Above-threshold ionization (ATI) is a strong-field-driven process where electrons absorb more photons than required for ionization. While ATI dynamics and outputs are well-understood when driven by classical, perfectly coherent light, the recent development of nonclassical light sources for strong-field phenomena has spurred interest in their effect on the involved electron dynamics. In this work, we present a microscopic quantum optical theory describing ATI under the influence of strong squeezed light. We observe that squeezed light significantly enhances the coupling between light and matter, making their mutual backaction more important than under classical driving. This backaction profoundly impacts the electronic ionization times, as well as the nonclassical properties of the joint electron-light state. This results in pronounced entanglement features, both immediately after ionization and at later times. These entanglement features are reflected in the properties of the quantum optical state of the driving field, revealing notable non-Gaussian features that depend on both the amount of squeezing and the number of ionization events occurring during the interaction.

We present a combination of the R-matrix theory with time dependence (RMT) method with density matrix theory to model sequential ionization processes. Separate RMT calculations model the individual ionization stages, while a density matrix describes the coherences within the intermediate ion. As proof of concept, we quantify changes in the angular distribution of photoelectrons in the final stage of sequential ionization of $\mathrm{Ne}{}^{+}$ to ${\mathrm{Ne}}^{3+}$ by x-ray free-electron laser radiation with photon energies of 95 eV.

Precise individual addressing of single atoms in quantum registers formed by optical trap arrays is essential to achieve high-fidelity quantum gates in neutral-atom quantum computers and simulators. Two-qubit quantum gates are typically implemented using coherent two-photon laser excitation of atoms to strongly interacting Rydberg states. However, two-photon excitation encounters challenges in individual addressing with tightly focused laser beams due to atom position uncertainty and the spatial inhomogeneity in both Rabi frequencies and light shifts. In this work, we theoretically demonstrate that the fidelity of individual addressing is significantly enhanced by employing coherent three-photon laser excitation of Rydberg states. For a specific example of $5s_{1/2}\stackrel{{\mathrm{\Omega }}_1}{\to }5p_{3/2}\stackrel{{\mathrm{\Omega }}_2}{\to }7s_{1/2}\stackrel{{\mathrm{\Omega }}_3}{\to }np$ excitation in ${}^{87}\mathrm{Rb}$ atoms, we find that upon strong laser coupling in the second step (Rabi frequency ${\mathrm{\Omega }}_2$) and moderate coupling in the first and third steps (Rabi frequencies ${\mathrm{\Omega }}_1$ and ${\mathrm{\Omega }}_3$), the three-photon Rabi frequency is given by $\mathrm{\Omega }={\mathrm{\Omega }}_1{\mathrm{\Omega }}_3/{\mathrm{\Omega }}_2$. If the spatial distributions of $\left({\mathrm{\Omega }}_1{\mathrm{\Omega }}_3\right)$ and ${\mathrm{\Omega }}_2$ are arranged to be identical, $\mathrm{\Omega }$ becomes independent of atom position, even within very tightly focused laser beams. This approach dramatically improves individual addressing of Rydberg excitation for neighboring atoms in trap arrays compared to conventional two-photon excitation schemes. Our findings are crucial for large-scale quantum registers of neutral atoms, where distances between adjacent atoms should be minimized to ensure stronger Rydberg interactions and compact arrangement of atom arrays.

Ji et al. [New J. Phys. 26, 093014 (2024)] established a direct link between the photoionization cross section and the attosecond time delay near Cooper minima (CM) in the valence shells of noble-gas atoms. This link is based on the analytic properties of the ionization amplitude in the complex plane of the photoelectron energy, and is particularly sensitive to the winding number of the amplitude around the origin of the complex energy plane. Here, we demonstrate an analogous relation for photoionization of the valence $ns$ shells of alkali-metal atoms (AMA), from Na $(n=3)$ to Cs $(n=6)$, as well as alkaline-earth-metal atoms (AEMA), from Mg $(n=3)$ to Ba $(n=6)$. To this end, we employ a fully relativistic formalism that separates the two complementary $n{s}_{1/2}\to E{p}_{1/2}$ and $E{p}_{3/2}$ ionization channels. Each of these channels exhibits a phase variation close to $\pi$, but in opposite directions, near their respective Cooper minima. This phase variation vanishes in a nonrelativistic formulation, where the two channels become degenerate. For AMA, due to the threshold proximity of the CM, the universal Coulomb contribution to the time delay must be subtracted. The remaining component of the time delay is target-specific, angular-dependent, and accessible through comparative measurements.

Three-body loss resonances associated with heavy-heavy-light Efimov states have been observed for over a decade in ultracold mixtures tuned near interspecies Feshbach resonances. For light-light-heavy systems, observing such resonances has been far more challenging due to the substantially large Efimov spacing. In these Efimov-unfavored systems, the intraspecies scattering length $a_{\text{BB}}$ has been shown to significantly affect the overall Efimov scenario, namely, the positions of the Efimov resonances $a_{-}^{\left(n\right)}$ and the three-body parameter (3BP) $a_{-}^{\left(0\right)}$. The present article explains the origin behind this influence by highlighting two primary mechanisms via which both the magnitude and sign of $a_{\text{BB}}$ govern the Efimov spectrum and set the resulting 3BP $a_{-}^{\left(0\right)}$. By employing van der Waals interactions for ${{}^{23}\mathrm{Na}}_2{}^{40}\mathrm{K}$, we attribute the vital role of $a_{\text{BB}}$ in Efimov-unfavored systems to the large difference between the Efimov scaling parameters for two and three resonant interactions, $s_0$ and $s_0^{*}$. In particular, we account for the unusually large $a_{-}^{\left(0\right)}$ obtained in light-light-heavy systems with $a_{\text{BB}}>0$ (e.g., ${{}^{41}\mathrm{K}}_2{}^{87}\mathrm{Rb}$), and show that the first Efimov resonance can still occur at an experimentally accessible value when $a_{\text{BB}}<0$.

Making use of refermionization techniques, we map the nonlinear chiral Luttinger liquid model of the edge modes of a spatially confined fractional quantum Hall cloud developed in our recent work [Nardin et al., Phys. Rev. A 107, 033320 (2023)] onto a one-dimensional system of massive and interacting chiral fermions, whose mass and interactions are set by the filling factor of the quantum Hall fluid and the shape of the external confining potential at the position of the edge. As an example of the predictive power of the refermionized theory, we report a detailed study of the dynamic structure factor and of the spectral function of a fractional quantum Hall cloud. Among other features, our refermionized theory provides a physical understanding of the effective decay of the edge excitations and of the universal power-law exponents at the thresholds of the dynamic structure factor. The quantitative accuracy of the refermionized theory is validated against a full two-dimensional calculation based on a combination of exact diagonalization and Monte Carlo sampling.

We investigate parametric excitation and pattern formation in a harmonically trapped two-component Bose-Einstein condensate. We assume the condensate to be in the miscible phase, but near the miscible-immiscible phase transition, where total-density and spin-density excitations are decoupled. By periodically modulating the atomic scattering lengths, Faraday patterns can be generated in both density and spin channels. In an elongated condensate, the pattern in the spin channel corresponds to a one-dimensional standing wave with the two components exhibiting an out-of-phase density oscillation, where the modulation frequency and the oscillation period are related to the velocity of the spin sound. After the spin pattern is fully developed, the system quickly enters a nonlinear destabilization regime. For a pancake-shaped condensate, a two-dimensional Faraday pattern is generated with an interesting $l$-fold rotational symmetry. The number of nodes along the radial and angular directions increases with larger modulation frequencies. We also compare the growth rates of spin Faraday patterns generated with different modulation protocols, which are accessible to current experiments.

We show that the Keldysh parameter, which plays a central role in laser-driven ionization in atoms, molecules, and solid-state physics, can be meaningfully extended to strong-field laser-nucleus interaction settings, providing a key benchmark for laser-assisted nuclear dynamics, including the dynamics that drives nuclear fusion. We demonstrate that, similar to its counterpart in atomic, molecular, and solid-state physics, the nuclear Keldysh parameter, ${\gamma }_{\mathrm{n}}$, can be defined via the square root of the ratio of the height of the potential barrier separating the reactant and product states of a quantum system to the kinetic energy that a reduced-mass particle representing the respective two-body interaction acquires from the laser field. Adding to a striking parallelism with atomic, molecular, and solid-state physics, the ${\gamma }_{\mathrm{n}}\approx 1$ borderline is shown to separate two distinctly different regimes of quantum dynamics in laser-nucleus interactions. While in the ${\gamma }_{\mathrm{n}}\gg 1$ regime, such interactions are adequately described in terms of the standard Gamow tunneling exponential; in the ${\gamma }_{\mathrm{n}}\ll 1$ regime, the Gamow-exponential approximation fails, as the tunneling of nuclear wave packets becomes strongly dispersive, connecting to the zeptosecond dynamics of laser-field-dressed nuclear wave functions.

Lithium niobate on insulator (LNOI) offers the opportunity for chip-scale self-referenced frequency standards by enabling simultaneous ultrabroadband supercontinuum and second-harmonic generation. This is achieved through precise dispersion engineering and strong, diverse nonlinearities of submicron waveguides with low pump power. Out of consideration for low-power, chip-scale applications where the pump power is limited, optimizing the waveguide dispersion and extending the waveguide length are essential to achieve enhanced spectral flatness and improved energy efficiency. In this work, we report ultrabroadband supercontinuum generation on a dispersion-engineered waveguide on LNOI, achieving a 30 dB spectral bandwidth of over 1650 nm under a pulse energy below 80 pJ. Based on the above generated supercontinuum spectrum, we measured spectra1 response of two integrated edge coupler designs—monolayer and bilayer taper structure from 600 to 2400 nm. This chip-scale supercontinuum source offers low energy consumption, integration, and high coherence, making it a compelling complement to commercial sources and enabling applications, including spectroscopy, optical coherence tomography, midinfrared sensing, and quantum photonics.

Periodic driving can induce the emergence of topological $\pi$ modes, and their superposition with zero modes leads to two-period dynamics. Introducing long-range couplings enables the realization of larger topological winding numbers, which correspond to multiple pairs of degenerate edge states under open boundary conditions. In this work, we construct a Floquet extended Su-Schrieffer-Heeger (SSH) model by introducing a two-step periodic driving and next-nearest-neighbor coupling into the static SSH chain simultaneously. Remarkably, we identify anomalous edge states with quasienergies $\pm \pi /3T$ and $\pm 2\pi /3T$. In order to reveal the dynamical features of these anomalous edge states, we elaborately adjust the optical parameters and ultimately achieve a successful mapping of the model onto a photonic waveguide array. Subsequently, through numerical simulation of the wave equation, we observe the unique behavior of three-period evolution. Our work may serve as a reference for realizing period-multiplied dynamics, and the anomalous edge states discussed here might also find applications in quantum computation.

In this work, we study electromagnetic wave propagation in slab waveguides whose core is a topological insulator characterized by a topological magnetoelectric parameter. Topological insulators are materials that are electrically insulating in the bulk but support robust conducting states at their boundaries, protected by time-reversal symmetry. Their electromagnetic response is described by an axionlike term that modifies Maxwell's electrodynamics (ED), leading to rich and unconventional phenomena, as the topological magnetoelectric effect. We find that all modes supported by these structures are all exact hybrid modes with nonvanishing longitudinal field components. This hybridization is a direct consequence of the modified boundary conditions produced by the topological term and is absent in topologically trivial, reciprocal, and nonchiral slab waveguides. Modifications to the propagation condition and ensuing modes are shown for the case of an asymmetric slab; however, the detailed solution of the exact modes, coupling of modes and the dispersion relations is made for the symmetric slab. By solving the full $\mathrm{\Theta }$ electrodynamics equations nonperturbatively, we derive the modal dispersion relations and explore polarization rotation and power transfer between modes. Our approach reveals qualitative and quantitative deviations from standard coupled-mode theory and captures different signatures of the topological magnetoelectric response. To compare with other approaches to the subject and owing to the smallness of the $\mathrm{\Theta }$ effects, we perform a perturbative analysis of mode propagation, also based on writing a general solution as a superposition of exact modes of $\mathrm{\Theta }$-ED but expanding to first nonvanishing order in $\mathrm{\Theta }$. Also we apply the methodology of coupled-mode theory. This last approach is predicated on building solutions as superpositions of modes of ordinary electrodynamics that fail to satisfy the boundary conditions imposed by the $\mathrm{\Theta }$ term but compensate at the expense of modifying the field profiles. These findings provide a comprehensive framework for light control in topological photonics and potential routes to experimentally probe the magnetoelectric effect in guided settings.

Cutting-edge quantum technologies lean on sources of high-dimensional entangled states (HDESs) that reliably prepare high-fidelity target states. The idea to overlap photon paths from distinct but indistinguishable sources was recently introduced for the creation of HDESs, known as entanglement by path identity. In this regard, the use of orbital angular momentum (OAM) modes is promising, as they offer a high-dimensional and discrete Hilbert space to encode information. While entanglement by path identity with OAM has been verified experimentally, a detailed investigation of how the OAM distribution of photon pairs can be engineered to maximize the entanglement is lacking. We address this gap and identify an optimal dimensionality for maximally entangled states (MESs) when the spatial engineering of the pump beam and the path-identity approach are combined. Our theoretical study reveals notable limitations for the fidelity of high-dimensional target states. We also establish the equivalence of entangled biphoton states pumped by a spatially engineered beam and generated via path identity. These findings constitute a valuable step toward the optimized preparation of MESs in high dimensions.

We study the quantum nonlinear dynamics of multiple two-level atoms (qubits) in a waveguide quantum electrodynamics system, with a focus on modified superradiance effects between two or four atoms with finite delay times. Using a numerically exact matrix-product-states approach, we explore both Markovian and non-Markovian regimes and highlight the significant influence of time-delayed feedback effects and the clear breakdown of assuming instantaneous coupling dynamics. We first show a system composed of two spatially separated qubits, prepared in a doubly excited state (both fully excited), and provide a comprehensive study of how delayed feedback influences the collective system decay rates, as well as the quantum correlations between waveguide photons, atoms, and between atoms and photons. The system is then extended to include two additional qubits located next to the initial ones (four qubits in total), and we demonstrate, by manipulating the initial excitations and the time-delay effects, how long-term quantum correlations and light-matter entangled states can be established.

Nonlocality exhibited by ensembles of composite quantum states, wherein local operations and classical communication (LOCC) yield suboptimal discrimination probabilities compared to global strategies, is one of the striking nonclassical features of quantum theory. A variant of this phenomenon arises in conclusive local state discrimination, where the correct state must be identified with zero error, albeit allowing for inconclusive outcomes. More recently, the notion of local state marking has been introduced, with the focus shifted to correctly identifying the permutation of a subset of states randomly chosen from a given set of multipartite states under LOCC. In this work, we unify these two approaches by introducing the task of conclusive local state marking, which reveals a finer hierarchy of nonlocality in multipartite quantum state ensembles. Notably, we demonstrate that certain ensembles of product states can exhibit a stronger form of nonlocality than entangled ensembles traditionally considered highly nonlocal.

The quantum Fisher information (QFI) is a geometric measure of state deformation calculated along the trajectory parametrizing an ensemble of quantum states. It serves as a key concept in quantum metrology, where it is linked to the fundamental limit on the precision of the parameter that we estimate. However, the QFI is notoriously difficult to calculate due to its nonlinear mathematical form. For mixed states, standard numerical procedures based on eigendecomposition quickly become impractical with increasing system size. To overcome this limitation, we introduce a numerical approach based on Lyapunov integrals that combines the concept of symmetric logarithmic derivative and tensor networks. Importantly, this approach requires only the elementary matrix product states algorithm for time evolution, opening a perspective for broad usage and application to many-body systems. We discuss the advantages and limitations of our methodology through an illustrative example in quantum metrology, where the thermal state of the transverse-field Ising model is used to measure magnetic field amplitude.

Self-testing is a device-independent technique that allows for verification of unknown quantum systems only when observed correlations achieve some quantum supremum. In this paper, we present self-testing schemes for a class of multipartite Bell inequalities with a specific structure, which we refer to as the unit. Our research is based on the graph-theoretic approach, where correlations are characterized via Lovász theta body in the framework of exclusivity graphs. The derived statements are subsequently applied to prove the self-testability of $N$-partite Mermin-Ardehali-Belinskiǐ-Klyshko (MABK) family of Bell inequalities. In particular, we take special cases to demonstrate that the maximal violation of the multipartite MABK inequality is a self-test for the corresponding multipartite Greenberger-Horne-Zeilinger (GHZ) state. Moreover, we propose a device-independent verification algorithm for distributed blind quantum computation in the noisy intermediate-scale quantum era combined with multipartite GHZ state self-testing, where multiple quantum servers are involved and work in collaboration to reduce the burden on a single server.

Superconducting microwave resonators are used in many low-power applications, such as the study of two-level system loss in superconducting quantum devices. Fano asymmetry, characterized by a nonzero asymmetry angle $\varphi$ in the diameter correction method, results from the coupling schemes used to measure these devices, including the commonly used hanger method. $\varphi$ is an additional fitting parameter which contains no physically interesting information and can obscure device parameters of interest. The T-junction symmetry nominally present in these resonator devices provides an avenue for the elimination of Fano asymmetry using calibrated measurement. We show that the eigenvalue associated with the common mode excitation of the resonator is an effective reflection mode (ERM) which has no Fano asymmetry. Our analysis reveals the cause of Fano asymmetry as interference between common and differential modes. Practically, we obtain the ERM from a linear combination of calibrated reflection and transmission measurements. We utilize a three-dimensional aluminum cavity to experimentally demonstrate the validity and flexibility of this model. To extend the usefulness of this symmetry analysis, we apply perturbation theory to recover the ERM in a multiplexed coplanar waveguide resonator device and experimentally demonstrate quantitative agreement in the extracted $Q_i^{-1}$ between hanger mode and ERM measurements. We observe a fivefold reduction in uncertainty from the ERM compared to the standard hanger mode at the lowest measured power, −160 dBm delivered to the device. This method could facilitate an increase in throughput of low-power superconducting resonator measurements by up to a factor of 25, as well as allow the extraction of critical parameters from otherwise unfittable device data.

The inelastic processes in low-energy cation-anion lithium-hydrogen collisions are important for accurate determination of lithium abundances in late-type stars, which may be used in a variety of astrophysical phenomena such as Big Bang nucleosynthesis, stars and stellar cluster ages, as well as other stellar and laboratory plasma physics. For these reasons, the titled processes have been intensively treated by both theoretical and experimental methods, including the full-quantum stationary methods based on the numerical solution of the time-independent Schrödinger equation, the nonadiabatic models such as Landau-Zener model, the different experimental techniques, and so on. However, the full-quantum time-dependent approaches have not been employed so far. Since some discrepancies still remain and because of the importance of the titled processes, this paper is addressed to the wave-packet study of low-energy cation-anion lithium-hydrogen collisions, including participation of different hydrogen isotopes. In addition, we have modified the wave-packet method for better calculations of the inelastic transition probabilities.