We study the monogamy of arbitrary quantum entanglement measures $E$ for tripartite quantum systems. Both the sufficient and necessary conditions for $E$ to be monogamous in terms of the $\alpha \mathrm{th}$ power of $E$ are explicitly derived. It is shown that such monogamy of an entanglement measure $E$ only depends on the boundedness of the solution set of certain equations. Moreover, the monogamy conditions are also obtained with respect to certain subsets of quantum states for a given quantum correlation. Detailed examples are given to illustrate our results.

Alignment dephasing caused by centrifugal distortion is a significant effect accompanying laser-induced field-free molecular alignment. Centrifugal distortion is the manifestation of the intrinsic nonrigidity of molecules, which is especially prominent when molecules are excited to high angular velocities. In this work, we show that this type of dephasing can be almost completely eliminated by modulating the phase of the femtosecond laser pulse. Nearly perfect molecular alignment can be achieved as if the molecules were ideal rigid rotors. The dephasing effect can be cancelled in various time windows by tuning the modulation strength parameter. The dephasing cancellation mechanism is explained by considering the relative phases of the eigenstates forming the rotational wave packet. This work is of great significance to the experiment and dynamics studies of molecular alignment.

The emergent phases of strongly correlated spin-$\frac{1}{2}$ Fermi gases of Rydberg-dressed atoms in a one-dimensional optical lattice are theoretically investigated. At weak coupling a bosonization description is used to demonstrate the ability to drive alternating quantum phase transitions between distinct Luttinger liquids. At strong coupling the ground state develops nontrivial phase separation exhibiting Luttinger liquid “puddles” separated by magnetic domain walls due to the interplay of the incommensurate filling and the Rydberg core length scale. These phases can be detected in ultracold gases of Rydberg atoms made from ${}^6\mathrm{Li}$.

${}^{23}\mathrm{Na}$ spin-1 Bose-Einstein condensates are used to experimentally demonstrate that mean-field physics beyond the single-mode approximation can be relevant during the nonequilibrium dynamics. The experimentally observed spin oscillation dynamics and associated dynamical spatial structure formation confirm theoretical predictions that are derived by solving a set of coupled mean-field Gross-Pitaevskii equations [J. Jie et al., Phys. Rev. A 102, 023324 (2020)]. The experiments rely on microwave dressing of the $f=1$ hyperfine states, where $f$ denotes the total angular momentum of the ${}^{23}\mathrm{Na}$ atom. The fact that physics beyond the single-mode approximation at the mean-field level, i.e., spatial mean-field dynamics that distinguishes the spatial density profiles associated with different Zeeman levels, can, in certain parameter regimes, have a pronounced effect on the dynamics when the spin healing length is comparable to or larger than the size of the Bose-Einstein condensate has implications for using Bose-Einstein condensates as models for quantum phase transitions and spin squeezing studies as well as for nonlinear SU(1,1) interferometers.

We theoretically investigate three-body losses in a single-component Fermi gas near a $p$-wave Feshbach resonance in the interacting, nonunitary regime. We extend the cascade model introduced by Waseem et al. [M. Waseem, J. Yoshida, T. Saito, and T. Mukaiyama, Phys. Rev. A 99, 052704 (2019)] to describe the elastic and inelastic collision processes. We find that the loss behavior exhibits a $n^3$ and an anomalous $n^2$ density dependence for a ratio of elastic-to-inelastic collision rate larger and smaller than 1, respectively. The corresponding evolutions of the energy distribution show collisional cooling or evolution toward low-energetic nonthermalized steady states, respectively. These findings are particularly relevant for understanding atom loss and the energetic evolution of ultracold gases of fermionic lithium atoms in their ground state.

The non-Hermitian skin effect (NHSE), which involves an extensive number of bulk modes collapsing to open boundaries as skin modes, unveils a variety of unprecedented topological physics. However, achieving this effect in photonic waveguides has been challenging due to the difficulty of establishing the required non-Hermitian asymmetric couplings. Here, we investigate NHSE in photonic waveguide arrays via Floquet engineering. By periodically driving the waveguides along the propagation direction, we create an artificial gauge field (AGF) that interacts with on-site dissipation, yielding non-Hermitian asymmetric coupling and eventually giving rise to NHSE. The localization direction of NHSE is tunable by AGFs and can be detected from light propagation. In particular, we explore the interplay between NHSE and dynamical localization, whereby NHSE is suppressed by dynamical localization due to the collapse of quasienergies. Our proposed method can be extended to explore the non-Bloch Su-Schrieffer–Heeger model, with potential implications for steering light transport with the aid of NHSE.

We present a theoretical framework based on second quantization in Liouville space to treat open quantum systems. We consider an ensemble of identical quantum emitters characterized by a discrete set of quantum states. The second quantization is performed directly at the level of density matrices, thereby significantly reducing the size of the Liouville space. In contrast to conventional Hilbert space techniques, statistically mixed states and dissipation are naturally incorporated. As a particular example of application, we study the effect of incoherent processes and statistical mixing of emitters initial states in the interaction with quantum light. Moreover, we link our framework to a phase-space description of the dynamics, which can overcome the computational limitations of our method with the increasing number of particles.

In a quantum many-body system coupled to the environment, its steady state can exhibit spontaneous symmetry breaking when a control parameter exceeds a critical value. In this study, we consider spontaneous symmetry breaking in nonsteady modes of an open quantum many-body system. Assuming that the time evolution of the density matrix of the system is described by a Markovian master equation, the dynamics of the system is fully characterized by the eigenmodes and spectrum of the corresponding time evolution superoperator. Among the nonsteady eigenmodes with finite lifetimes, we focus on the eigenmodes with the highest frequency, which we call the most coherent mode. For a dissipative spin model, it is shown that the most coherent mode exhibits a transition from a disordered phase to a symmetry-broken ordered phase, even if the steady state does not show singular behavior. We further argue that the phase transition of the most coherent mode induces a qualitative change in the decoherence dynamics of highly entangled states, i.e., the Schrödinger's cat states.

The 16-component, no-pair Dirac–Coulomb–Breit equation, derived from the Bethe–Salpeter equation, is solved in a variational procedure using Gaussian-type basis functions for the example of positronium, muonium, hydrogen atom, and muonic hydrogen. The $\alpha$ fine-structure-constant dependence of the variational energies, through fitting a function of ${\alpha }^n$ and ${\alpha }^{n}ln\alpha$ terms, shows excellent agreement with the relevant energy expressions of the (perturbative) nonrelativistic QED framework and thereby establishes a solid reference for the development of a computational relativistic QED approach.

Coulomb confinement resonances (CCRs) are the main features of the photoionization spectra of an atom inside an anionic fullerene. These CCRs can act as an amplifier to spin-orbit-interaction-activated interchannel coupling (SOIAIC) and can lead to discernible signatures of relativistic effects even for low $Z$ confined atomic systems. The present paper demonstrates this intriguing feature by studying angular photoemission time delay of the $2p_{3/2}$ subshell of $\mathrm{Ar}@{\mathrm{C}}_{60}^{-1}$ in the vicinity of the $2p_{1/2}$ ionization threshold. Here $2p_{1/2}$ CCR functions as an amplifier to the SOIAIC and, thereby, induces significant modifications in the $2p_{3/2}$ angular time delay through the interchannel coupling. Moreover, the effects of the SOIAIC for the spin-up and spin-down photoelectrons are found to be different. All of these suggest that angle-resolved time-delay measurements can reveal the relativistic effects even for the low Z confined atomic systems, and $\mathrm{Ar}@{\mathrm{C}}_{60}^{-1}$ is a potential candidate for such experimental scrutiny. The impact of the model parameters on the predicted feature is also critically examined by using different sets of parameters. All of those calculations showed the existence of SOIAIC enabled structures in the angular time-delay profile.

We present a theoretical study of atomic laser-assisted photoionization emission beyond the dipole approximation. By considering the nonrelativistic nondipole strong-field approximation (nondipole Gordon-Volkov wave function), we analyze the different contributions to the photoelectron spectrum, which can be written in terms of intra- and intercycle factors. We find that our nondipole approach not only exhibits asymmetric emission in the direction of light propagation, but also allows emission in dipole-forbidden directions. The former feature can be rooted in both intra- and intercycle interference processes, while the latter stems from a dependence of the sideband energy on the emission angle with respect to the propagation direction. Our theoretical scheme, presented here for He atoms in the $1s$ quantum state, is general enough to be applied to other atomic species and field configurations.

The Faraday rotation and ellipticity spectra of rubidium $5P_{3/2}\to 4D_{5/2}$ transition in a magnetic field have been calculated and experimentally measured. By using the rotating quarter-wave plate method, the Stokes parameters of the $5P_{3/2}\to 4D_{5/2}$ near-resonant probe light are measured to obtain the Faraday rotation and the ellipticity. The variation of the rotation and the ellipticity spectra is analyzed in different magnetic fields, temperatures, and pump powers. The polarization rotation over 50 deg in 1529 nm with negligible elliptical distortion is obtained. Our study of the Faraday effect between excited states of atoms broadens the available wavelength of the Faraday effect in applications.

Absorption and emission of light is studied theoretically for excited atoms in coherent superposition of states subjected to isolated attosecond pulses in the extreme ultraviolet range. A gauge-invariant formulation of transient absorption theory is motivated using the energy operator from Yang's gauge theory. The interaction, which simultaneously couples both bound and continuum states, is simulated by solving the time-dependent Schrödinger equation for hydrogen and neon atoms. A strong dependence on the angular momentum and the relative phase of the states in the superposition is observed. Perturbation theory is used to disentangle the fundamental absorption processes and a rule is established to interpret the complex absorption behavior. It is found that nonresonant transitions are the source of asymmetry in energy and phase, while resonant transitions to the continuum contribute symmetrically to absorption of light from coherent superpositions of states.

We simulate the two-dimensional high-energy photoelectron momentum distributions (PMDs) for high-order above threshold ionization (HATI) of hydrogen atoms in intense elliptically polarized laser fields by using the strong-field approximation and solving the time-dependent Schrödinger equation. It is found that the centers of the left- and right-side circular rescattered ridges in the PMDs due to elastic collision of the returning electron with the parent ion, that locate on the polarization axis for linearly polarized laser field, move slightly below and above the major polarization axis, respectively, for elliptically polarized laser fields. We suggest that, by analyzing the center shift of the measured PMDs for HATI in elliptically polarized fields, one can identify the recollision time.

We discuss the work done on repulsive ultracold Fermi gas via collisions tuned by a time-dependent magnetic ramp. If the interaction is strengthened during binary collisions, the kinetic energy of atoms increases with each such inelastic event. The net energy transfer via collisions is compared with the transfer via the mean field. It is found that for a weak interaction, with a scattering length shorter than the inverse mean momentum of atoms, the mean field dominates, while for a strong interaction, the majority of energy enters the gas via collisions.

Using the generalized nonlinear Schrödinger equation, we investigate how the effect of self-steepening and Raman-induced self-frequency shift impact higher-order rogue-wave solutions. We observe that each effect breaks apart the higher-order rogue wave, reducing it to its constituent fundamental parts, in a similar manner to how a higher-order soliton undergoes fission. Applying a local inverse-scattering technique, we show that under the effect of self-frequency shift, the emergence of a rogue wave significantly influences the surrounding wave background, triggering solitons, breathers, and new rogue waves. We demonstrate that under the combined effect of third-order dispersion, self-steepening, and Raman-induced self-frequency shift, the disintegrated elements of higher-order rogue waves become fundamental solitons, creating an asymmetrical spectral profile that generates both red- and blue-shifted frequency components. We also show the intermediary processes of the fission steps prior to soliton transformation which can only be observed in the presence of weak perturbations. These observations reveal the mechanisms that create a large number of solitons in the process of modulation instability-induced supercontinuum generation from a continuous-wave background in optical fibers.

The phase-space quasiprobability distribution formalism for representing quantum states provides practical tools for various applications in quantum optics such as identifying the nonclassicality of quantum states. We study filter functions that are introduced to regularize the Glauber-Sudarshan $P$ function. We show that the quantum map associated with a filter function is completely positive and trace preserving and hence physically realizable if and only if the Fourier transform of this function is a probability density distribution. We also derive a lower bound on the fidelity between the input and output states of a physical quantum filtering map. Therefore, based on these results, we show that any quantum state can be approximated, to arbitrary accuracy, by a quantum state with a regular Glauber-Sudarshan $P$ function. We propose applications of our results for estimating the output state of an unknown quantum process and estimating the outcome probabilities of quantum measurements.

Under a perpendicular magnetic field, electrons in two-dimensional disks occupy quantum-confined Landau levels. By analyzing the electric polarizability of such states, we reveal an extreme sensitivity to confinement. Hence, an exponential increase with magnetic field or disk size is found and ascribed to the linear Zeeman effect. In contrast, if the balance between linear and quadratic Zeeman terms is slightly reduced, due to, e.g., addition of a nonmagnetic parabolic potential, the polarizability varies nonmonotonically with field strength and eventually vanishes. The analysis is based on a compact exact expression for the polarizability valid for arbitrary magnetic field, disk size, and linear Zeeman strength.