Light-matter entanglement plays a fundamental role in many applications of quantum information science. Thus, finding processes where it can be observed is an important task. Here, using a one-dimensional model, we address this matter by investigating theoretically the entanglement between light and electrons generated in the above-threshold ionization (ATI) process. The study is based on the backaction of the ATI process on the quantum optical state of the system, and its dependence on the kinetic energy and direction of the emitted photoelectrons. Taking into account the dynamics of the process, we demonstrate the creation of hybrid entangled states. The amount of entanglement has been studied in terms of the entropy of entanglement. Additionally, we use the Wigner function of the driving field mode to motivate the entanglement characterization when considering electrons propagating in opposite directions.

After briefly reviewing Fujikawa's derivation of a chiral anomaly, we study fermions hopping on a lattice. Under the specific conditions considered in this paper, we show that a chiral gauge transformation induces a Berry's phase which is equal to Fujikawa's Jacobian.

We study four well-known capacities of a two-parameter family of qubit Pauli channels. These are the channels that are covariant under the $\text{SO}\left(2\right)$ group and contain the depolarizing channel as a special case. We find exact expressions for the classical capacity and entanglement-assisted capacities, and analytically determine the regions where the quantum capacity of the channel vanishes. We then use a flag extension to find upper bound for the quantum capacity and private capacity of these channels in the entire region of parameter space and also obtain the lower bound for the quantum capacity by calculating the single-shot quantum capacity numerically. In conjunction with previous results on depolarizing channels, our result is one step forward for determining the capacities of the full Pauli channel.

The multiparameter estimation in quantum metrology is significant for a large number of applications for quantum information tasks. Nevertheless, how mode correlations affect the multiparameter-estimation precision with and without photon-loss cases remains ambiguous. For this reason, here, we present the relationship between the quantum Cramér-Rao bound and the mode correlations in the framework of the simultaneous two-phase estimation for a three-mode Mach-Zehnder interferometer induced by the tritter which is composed of three cascaded beam splitters and phase shifters. By choosing different input resources, including a two-mode squeezed vacuum state $\otimes$ a coherent state (scheme I) and a twin squeezed vacuum state $\otimes$ a coherent state (scheme II), the results show that compared with scheme II, scheme I shows a better estimation performance even in the presence of photon losses. The reason may be that the intramode correlation of the probe state for scheme I is stronger than that for scheme II, while the intermode correlation of the probe state for the former is weaker than that for the latter. This allow us to open vital perspectives on the essence of enhanced multiparameter-estimation precision.

Certifying whether a photon Fock state is present or not while preserving its quantum state is an important task that proves useful in quantum technologies. The existing methods to perform such task apply to single photons only and consume costly quantum resources. In this paper, we propose a resource-efficient scheme for certification of an arbitrary (nonvacuum) photon Fock state by using second-order nonlinearity. In particular, we utilize the correlations in both photon number and polarization of a stimulated parametric downconversion process to herald the presence and the quantum state of an incoming Fock state. The proposed scheme works excellently with a near perfect certification fidelity even when using nonideal photodetectors. We then compare our scheme with the existing ones taking into account relevant figures of merit for each method. We also present applications of our scheme in overcoming transmission loss of photons in quantum channels as well as in preparation of NOON states, $\left(\right|N\rangle |0\rangle +|0\rangle |N\rangle )/\sqrt{2}$. Our paper introduces to the optical toolbox a practical technique that is beneficial for quantum communication and quantum metrology.

In this work, we consider the thermal correction to the hyperfine interaction in hydrogen, deuterium, and the ${}^3{\mathrm{He}}^{+}$ ion. This correction is effectively described by one-loop Feynman graphs in the framework of the quantum electrodynamics theory for bound states at a finite temperature. A simple analysis shows the importance of the obtained results for future prospects for measuring hyperfine splitting. In addition, the application for testing the time variation of fundamental constants is briefly discussed.

We theoretically investigate the collisional dynamics of laser-cooled ${}^{87}\text{Rb}$ ground-state atoms and ${}^{40}{\mathrm{Ca}}^{+}$ ground-state ions in the context of the hybrid trap experiment of Hall et al. [Phys. Rev. Lett. 107, 243202 (2011)], leading to ion losses. Cold ${}^{87}{\mathrm{Rb}}^{40}{\mathrm{Ca}}^{+}$ ground-state molecular ions are created by radiative association, and we demonstrate that they are protected against photodissociation by blackbody radiation and by the ${}^{40}{\mathrm{Ca}}^{+}$ cooling laser at 397 nm. This paper yields an interpretation of the direct observation of ${}^{87}{\mathrm{Rb}}^{40}{\mathrm{Ca}}^{+}$ ions in the experiment, in contrast to other hybrid trap experiments using other species. Based on an updated model for molecular spin-orbit interaction, we also confirm that the nonradiative charge-exchange is the dominant loss process for ${\mathrm{Ca}}^{+}$ and obtain rates in agreement with experimental observations and a previous calculation.

We examine the adiabatic preparation of spatially ordered Rydberg excitations of atoms in finite one-dimensional lattices by frequency-chirped laser pulses, as realized in a number of recent experiments simulating quantum Ising model. Our aims are to unravel the microscopic mechanism of the phase transition from the unexcited state of atoms to the antiferromagneticlike state of Rydberg excitations by traversing an extended gapless phase and to estimate the preparation fidelity of the target state in a moderately sized system amenable to detailed numerical analysis. We show that, despite its complexity, the interacting many-body system can be described as an effective two-level system involving a pair of lowest-energy instantaneous collective eigenstates of the time-dependent Hamiltonian. The final preparation fidelity of the target state can then be well approximated by the Landau-Zener formula, while the nonadiabatic population leakage during the passage can be estimated using a perturbative approach applied to the instantaneous collective eigenstates.

The formation of plasma waves during laser wakefield acceleration (LWFA) produces time-dependent frequency shifts in the driving laser pulse, extending its spectral content to the infrared. We present direct spectral measurements of multi-mJ infrared pulses from an LWFA. Experimental beam profile measurements and three-dimensional particle-in-cell simulations suggest high focusability of these pulses. Particle-in-cell simulations demonstrate that the measurement of side-scattered infrared radiation may serve as a diagnostic of plasma waves and the efficiency of spectral broadening during LWFA.

Quantum entanglement not only plays an important role in the study of the fundamentals of quantum theory, but also is considered as a crucial resource in quantum information science. The generation of macroscopic entanglement involving multiple optical and mechanical modes is a desired task in cavity optomechanics. However, the dark-mode effect is a critical obstacle against the generation of quantum entanglement in multimode optomechanical systems consisting of multiple degenerate or near-degenerate mechanical modes coupled to a common cavity mode. Here we propose an auxiliary-cavity-mode method to enhance optomechanical entanglement in a multimode optomechanical system by breaking the dark-mode effect. We find that the introduction of the auxiliary cavity mode not only assists the entanglement creation between the cavity mode and the mechanical modes, but also improves the immunity of the optomechanical entanglement to the thermal excitations by about three orders of magnitude. We also study the optomechanical entanglement in the network-coupled optomechanical system consisting of two mechanical modes and two cavity modes. By analyzing the correspondence between the optomechanical entanglement and the dark-mode effect, we find that optomechanical entanglement can be largely enhanced once the dark mode is broken. In addition, we study the mechanical entanglement and find that it is negligibly small. We also present some discussions on the experimental implementation with a microwave optomechanical setup, on the relationship between the dark-mode-breaking mechanism and the center-of-mass and relative coordinates, and on the explanation of the important role of the dark-mode breaking in the enhancement of optomechanical entanglement. Our results pave the way towards the preparation of entangled optomechanical networks and noise-resistant quantum resources.

The state-space structure for a composite quantum system is postulated among several mathematically consistent possibilities that are compatible with a local quantum description. For instance, the unentangled Gleason's theorem allows a state space that includes density operators as a proper subset among all possible composite states. However, bipartite correlations obtained in Bell-type experiments from this broader state space are, in fact, quantum simulable [Barnum et al., Phys. Rev. Lett. 104, 140401 (2010)], and hence, such spacelike correlations are no good for making a distinction among different compositions. In this work we analyze the communication utilities of these different composite models and show that they can lead to distinct utilities in a simple communication game involving two players. Our analysis thus establishes that a beyond quantum composite structure can lead to beyond quantum correlations in the timelike scenario and hence welcomes new principles to isolate the quantum correlations from the beyond quantum ones. We also prove a no-go theorem that the classical information carrying capacity of different such compositions cannot be greater than that of the corresponding quantum composite systems.

The dynamics of nonlinear flip-flop quantum walk with amplitude-dependent phase shifts with pertubing potential barrier is investigated. Through the adjustment between uniform local perturbations and a Kerr-like nonlinearity of the medium we find a rich set of dynamic profiles. We will show the existence of different Hadamard quantum walking regimes, including those with mobile soliton-like structures or self-trapped states. The latter is predominant for perturbations with amplitudes that tend to $\phi \to \pi /2$. In this system, the qubit shows an unusual behavior as we increase the amplitudes of the potential barriers and displays a monotonic decrease in the self-trapping ${\phi }_c$ with respect to the nonlinear parameter. A chaotic-like regime becomes predominant for intermediate nonlinearity values. Furthermore, we show that, by changing the quantum coins ($\theta$) a nontrivial dynamic arises, where coins close to Pauli-$X$ drives the system to a regime with predominant soliton-like structures, while the chaotic behavior are restricted to a narrow region in the $\chi -\phi$ plane. We believe that is possible to implement and observe the proprieties of this model in an integrated photonic system.

A precise estimation of the detection response is essential for a high-performance and secure quantum-key-distribution (QKD) system. Single-photon avalanche diodes (SPADs) are widely applied to estimate the single-photon yields. However, in the presence of the dead time and afterpulse of the SPADs, the estimations of gains in previous models are biased, which will lead to ill-fitting optimized parameters and greatly degrade the system performance. Here, we develop a dependency model for providing more accurate optimization to achieve higher-performance QKD systems. Moreover, to further improve the system performance, our model guides users to choose proper dead time. Our simulation results indicate that our model plays an important role in the practical application and deployment of QKD systems.

The energy shift in molecular spectra due to interaction of the nuclear magnetic quadrupole moment ($M$) with electrons is equal to $\delta E_M=M{W}_M{P}_M$ where $W_M$ is a constant determined by the electronic structure of the molecule and $P_M$ is a dimensionless constant. We extended the method for calculation of parity nonconservation effects in triatomic molecules developed in Ref. [A. Petrov and A. Zakharova, Phys. Rev. A 105, L050801 (2022)] to the case of $P_M$ constant and applied it to ${}^{173}\mathrm{YbOH}$ in the first excited $v=1$ bending mode. Results of our calculations are required for extraction of the $M$ value from the YbOH experiment.

We present a detailed analysis of the two-dimensional electron energy-loss spectrum of ${\mathrm{CO}}_2$, which extends our recent Letter [Phys. Rev. Lett. 129, 013401 (2022)]. We show that our vibronic coupling model [Phys. Rev. A 105, 062821 (2022)] captures primary features of the multidimensional dynamics of the temporary molecular anion, and the calculations qualitatively reproduce the spectrum. The shape of the spectrum is given by two overlapping contributions that originate in excitation of vibrational states within ${\mathrm{\Sigma }}_g^{+}$ and ${\mathrm{\Pi }}_u$ Fermi polyads. Propensity rules in terms of scattered and vibrational wave functions are also discussed to clarify the selectivity of states from the vibrational pseudocontinuum that is responsible for the observed fine structure.

We examine analytically and numerically the effect of fractionality on a saturable bulk and surface impurity embedded in a one-dimensional lattice. We use a fractional Laplacian introduced previously by us, and by the use of lattice Green functions we are able to obtain the bound state energies and amplitude profiles, as a function of the fractional exponent $s$ and saturable impurity strength $\chi$ for both surface and bulk impurity. The transmission is obtained in closed form as a function of $s$ and $\chi$, showing strong deviations from the standard case, at small fractional exponent values. The self-trapping of an initially localized excitation is qualitatively similar for the bulk and surface mode, but in all cases complete confinement is obtained at $s\to 0$, as shown theoretically and observed numerically.

We study the disentanglement dynamics of two giant atoms coupled to a common one-dimensional waveguide. We focus on the non-Markovian retarded effect in the disentanglement of the two giant atoms by taking the photon transmission time into account. By solving the time-delayed equations of motion for the probability amplitudes, we obtain the evolution of the entanglement of the two giant atoms, which are initially in the maximally entangled states in the single-excitation space. It is found that the retardation-induced non-Markovianity leads to nonexponential decay and revivals of entanglement. Concretely, we consider separate-, braided-, and nested-coupling configurations, and find that the disentanglement dynamics in these configurations exhibits different features. We demonstrate that the steady-state entanglement depends on the time delay under certain conditions in these three coupling configurations. We also study the dependence of the disentanglement of the two giant atoms on both the detuning effect and the initial-state phase effect. In addition, we consider the disentanglement dynamics of the two giant atoms, which are initially in the state superposed by zero-excitation and two-excitation components. This work will pave the way for the generation of stationary entanglement between two giant atoms, which may have potential applications in the construction of large-scale quantum networks based on the giant-atom waveguide-QED systems.