Spin polarization of the Auger electrons emitted from the nonradiative Auger decay $1s2s^{2}2p_{1/2}J=1\to 1s^{2}2s{J}_f=1/2+e_{\mathrm{A}}$ following inner-shell $1s$ photoionization of boronlike ions by circularly polarized light is studied using the multiconfigurational Dirac-Hartree-Fock method and the relativistic distorted-wave theory. Special attention is paid to the effect of the Breit interaction and also to the circular polarization transfer of the ionizing light to the spin polarization. The orientation and alignment parameters of the autoionizing level $1s2s^{2}2p_{1/2}J=1$ and the intrinsic anisotropy and spin polarization parameters of the Auger decay are calculated for boronlike ${\mathrm{Mg}}^{7+}, {\mathrm{Fe}}^{21+}, {\mathrm{Mo}}^{37+}, {\mathrm{Nd}}^{55+}, {\mathrm{Au}}^{74+}$, and ${\mathrm{U}}^{87+}$ ions. The transferred spin-polarization components $P_x$ and $P_z$ and the dynamic one $P_y$ of the Auger electrons are then obtained. The dynamic polarization $P_y$ is found to be much smaller than the transferred ones due to weak alignment of the autoionizing level. It is found that the Breit interaction hardly contributes to $P_x$, whereas the situation is much different for $P_z$. For medium- and high-$Z$ ions, for example, the transferred polarization $P_z$ is significantly enhanced by the Breit interaction for the Auger electrons emitted perpendicularly to the ionizing light beam but is weakened for those along the beam. Moreover, a quite strong circular polarization transfer of the ionizing light to the Auger electrons is found, which is comparable to the polarization transfer in the linear polarization of characteristic photons [Sharma et al., Phys. Rev. A 81, 023419 (2010)] but reveals evidence of the spin polarization of Auger electrons emitted from highly charged ions. Beyond the fundamental significance, the strong circular polarization transfer to the spin polarization of the Auger electrons enables a more detailed characterization of nonmagnetic systems, magnetically ordered materials, and (anti)ferromagnets at the atomic scale.

We report the experimental observation of ultrafast proton transfer in the $\mathrm{HCOOH}\text{−}{\mathrm{H}}_2\mathrm{O}$ complex following double ionization induced by a linearly polarized two-color femtosecond laser field with controlled relative phase. This process leads to the formation of ionic fragments ${\mathrm{H}}_3{\mathrm{O}}^{+}$ and $\mathrm{HCO}{\mathrm{O}}^{+}$, which are detected in coincidence. The measured anisotropic momentum distributions of the fragments reveal a preferential emission direction aligned with the laser polarization. Analysis of molecular orbitals and potential energy surfaces indicates that both electrons involved in the proton transfer process predominantly originate from the HCOOH moiety. Ab initio molecular dynamics simulations show that proton transfer is initiated promptly after ionization and completes within 100 fs. Furthermore, by tuning the relative phase of the two-color laser field, we demonstrate control over the emission direction of the ${\mathrm{H}}_3{\mathrm{O}}^{+}$ fragments. This directional emission is attributed to orientation-dependent tunneling ionization, as supported by simulations based on weak-field asymptotic theory.

The characteristic kinetic energies of electrons emitted in Auger decay processes of inner-vacancy states carries valuable information of the element and its chemical environment in atoms, molecules, clusters, liquids, and solids. Thus, Auger electron spectroscopy (AES) is widely used as an important experimental tool in both fundamental and applied research. In a dense plasma environment, however, the kinetic energies of Auger electrons are significantly modified and therefore AES shows new features compared with that of the isolated species. Here, we theoretically investigated the AES of K- and $2p$-vacancy states for different charge states of iron ions embedded in dense plasma. It is found that the kinetic energy of the Auger electron is evidently shifted toward higher energy compared with the isolated ion; The higher the mass density and ionization stage, the larger shift the kinetic energy of the Auger electron. The shift of kinetic energy of the Auger electron is also weakly temperature dependent with a lower shift at a higher temperature of the plasma. The Auger widths of the $2p$-vacancy states are more evidently affected by the plasma environment than the K-vacancy states, especially at a higher plasma density. The findings of the present work are helpful for the study of Auger processes and radiative properties in dense plasmas such as astrophysical plasmas in the interior of stars and laboratory plasmas produced in interaction of x-ray free-electron lasers with solids, liquids, nanoplasmas, and clusters.

We predict and experimentally demonstrate a type of collective (cooperative) coupling effect where a disordered atomic ensemble absorbs light with a rise time longer (i.e., at a rate slower) than what is dictated by single-atom physics. This effect, which we name subabsorption, can be viewed as the absorptive analog of subradiance. The experiment is performed using a dilute ensemble of ultracold ${}^{87}\mathrm{Rb}$ atoms with a low optical depth, and time resolving the absorption of a weak (tens of photons per pulse) resonant laser beam. In this dilute regime, the collective interaction relies on establishing dipole-dipole correlations over many atoms; i.e., the interaction is not dominated by the nearest neighbors. As a result, subabsorption is highly susceptible to motional dephasing: even a temperature increase of $60\mu \mathrm{K}$ is enough to completely extinguish the subabsorption signal. We also present a theoretical model whose results are in reasonable agreement with the experimental observations. The model uses the density-dependent dephasing rate of the long-range dipole-dipole correlations as a single adjustable parameter. Experiment-theory comparison indicates a dephasing coefficient of $\beta /2\pi =4.9\times {10}^{-5}\mathrm{Hz}{\mathrm{cm}}^3$, which is more than two orders of magnitude larger than the known dipole-dipole line broadening coefficient in ${}^{87}\mathrm{Rb}$.

Ultrahigh-intensity laser-matter interactions generate high-energy photons, which carry essential information about the dynamics in the interaction region. Several models are developed to describe the statistical properties of emitted photons and the total photon yield produced by an electron beam propagating through a static, homogeneous magnetic field. The accuracy of these models, as well as the Fokker-Planck approximation, is verified using first-principles Monte Carlo simulations. While these models are valid in the quasiclassical regime, it is demonstrated that a model can be constructed to describe photon statistics in both the quasiclassical and quantum regimes. The extension of the developed approach to the strong quantum regime is discussed. Finally, the results are generalized to the case of an electron beam interacting with an ultrashort, high-intensity laser pulse.

The quantum battery (QB) is a conceptually new energy storage and conversion device, which consists usually of a quantum charger and an energy store (usually called the QB for simplicity). The demonstrated advantage of a QB, over its classical counterpart, is that its charging efficiency can be significantly enhanced by using quantum entanglement resources. In this paper, we investigate alternatively how to realize the switchable charging and the lossless power detection of the charged QB. With the proposed QB configuration we show that, by adjusting the eigenfrequency of the qubit-based charger, the cavity-based QB can be switched on between the charging and power-off states and its stored energy can be nondestructively monitored by probing the transmitted spectrum of the external electromagnetic waves scattered by the qubit-based charger. As the qubit-based charger has never been excited, the proposed cavity-based QB could directly store the coherent-state energy (rather than the single-photon one) and thus possess significantly large ergotropy. The physical realization of the proposed switchable QB configuration is demonstrated specifically with the experimental circuit quantum electrodynamical devices.

We establish limitations and bounds on the transmission of quantum states between gravitationally interacting mechanical oscillators under different models of gravity. This provides benchmarks that can enable tests for quantum features of gravity. Our proposal does not require the measurement of gravitationally induced entanglement and only requires final measurements of a single subsystem. We discuss bounds for classical models based on local operations and classical communication when considering coherent-state alphabets, and we discuss the transfer of quantum squeezing for falsifying the Schrödinger-Newton model.

Understanding how noise degrades entanglement is crucial for the development of reliable quantum technologies. While the Markovian approximation simplifies the analysis of noise, it remains computationally demanding, particularly for high-dimensional systems like quantum memories. In this paper, we present a statistical approach to study the impact of different noise models on entanglement in composite quantum systems. By comparing global and local noise scenarios, we quantify entanglement degradation using the positive partial transpose time (PPTT) metric, which measures how long entanglement persists under noise. When the sampling of different noise scenarios is performed under controlled and homogeneous conditions, our analysis reveals that systems subjected to global noise tend to exhibit longer PPTTs, whereas those influenced by independent local noise models display the shortest entanglement persistence. To carry out this analysis, we employ a computational method proposed by Cao and Lu, which accelerates the simulation of PPTT distributions and enables efficient analysis of systems with dimensions up to $D=8$. Our results demonstrate the effectiveness of this approach for investigating the resilience of quantum systems under Markovian noise.

Error correction is generally demanded in large-scale quantum information processing and quantum computation. We provide here a universal and real-time control strategy to dynamically correct the arbitrary type of errors in the system Hamiltonian. It yields multiple error-resilient paths for the interested system which are activated by the von Neumann equation for ancillary projection operators. With no extra control fields and precise designs, the path-dependent global phase alone suffices to mitigate the error-induced transitions among distinct paths as long as it varies faster than the other parameters. The corrected paths can also be regarded as the approximate solutions to the time-dependent Schrödinger equation perturbed by errors. Our dynamical-correction strategy is practiced with the cyclic transfer of populations in a three-level system, showing a superior error resilience to the parallel-transport condition. It provides a promising idea for advancing control methodologies in imprecise quantum systems.

We propose a method to deterministically entangle qubits or ensembles of qubits interacting with a shared bosonic mode in the ultrastrong coupling regime. We show that the resulting gate is a product of two unitaries: one unitary acts only on the quantum state of the qubits and entangles them, while the other acts only on the quantum state of the boson, producing a phase shift. We find that the gate time is inversely proportional to the qubit-boson interaction strength, and by tuning the qubit-boson interaction strength, one can prepare a maximally entangled state or a squeezed state. Applying the quantum gate to multiple qubit ensembles, we show that the quantum gate prepares a Schrödinger cat state. We also examine imperfections such as including free evolution of the qubits and show that this produces an effective mixing. Our proposal is feasible for ultrastrong coupling experiments.

We study a one-dimensional three-component Fermi gas with population imbalance using the Bogoliubov–de Gennes mean-field approach. We specifically consider pairing in two channels while deliberately excluding the third by setting its interaction strength to zero. By systematically varying the interaction strength and population imbalance, we identify a rich set of spatially modulated superfluid states, including structures akin to the Larkin-Ovchinnikov phase and phase-separated domains. A clear hierarchy emerges in the pairing behavior, shaped by the competition between the local density of states and the Fermi-momentum mismatch. A fidelity-based analysis of the density further distinguishes smooth crossovers from sharp spatial reorganizations. Our results shed light on how pairing symmetry and population imbalance determine the structure of spatially inhomogeneous superfluid phases in multicomponent systems with reduced dimensionality.

Our experiments on focusing of ultraviolet $\sim 250\text{−}\mathrm{nm}, \sim 100\text{−}\mathrm{fs}$, 0.2-mJ pulses into a cuvette filled with diatomic air or monatomic argon show similar spectral transformations regardless of the gas if the pressure is the same. The spectra experience broadening and the long-wavelength shift, which increases monotonically with the pressure and reaches 2 nm at 1 atm. This long-wavelength shift cannot be explained by instantaneous Kerr nonlinear response and multiphoton ionization as two additive contributions to the nonlinear refractive index. The simulations based on the 1D time-dependent Schrödinger equation reveal that the cubic nonlinearity is delayed by $\sim 100$ as with regard to the driving field. This intraperiod delay comparable with the $\sim 800\text{−}\mathrm{as}$ field cycle shifts the polarization spectrum to longer wavelengths and can be obtained solely from the quantum-mechanical approach, which we uniquely applied to the description of ultraviolet femtosecond filamentation.

We investigate the application of the Sturmian basis set to relativistic atomic structure calculations. We propose a simple implementation of this approach and demonstrate its ability to provide various quantities for hydrogenlike ions, including binding energies, static dipole polarizability, the $g$ factor, hyperfine splitting, and nuclear magnetic shielding. Finally, we calculate the all-order (Wichmann-Kroll) vacuum-polarization charge density, which was a challenge for the finite-basis-set approach until recently. We present a comparison of the obtained results with previously published numerical and analytical calculations. All calculations are performed with nuclei of a finite size and can, in principle, be extended to arbitrary binding potentials.

We theoretically study atomic laser-assisted photoelectric emission (LAPE) beyond the electric dipole approximation. We present a theoretical description based on the strong-field approximation (SFA) for first-order nondipole corrections $[O\left(c^{-1}\right)$, where $c$ is the speed of light] to the nonrelativistic description of the laser-atom interaction for a strong circularly polarized IR laser field combined with a train of extreme-ultraviolet pulses. We investigate the photoelectron momentum distribution (PMD) as the product of two main contributions: the intra- and interpulse factors. Whereas the interpulse factor gives rise to a sideband pattern with a shift opposite to the IR beam propagation direction, the intrapulse factor forms an angular streaking pattern following the IR time-dependent polarization direction. We explore the transition of the PMD from the dipole to the nondipole framework, showing the gradual break of the forward-backward symmetry as the laser parameters are varied. Furthermore, we find nonzero contributions in dipole forbidden directions independent of the IR polarization state, wherein Cooper-like minima are observed. Our work lays a theoretical foundation for understanding time-resolved nondipole LAPE in cutting-edge ultrafast experiments.

A novel solid-gas dual-target configuration is employed to investigate the process of ultraviolet-assisted high harmonic generation (HHG) in gases. A distinct phenomenon of spectral splitting and bandwidth widening was observed in the experiment. The theoretical simulations are in good agreement with the experimental results, confirming the selective enhancement of long trajectory contributions in HHG under this experimental configuration. Once a delay control element is added, our scheme has the potential to precisely enhance different quantum path in HHG.

Optical time delays play a pivotal role in modern physics and practical applications. We propose and experimentally validate a weak measurement system with a double-edge filter, which enables the real-time, high-precision estimation of varying time delays, and the effective suppression of technical noise. In the experiment, the postselected probe light is processed by the double-edge filter, which is formed by a pair of fiber Bragg gratings positioned symmetrically about the center frequency of the probe light, and subsequently detected by photodetectors. The experimental results demonstrate a time-delay precision of 1.66 attoseconds (as) and real-time estimation capability. With a postselection angle of ${10}^{-3}\mathrm{rad}$ and the system operating within the most sensitive linear dynamic range, the precision can be further improved to ${10}^{-4}$ as. The approach benefits from its high sensitivity and rapid detection, which shows great potential applications in real-time and high-precision time-delay measurements.

The optical force density acting in transparent dielectric media due to short laser excitation is theoretically analyzed. For typical laser pulses with picosecond duration, the momentum component of the optical force becomes of the same order of magnitude as the stress component, enhancing the overall optomechanical effects. Simulations of the optically induced surface displacements in fused silica glass are also presented. With careful choice of realistic simulation parameters, dispersive and nonlinear effects were shown to be suppressed and displacements of 50 pm were found for single-pulse excitation with 100-fs duration, where the momentum component of the force is dominant. A possibility of measuring these displacements with piezoelectric detection is also discussed, providing a way to attain spatiotemporal characterization of the optical momentum force in continuum media. Such a description would significantly advance our current knowledge of the behavior of optical forces, potentially contributing to more versatile optomechanical applications while also clarifying the ongoing Abraham-Minkowski fundamental problem on the momentum transferred by light.

We introduce a framework that allows for the exact analytic treatment of quantum dynamics subject to noise, captured by unitary evolution under a Hamiltonian drawn from a random-matrix ensemble. The unitary acts on a Hilbert space of arbitrary dimension $N$, which may include ancillary (e.g., “bath”) degrees of freedom, and the “strength” of the noise is tunable. While the methods we develop apply to generic random-matrix ensembles with a notion of rotation invariance, we explicitly consider the Gaussian unitary ensemble (GUE). Averaging over the ensemble of “noisy” Hamiltonians produces an effective quantum channel, the properties of which are analytically calculable and determined by the spectral form factors of the relevant ensemble. We compute spectral form factors of the GUE exactly for any finite $N$, along with the corresponding GUE quantum channel and its variance. Importantly, the GUE channel captures the effects of generic unitary sources of noise. Key advantages of our approach include the ability to access exact analytic results for any $N$, the ability to tune to the noise-free limit (in contrast, e.g., to the Haar ensemble), and analytic access to moments beyond the variance. We also highlight some unusual features of the GUE channel, including the nonmonotonicity of the coefficients of various operators as a function of noise strength and the failure to saturate the Haar-random limit, even with infinite noise strength.