We report Monte Carlo wave-function simulation results for two colliding atoms in a blue-detuned near-resonant $J=\overrightarrow{1}J=1\mathrm{}$ optical lattice. Our results show that complete optical shielding of collisions can be achieved within the lattice with suitably selected and realistic laser field parameters. More importantly, our results demonstrate that the shielding effect does not interfere with the actual trapping and cooling process, and it is produced by the lattice lasers themselves, without the need to use additional laser beams.

We propose a scheme for entangling the motional mode of a trapped atom with a propagating light field via a cavity-mediated parametric interaction. We then show that if this light field is subsequently coupled to a second distant atom via a cavity-mediated linear-mixing interaction, it is possible to transfer the entanglement from the light beam to the motional mode of the second atom to create an Einstein-Podolsky-Rosen–type entangled state of the positions and momenta of two distantly separated atoms.

We describe the operation and tolerances of a nondeterministic, coincidence basis, quantum controlled-NOT gate for photonic qubits. It is constructed solely from linear optical elements and requires only a two-photon source for its demonstration. Its success probability is $1/9.$

We evaluate the $\mathcal{l}$-wave Jost function for the polarization potential and calculate its effective range expansion for $\mathcal{l}=0\mathrm{}$ up to the order $k^4.$ We investigate not only the phase but also the modulus of the Jost function, generalizing previous works for the expansion up to the order $k^2$ of the s-wave phase shift. We discuss the validity domain of this generalized expansion for the interaction of an electron with a Helium atom in any of its three long-lived He states, i.e., $1^{1}S,$ $2^{1}S,$ and $2^{3}S.\mathrm{}$ Even though this expansion is shown to be appropriate for most of the applications in electron-atom collisions, we propose here a more precise and simpler approach that provides much better results in a broader energy range when comparing with elaborated ab initio calculations.

Two-photon above-threshold ionization cross sections and angular distributions have been calculated for Mg in the region between the $3p$ and $4s$ ionization thresholds. We have used the Green’s function method in the Feshbach formalism and an $L^2$ close coupling method, with a basis of $L^2$ integrable B-spline functions. We report the positions, widths, and assignments of a number of ${}^1{S}^e$ and ${}^1{D}^e$ doubly excited Feshbach states. We have found that correlation is important in the Feshbach states, indicated by significant mixing among configurations, and identified a previously unnoticed $“3d5g”$ Feshbach state.

We consider a system consisting of an atom in the approximation of a harmonic oscillator of frequency $\overline{\omega },$ coupled to the scalar potential inside a spherical reflecting cavity of radius R. We use dressed states introduced in a previous publication [Andion, Malbouisson, and Mattos Neto, J. Phys. A 34, 3735 (2001)], which allow a nonperturbative unified description of the atom radiation process, in both cases, of a finite or an arbitrarily large cavity. We perform a study of the energy distribution in a small cavity, with the initial condition that the atom is in the first excited state and we conclude for the quasi-stability of the excited atom. For instance, for a frequency $\overline{\omega }$ of the order $\overline{\omega }\sim 4.00\times {10}^{14}/\mathrm{s}$ (in the visible red), starting from the initial condition that the atom is in the first excited level, we find that for a cavity with diameter $2R\sim 1.0\times {10}^{-6}\hspace{0.5em}\mathrm{m},$ the probability of the atom being at any time still in the first excited level, will be of the order of 97%. For a typical microwave frequency $\overline{\omega }\sim 2.00\times {10}^{10}/\mathrm{s}$ we find stability in the first excited state also of the order of 97% for a cavity radius $R\sim 1.4\times {10}^{-2}\hspace{0.5em}\mathrm{m}.$

We consider a system of two interpenetrating Bose-Einstein condensates of atoms in two different hyperfine spin states. We show that in the presence of a small coupling drive between the two spin levels, there exist domain walls across which the relative phase of the two condensates changes by $2\pi .$ We give the physical interpretation of such walls. We show that the wall tension determines the force between certain pairs of vortices at large distances. We also show that the probability of the spontaneous decay of the domain wall is exponentially suppressed, both at finite and at zero temperature, and determine the exponents in the regime of small Rabi frequency. We briefly discuss how such domain walls could be created in future experiments.

We propose a numerical algorithm for finding optimal measurements for quantum-state discrimination. The theory of the semidefinite programming provides a simple check of the optimality of the numerically obtained results. With the help of our algorithm we calculate the minimum attainable error rate of a device discriminating between three particularly chosen pure qubit states.

We develop a theory of equilibrium properties and dissipative dynamics of large vortex arrays in trapped Bose-condensed gases. We prove that, in spite of the spatial inhomogeneity of the condensate density profile in trapped gases, the equilibrium configuration corresponds to a vortex array of uniform density. We show that in a static trap the interaction of the vortex array with thermal excitations leads to a nonexponential decay of the vortex structure, and the characteristic lifetime depends on the initial density of vortices. Drawing an analogy with physics of pulsars, we propose an experiment that employs the decay induced heating of the thermal cloud as a tool for a nondestructive study of the vortex dynamics.

The differences between quantum and classical dynamics can be studied through the moments and correlations of the position and momentum variables in corresponding quantum and classical statistical states. In chaotic states the quantum-classical differences grow exponentially with an exponent that exceeds the classical Lyapunov exponent. It is shown analytically that the quantum-classical differences scale as ${ħ}^2,$ and that the exponent for the growth of these differences is independent of ħ. The quantum-classical difference exponent is studied for two quartic potential models, and the results are compared with previous work on the Hénon-Heiles model.

Equivalent-neighbor interactions of the conduction-band electron spins of quantum dots in the model of Imamoḡlu et al. [Phys. Rev. Lett. 83, 4204 (1999)] are analyzed. An analytical solution and its Schmidt decomposition are found and applied to evaluate how much the initially excited dots can be entangled with the remaining dots if all of them are initially disentangled. It is demonstrated that perfect maximally entangled states (MES’s) can only be generated in systems of up to six dots with a single dot initially excited. It is also shown that highly entangled states, approximating the MES’s with good accuracy, can still be generated in systems of odd numbers of dots with almost half of them excited. A sudden decrease of entanglement is observed on increasing the total number of dots in a system with a fixed number of excitations.

We introduce a notion of set discrimination, which is an interesting extension of quantum state discrimination. A state is secretly chosen from a number of quantum states, which are partitioned into some disjoint sets. A set discrimination is required to identify which set the given state belongs to. Several essential problems are addressed in this paper, including the condition of perfect set discrimination, unambiguous set discrimination, and in the latter case, the efficiency of the discrimination. This generalizes some important results on quantum state discrimination in the literature. A combination of state and set discrimination and the efficiency are also studied.

Thermodesorption of impurities from a dielectric crystal surface can be stimulated by absorption of high-frequency phonons, e.g., Debye phonons. We study this process in the framework of a truncated-harmonic-oscillator model and find the desorption rate by methods of quantum statistics. In this paper, we present the estimates for the mean desorption rates that are simple, realistic, and at the same time allow us to predict a series of physical effects in thermodesorption processes.

We investigate theoretically the Raman coupling between two internal states of a trapped low-density quantum-degenerate Fermi gas. In general, the trap frequencies associated with the two internal states can be different, leading to the onset of collapses and revivals in the population difference $\Delta N$ of the two internal states. This behavior can be changed drastically by two-body collisions. In particular, we show that under appropriate conditions they can suppress the dephasing leading to the collapse of $\Delta N,$ and restore almost full Rabi oscillations between the two internal states. These results are compared and contrasted to those for a quantum-degenerate bosonic gas.

We develop a dynamical model suitable for the description of two mutually coupled semiconductor lasers in a face-to-face configuration. Our study considers the propagation of the electric field along the compound system as well as the evolution of the carrier densities within each semiconductor laser. Mutual injection, passive optical feedback, and multiple reflections are accounted for in this framework, although under weak to moderate coupling conditions. We systematically describe the effect of the coupling strength on the spectrum of monochromatic solutions and on the respective dynamical behavior. By assuming single-longitudinal-mode operation, weak mutual coupling and slowly varying approximation, the dynamical model can be reduced to rate equations describing the mutual injection from one laser to its counterpart and vice versa. A good agreement between the complete and simplified models is found for small coupling. For larger coupling, higher-order terms lead to a smaller threshold reduction, reflected itself in the spectrum of the monochromatic solutions and in the dynamics of the optical power.

The Casimir force acting between two test bodies made of different metals is considered. The finiteness of the conductivity of the metals is taken into account perturbatively up to the fourth order of the relative penetration depths of electromagnetic zero-point oscillations into the metals. The influence of nonzero temperature is computed explicitly for separate orders of perturbation and found to be important in the zeroth and first orders only. The configurations of two parallel plates and a sphere (spherical lens) above a plate are considered made of Au and Cr. The obtained results can be used also to take into account the surface roughness. Thus, the total amount of the Casimir force between different metals with all correction factors is determined. This may be useful in various applications.

We advance a self-consistent multiplicative constant (SCMC) method based on a local exchange potential that yields total, exchange, and atomization energies approaching quite closely, but at a much lower computational cost, those of the exact orbital-dependent exchange treatment [S. Ivanov, S. Hirata, and R. J. Bartlett, Phys. Rev. Lett. 83, 5455 (1999); A. Görling, ibid. 83, 5459 (1999)]. Application of the SCMC method to any approximate exchange energy functional permits us to remove the self-interaction correction from the latter as well as to restore its variational character. The SCMC method is implemented here using the following exchange energy functionals: local-density approximation, the Perdew-Wang 1991, Becke 1988, and the one-parameter hybrid Becke Lee-Yang-Parr functional. Calculations for atoms and diatomic molecules are presented. In addition, we prove that the exchange energy evaluated from the Kohn-Sham exchange-only determinant is an upper bound to the Hartree-Fock exchange energy.

Atomic and molecular ground-state energies are variationally determined by constraining the two-particle reduced density matrix (2-RDM) to satisfy positivity conditions. Because each positivity condition corresponds to correcting the ground-state energies for a class of Hamiltonians with two-particle interactions, these conditions collectively provide a new approach to many-body theory that, unlike perturbation theory, can capture significantly correlated phenomena including the multireference effects of potential-energy surfaces. The D, Q, and G conditions for the 2-RDM are extended through generalized lifting operators inspired from the formal solution of N-representability. These lifted conditions agree with the hierarchy of positivity conditions presented by Mazziotti and Erdahl [Phys. Rev. A 63, 042113 (2001)]. The connection between positivity and the formal solution explains how constraining higher RDMs to be positive semidefinite improves the N representability of the 2-RDM and suggests using pieces of higher positivity conditions that computationally scale like the D condition. With the D, Q, and G conditions as well as pieces of higher positivity the electronic energies for Be, LiH, ${\mathrm{H}}_2\mathrm{O},$ and BH are computed through a primal-dual interior-point algorithm for positive semidefinite programming. The variational method produces potential-energy surfaces that are highly accurate even far from the equilibrium geometry where single-reference perturbation-based methods often fail to produce realistic energies.

The Ca $2p$ resonances at 345–355 eV were studied by photoion and photoelectron spectroscopy using monochromatized synchrotron radiation and atomic-beam technique. The analysis of the excitation and decay of these resonances shows strong configuration mixing between the different subshells of the valence electrons $4s,$ $3d,$ and $4p.$ In the case of the ${2p}_{3/2}^{-1}$ resonance structure at 348 eV there are two excited states with nearly equal contributions from the configuration ${2p}^5{3d4s}^2$ and ${2p}^5{3d}^{2}4s,$ which gives rise to strong variations of the resonantly enhanced ${3p}^4{\mathrm{}(3d,4s)\mathrm{}}^3$ photoelectron lines when scanning the photon energy across the resonance.