

The relaxation of a quantum field from a metastable state (false vacuum) to a stable one (true vacuum), also known as false-vacuum decay, is a fundamental problem in quantum field theory and cosmology. We study this phenomenon using a two-dimensional interacting and coherently coupled Bose-Bose mixture, a platform that has already been employed experimentally to investigate false-vacuum decay in one dimension. In such a mixture, it is possible to define an effective magnetization that acts as a quantum field variable. Using the stochastic projected Gross-Pitaevskii equation (SPGPE), we prepare thermal equilibrium states in the false vacuum and extract decay rates from the magnetization dynamics. The decay rates show an exponential dependence on temperature, in line with the thermal theory of instantons. Since the SPGPE is based on complex scalar fields, it also allows us to explore the behavior of the phase, which turns out to become dynamic during decay. Our results confirm the SPGPE as an effective tool for studying coupled magnetization and phase dynamics and the associated instanton physics in ultracold quantum gases.

We analyze the spectral three-dimensional (3D) polarimetric properties of the electric and magnetic fields in an evanescent wave created by a random stationary light beam undergoing total internal reflection. In particular, we compare the degrees of polarimetric purity, polarimetric dimensions, nonregularity properties, and spin-density vectors of the electric and magnetic fields and further assess the total spin angular momentum density. We show, e.g., that some properties are determined exclusively by the geometry and that in certain situations the polarization states of both fields can display a true 3D nonregular character. In addition, the electric and magnetic spin-density vectors generally consist of transverse and longitudinal components and possess a specific polarimetric structure for nonregular states.

Photon statistics plays a governing role in multiphoton interference. While interference visibility in the standard two-photon case, known as Hong-Ou-Mandel interference, monotonically degrades with higher intensity correlation functions, we show that this monotonicity does not hold for three-photon interference in symmetric circuits. We reveal that, in the discrete Fourier transform circuit, engineered super-Poissonian photon-number fluctuations, realized using a modulated laser, can yield a visibility whose magnitude surpasses that of the single-photon signature. In addition, by tuning the symmetric circuit parameters, we demonstrate that the visibility hierarchy inverts relative to the benchmark of Poissonian statistics. This trade-off implies that quantum and classical advantages are mutually exclusive resources for interference, indicating a form of statistical complementarity.

We propose an extended Su-Schrieffer-Heeger chain that integrates long-range hopping and a synthetic Peierls phase, providing a tunable circuit platform to trigger and control non-Hermitian transitions and topological phase transitions. We show that the long-range hopping strength acts as a trigger for topological phase transitions, destabilizing edge states through band-gap closure. Simultaneously, the Peierls phase serves as a synthetic gauge field, enabling active and reversible switching between trivial and topological regimes via phase-selective coupling. Under balanced gain and loss, topological edge states remain robust but undergo dramatic reconstruction at exceptional points, accompanied by non-Hermitian skin effects and complex spectral loops. Furthermore, we discover rich wave-packet dynamics under parameter tuning, including phase-dependent localization, spectral winding, and anomalous diffusion near exceptional points. Our work establishes a highly tunable circuit framework for dynamically coupling topological, non-Hermitian, and transport phenomena, offering direct pathways toward robust topological photonics, enhanced sensing, and synthetic quantum matter.

Quantum processes can exhibit scenarios beyond a fixed order of events. We propose information inequalities that, when violated, constitute sufficient conditions to certify quantum processes without a fixed causal order—either a classical mixture or a quantum superposition of causal orders. The inequalities hold valid for a vast class of information measures. Nevertheless, we take under scrutiny the von Neumann, $\alpha$-Rényi entropies with parameter $\alpha \in [1/2,1)\cup (1,\infty )$, and max- and min-entropies. We also discuss how the strong subadditivity of quantum (von Neumann) entropy, used along with the information inequality developed here, implies relevant witnesses of nonfixed causal order in marginal scenarios. Importantly, we show the violation of these inequalities for the quantum switch, a paradigmatic example of a process with indefinite causal order.

We develop a general theory of Landau-Zener (LZ) tunneling in a two-level system with amplitude-dependent, sign-reversible nonlinear coupling, distinguishing it fundamentally from conventional on-site nonlinearity. Through a combination of analytical and phase-space analysis, we show that beyond a critical interaction strength, the nonlinear coupling fundamentally reshapes the adiabatic energy landscape, introducing a topological twisted and knotted structure. This structure leads to a complete breakdown of the standard exponential LZ formula, even in the adiabatic limit. Central to this anomalous behavior is the emergence of a universal-attractor fixed point, which acts as a universal attractor: Upon traversing the critical region, all quantum trajectories converge to this fixed point, irreversibly erasing any memory of the initial state. From this fixed-point picture, we derive an exact analytical expression for the adiabatic tunneling probability, revealing a characteristic power-law dependence on both linear and nonlinear coupling strengths. Our work establishes a paradigmatic framework for nonlinear-coupling-induced anomalous adiabaticity breaking and offers a universal mechanism for state control in driven quantum and wave systems.

We investigate the statistical properties of orthogonal, or real, Clifford circuits doped with magic and imaginary resources. By developing the Weingarten calculus for the real Clifford group, we derive the exact overlap distribution of real stabilizer states, identifying a different universality class: the orthogonal Clifford Porter-Thomas distribution. We prove that local real architectures recover this global statistic in logarithmic depth. Furthermore, we uncover a sharp hierarchy in resource requirements: while retrieving Haar statistics necessitates a polylogarithmic amount of magic states, recovering the full unitary Clifford statistics requires only a single phase gate.

We present a general theoretical treatment and calculations of the fine and hyperfine structures in the spectra of high-$n$ molecular Rydberg states in static uniform electric fields. The treatment combines (i) multichannel quantum-defect theory and long-range polarization models to determine the field-free energies of $n\ell$ Rydberg states of the molecules ($\ell$ is the orbital-angular-momentum quantum number of the Rydberg electron), (ii) a matrix-diagonalization approach to calculate the Stark shifts including the hyperfine structure, and (iii) sequences of angular-momentum basis transformations to predict the line positions and intensities in Stark spectra as they would be observed in single or multiphoton excitation sequences. To clarify how the molecular rotation and the nuclear spins influence the fine and hyperfine structure of molecular Rydberg-Stark spectra, we compare calculated spectra of ortho-${\mathrm{D}}_2$ with a ${\mathrm{D}}_2^{+}$ ion core in the rotational ground state ($N^{+}=0$) for total nuclear spins $I$ of 0 (i.e., without hyperfine structure) and 2 (i.e., with hyperfine structure) with the corresponding spectra of para-${\mathrm{H}}_2$ with an ${\mathrm{H}}_2^{+}$ ion core in the first excited rotational state ($N^{+}=2$) but zero nuclear spin ($I=0$). The calculations show that the hyperfine interaction alone does not significantly modify the Stark effect, but splits each Stark state by almost exactly the hyperfine Fermi-contact splitting of the ion core. In contrast, the molecular rotation, which is coupled both to the ion-core electron spin by the magnetic spin-rotation interaction and to the Rydberg-electron orbital motion by the core-polarization and charge-quadrupole interactions, induces Stark-state-specific splittings that significantly differ from the spin-rotation splitting of the ($N^{+}=2$) ion core.

Laser-cooled trapped ions are at the heart of modern quantum technologies and their cooling dynamics often deviate from the simplified two-level atom model. Doppler cooling of the ${}^{88}\mathrm{Sr}^{+}$ ion involves several electronic levels and repumping channels that strongly influence fluorescence. In this work, we study a repumping scheme for the ${}^{88}\mathrm{Sr}^{+}$ ion by combining precision single-ion spectroscopy with comprehensive numerical modeling based on optical Bloch equations including 18 Zeeman sublevels. We show that, although the observed fluorescence spectra retain a Lorentzian line shape, their width and amplitude cannot be explained by a two-level atom description. Moreover, we find the optimal repumping conditions for maximizing the photon scattering rate.

The continuous spontaneous localization (CSL) model is one of the most promising approaches to address the wave-function collapse problem in the measurement process of standard quantum mechanics. In this work, the effect of the CSL model on a Bragg atom interferometer is investigated. A Bragg interferometer achieving high fringe contrast of $99\%$ is demonstrated, maintaining this performance level at an interrogation time of up to $T=60\mathrm{ms}$. The primary factors responsible for fringe contrast loss in the atom interferometer are systematically analyzed and corrected. This improvement establishes an upper limit of ${\lambda }_{\mathrm{CSL}}=1.27\times {10}^{-5}{\mathrm{s}}^{-1}\mathrm{at}{r}_C={10}^{-5}\mathrm{m}$ for the CSL collapse rate, representing approximately 4 times enhancement over previous atom-interferometric constraints.

An atomic Josephson junction realized with dipolar bosons in a double-well potential can be described by an extended Bose-Hubbard model in which dipolar interactions generate an effective on-site interaction and nearest-neighbor pair tunneling. Using mean-field theory and exact diagonalization, we investigate how this correlated process affects zero-temperature equilibrium and dynamical properties of the system. In equilibrium, we show that pair tunneling induces ground-state parity modulations and significantly reshapes the phase diagram, producing qualitative changes in the quantum phase transitions toward NOON and phase-NOON states, as well as quantitative shifts of the critical points. Out of equilibrium we demonstrate that it modifies the conditions for macroscopic quantum self-trapping, and assess its impact by comparing mean-field and fully quantum evolution, including the emergence of dynamical quantum phase transitions.