An atom, coupled linearly to an environment, is considered in a harmonic approximation in thermal equilibrium inside a cavity. The environment is modeled by an infinite set of harmonic oscillators. We employ the notion of dressed states to investigate the time evolution of the atom initially in the first excited level. In a very large cavity (free space) for a long elapsed time, the atom decays and the value of its occupation number is the physically expected one at a given temperature. For a small cavity the excited atom never completely decays and the stability rate depends on temperature.

We disclose the behavior of quantum and classical correlations among all the different spatial-temporal regions of a space-time with an event horizon, comparing fermionic with bosonic fields. We show the emergence of conservation laws for entanglement and classical correlations, pointing out the crucial role that statistics plays in the information exchange (and more specifically, the entanglement tradeoff) across horizons. The results obtained here could shed new light on the problem of information behavior in noninertial frames and in the presence of horizons, giving better insight into the black-hole information paradox.

Four-component relativistic coupled-cluster calculations including the nuclear spin-free electroweak field are presented for the chiral molecule CHFClBr using a finite-field method to obtain accurate electron correlation effects for the parity-violation energy shift in CHFClBr. The results are used to obtain optimal parameters for the Coulomb-attenuated Becke three-parameter Lee-Yang-Parr hybrid functional (CAM-B3LYP), which is useful for future applications in this field.

The first Born approximation is examined for different fast capture processes for the $p+\mathrm{He}$ system at incident energies of about 1 MeV. Calculations have been performed for the singly differential cross section (SDCS) for scattering angles 0–0.5 mrad in the laboratory frame. In the case of transfer ionization, we observe that the two-step-2 mechanism has a dominant contribution to the SDCS for the kinematics considered in this work. The present investigation demonstrates that the multiple peaking approximation is a very crude method which fails to describe the SDCS even at scattering angles below 0.5 mrad. We have also presented a doubly differential cross section for the fixed emission energy of 600 eV and compared our results with other theoretical calculations and experiments.

Double ionization of isolated water molecules fixed in space is here investigated in a theoretical approach based on the first Born approximation. Secondary electron angular distributions are reported for particular ($e,3e$) kinematical conditions and compared in terms of shape and magnitude. Strong dependence of the fivefold differential cross sections on the molecular target orientation is clearly observed in ($e,3-1e$) as well as ($e,3e$) channels. Furthermore, for the major part of the kinematics considered, we identified the different mechanisms involved in the double ionization of water molecule, namely, the direct shake-off process as well as the two-step1 process. They are both discussed and analyzed with respect to the molecular target orientation.

The ionization dynamics of slow hydrogenlike Rydberg atoms (principal quantum number $n\gg 1$) approaching solid surfaces is considered via an ion-collection electric field, using an appropriate etalon equation method. The complex energy eigenvalue problem is solved in the critical region $R\approx R_c\approx R_c^I$ of the ion-surface distances $R$ in which the ionization process is mainly localized and the parabolic symmetry is preserved. The relatively simple analytical forms for the parabolic rates enable us to elucidate the main features of the self-consistent ionization dynamics of the projectiles with the time-dependent charges. The ionization distances $R_c^I$ are calculated and an agreement of the averaged probability (for the atomic beam) with the corresponding experimental results is discussed for the relevant parameters of the ion-surface system. The formulas are suggested for the simulation of the experimental signal and for deducing the $R_c^I$ values from this signal.

As a first step toward the adiabatic theory of ionization of atoms by intense few-cycle laser pulses, here we consider the simplest one-dimensional zero-range-potential model. The theory for this model is developed. This theory rests on a single parameter $\epsilon$ giving a ratio of the atomic and laser time scales and becomes exact in the limit $\epsilon \to 0$ uniformly with respect to the amplitude of the laser pulse. We construct the asymptotics of the solution to the time-dependent Schrödinger equation and photoelectron spectrum. The factorization formula for the photoelectron spectrum near its classical boundary, first suggested by T. Morishita et al. [Phys. Rev. Lett. 100, 013903 (2008)] on the basis of ab initio calculations, is derived. The theory is illustrated by numerical calculations. Its comparison with the strong-field approximation is discussed.

Single-active-electron potentials are computed for selected molecules, and molecular wave functions with the correct asymptotic behavior are produced. Asymptotic expansion coefficients are extracted from the wave functions and used to compute alignment-dependent ionization yields from molecular tunneling theory. The predictions of molecular tunneling theory are benchmarked by ab initio calculations based on the solution of the time-dependent Schrödinger equation within the single-active-electron approximation.

We apply a previously developed semiclassical complex time method to the calculation of tunneling ionization of several diatomic molecules and CO${}_2$. We investigate the presence or absence of the molecular suppression effect by calculating ionization rates of ${\mathrm{N}}_2$ versus Ar, ${\mathrm{O}}_2$ versus Xe, ${\mathrm{F}}_2$ versus Ar, and CO versus Kr. Comparisons with other theories, including the molecular-orbital-Ammosov-Delone-Krainov (MO-ADK) model and the strong-field approximation, are given. We also analyze the dependence of the ionization rate on the angle ${\theta }_F$ between the molecular axis and the field direction. The theoretical results agree quite well with experiment for ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ but give too low a value of the peak angle ${\theta }_F$ for CO${}_2$. Our calculations give small values of the ionization rates for ${\mathrm{O}}_2$ and CO${}_2$ at ${\theta }_F=0$ and ${90}^{°}$, in agreement with experiment. Other calculations, including the MO-ADK model and methods involving a numerical integration of the time-dependent Schrödinger equation, exhibit substantially weaker suppression at these angles.

We study the time dependence of the spectrum of inelastically scattered radiation from a trapped atom. The atom is illuminated by two lasers tuned to the electromagnetically induced transparency (EIT) of the free atom. For counterpropagating laser beams, rapid removal of vibrational energy is observed as the atom approaches near-EIT conditions. We show that the imbalance in the sidebands of the scattered radiation spectrum explains quantitatively the cooling of the center-of-mass motion of the trapped atom. We also examine parameters critical for EIT cooling in situations far from the Lamb-Dicke limit.

The polarization and relaxation rates of metastable ${}^{129}\mathrm{Xe}$ atoms are measured with magnetic resonance spectroscopy, at both microwave frequencies, where $\Delta F=1$ transitions are induced between the sublevels, and at radiofrequencies, corresponding to $\Delta F=0$ transitions. The nuclear spin polarization of the resonant velocity group is measured to be $22\pm 2\%$. The relaxation of metastable xenon atoms is dominated by depolarizing collisions with ground-state atoms, with lesser contributions from metastability exchange collisions.

Nonlinear Schrödinger (NLS) equation with external potentials (lattices) possessing crystal and quasicrystal structures are studied. The fundamental solitons and band gaps are computed using a spectral fixed-point numerical scheme. Nonlinear and linear stability properties of the fundamental solitons are investigated by direct simulations and the linear stability properties of the fundamental solitons are confirmed by analysis the linearized eigenvalue problem.

We propose, analyze, and study numerically a phase shifter for light wave packets trapped by Kerr solitons in a nonlinear medium. We also study numerically a previously proposed soliton-guided nonpolarizing beam splitter.

We show that it is possible to obtain continuous variable entanglement for four optical fields via phase-dependent electromagnetically induced transparency in a four-level system in double-$\Lambda$ configuration. Due to quantum interference, the four fields constitute two quantum beats, behave as a pair of collective modes, and experience high cross Kerr nonlinearities. As a result, entanglement occurs between the two collective modes and between any two individual fields from the different collective modes.

By taking advantage of a conformal mapping technique, we propose designs for various optical elements such as directional antennas, flat lenses, or bends. In contrast to most of the existing design approaches, the elements can be implemented with isotropic materials, thus strongly facilitating their fabrication. We furthermore generalize the concept and show that under certain conditions previously suggested devices consisting of anisotropic materials may be replaced by isotropic ones using an appropriate transformation. The designs are double-checked by full-wave simulations. A comparison with their anisotropic counterparts reveals a similar performance.

We show that the anisotropy of the recoil velocity distribution of x-ray-ionized atoms or molecules leads to observable splittings in subsequent optical fluorescence or absorption when the polarization vector of the x rays is parallel to the momentum of the fluorescent photons. The order of the magnitude of the recoil-induced splitting is about 10 $\mu$eV, which can be observed using Fourier or laser-absorption spectroscopic techniques.

The parameters of a nondegenerate quantum code must obey the Hamming bound. An important open problem in quantum coding theory is whether the parameters of a degenerate quantum code can violate this bound for nondegenerate quantum codes. In this article we show that Calderbank-Shor-Steane (CSS) codes, over a prime power alphabet $q⩾5$, cannot beat the quantum Hamming bound. We prove a quantum version of the Griesmer bound for the CSS codes, which allows us to strengthen the Rains’ bound that an $[[n,k,d]{]}_2$ code cannot correct more than $\lfloor (n+1)/6\rfloor$ errors to $\lfloor (n-k+1)/6\rfloor$. Additionally, we also show that any $[[n,k,d]{]}_q$ quantum code with $k+d⩽(1-2{\mathit{eq}}^{-2})n$ cannot beat the quantum Hamming bound.

The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones polynomial by nuclear magnetic resonance (NMR); in addition, we show how to escape from the limitations of NMR approaches that employ pseudopure states. Specifically, we use two spin-1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the trefoil knot, the figure-eight knot, and the Borromean rings. After measuring the nuclear spin state of the molecule in each case, we are able to estimate the value of the Jones polynomial for each of the knots.

We study the current-phase relation of a Bose-Einstein condensate flowing through a repulsive square barrier by solving analytically the one-dimensional Gross-Pitaevskii equation. The barrier height and width fix the current-phase relation $j(\delta \varphi )$, which tends to $j~\cos (\delta \varphi /2)$ for weak barriers and to the Josephson sinusoidal relation $j~\sin (\delta \varphi )$ for strong barriers. Between these two limits, the current-phase relation depends on the barrier width. In particular, for wide-enough barriers, we observe two families of multivalued current-phase relations. Diagrams belonging to the first family, already known in the literature, can have two different positive values of the current at the same phase difference. The second family, new to our knowledge, can instead allow for three different positive currents still corresponding to the same phase difference. Finally, we show that the multivalued behavior arises from the competition between hydrodynamic and nonlinear-dispersive components of the flow, the latter due to the presence of a soliton inside the barrier region.

We propose a dressed subwavelength metal slit structure, which is formed by adding a thin metallic grating near the slit entrance with a distance. The simulation computation by means of the finite-difference time-domain method shows that the transmissivity can be substantially enhanced by 30 times compared with the conventional metal slit structure. The transmission spectrum exhibits two characters of the Fabry-Perot resonance and a left-shift. The introduced grating has two effects: (1) more energy is collected from the incident plane, and (2) the effective dielectric region in the slit is extended to the region out of the entrance.