Absolute differential cross sections (DCSs) are reported for charge-transfer scattering of (1–5)-keV ${\mathrm{O}}^{+}{(}^{4}S)$ ground-state and ${\mathrm{O}}^{+}{(}^2{D,}^{2}P)$ metastable-state ions by helium atoms at angles between $0.2°$ and $6.3°$ in the laboratory frame. Estimated ground-state and metastable-state total cross sections are derived from these measurements. The present ground-state cross sections agree satisfactorily with previous measurements for energies above 2 keV and the metastable-state cross sections are consistent with the mixed-state data of Kusakabe et al. [J. Phys. Soc. Japan 59, 1987 (1990)]. The large differences between the ground- and metastable-state cross sections predicted by theory are not observed.

We derive some general characteristics of the wave function representing a break-up event, in the asymptotic region. They have a strong bearing on the validity of some classical pictures, on the correlation between spatial and momentum variables that develops in the course of the dissociation process and on stringent requirements on the basis sets that are employed to approximate the wave function. Although other calculations are mentioned to underline the generality of our reasonings, we restrict most of the presentation, and all of the illustrations, to the case of ionization.

Coulomb interaction is characterized by two nondimensional fundamental quantities: the Sommerfeld parameter $\eta$ and the adiabaticity parameter $\xi ={\eta }_f-{\eta }_i.$ In this different approach, we choose these variables to describe the behavior of the generalized oscillator strength (GOS). The expression we obtain is valid for scattering of electrons, positrons, and nuclei by arbitrary targets. We present asymptotic expansions, in the quantal and semiclassical approximation, of the electric dipole GOS.

We report the first detailed decay studies of trapped metastable $\mathrm{}\left(2S\right)\mathrm{}$ hydrogen. By two-photon excitation of ultracold H samples, we have produced clouds of at least $5\times {10}^7$ magnetically trapped $2S$ atoms at densities greater than $4\times {10}^{10}{\mathrm{cm}}^{-3}$ and temperatures below $100\mu \mathrm{K}.$ At these densities and temperatures, two-body inelastic collisions of metastable atoms are evident. Experimental values for the total two-body loss rate constant are $K_2{=1.8\mathrm{}}_{-0.7}^{+1.8\mathrm{}}\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $87\mu \mathrm{K}$ and $K_2{=1.0\mathrm{}}_{-0.5}^{+0.9\mathrm{}}\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $230\mu \mathrm{K}.$ These results are in the range of recent theoretical calculations for the total $2S-2S$ inelastic rate constant. The metastable clouds were excited in a gas of ground-state $\mathrm{}\left(1S\right)\mathrm{}$ hydrogen with peak densities reaching $7\times {10}^{13}{\mathrm{cm}}^{-3}.$ From the one-body component of the metastable decay, we derive experimental upper limits for $K_{12},$ the rate constant for loss due to inelastic $1S-2S$ collisions.

Results of calculations of the near-threshold photoionization of the xenon $3d$ spin-orbit doublet are reported. Our theoretical analysis is undertaken in order to interpret and enlighten the very detailed measurements of this process [A. Kivimäki et al., Phys. Rev. A 63, 012716 (2001)], which revealed a previously unobserved interesting feature—an additional broad maximum—in the partial xenon ${3d}_{5/2}$ cross section. This double maximum was not produced by earlier calculations, except in the recent study by Amusia et al. [Phys. Rev. Lett. 88, 093002 (2002)], which, in contrast to the present one, is not ab initio and relativistic in character. The partial photoionization cross sections of ${3d}_{5/2}$ and ${3d}_{3/2}$ subshells, photoelectron anisotropy parameters, and spin-polarization parameters that were so far not studied either experimentally or theoretically are calculated. Many-electron correlations, relativistic effects, and relaxation effects of the ionic core in the ionization process are taken into account by using the relativistic random-phase approximation, modified to include the relaxation of the considered subshell.

We report calculations of the magnetic decoupling of the nuclear spin relaxation rate of ${}^{129}\mathrm{Xe}$ atoms caused by binary collisions with Rb or Cs atoms in a gas. A semiclassical approximation, using a classical path for the collision and treating the spin interactions quantum mechanically, gives results that differ by no more than 2% from calculations with the distorted-wave Born approximation. Both computational methods show that the relaxation rate decreases substantially for magnetic fields of a few tens of teslas. For ${}^{129}\mathrm{Xe}-\mathrm{Rb},$ where recent experimental measurements are available, the calculated rate coefficients at the experimental field of 9.4 T are about 80% of the calculated values at zero field. At 9.4 T, the calculated rate coefficient for ${}^{129}\mathrm{Xe}-\mathrm{Rb}$ is about one-half of the experimentally observed value. This discrepancy is probably due to inaccuracies in the van der Waals and spin-dependent potentials used in the calculations.

An accidental degeneracy of unbound states gives rise to a double pole in the scattering matrix, a double zero in the Jost function, and a Jordan chain of length 2 of generalized Gamow-Jordan eigenfunctions of the radial Schrödinger equation. The generalized Gamow-Jordan eigenfunctions are basis elements of an expansion in bound- and resonant-state energy eigenfunctions plus a continuum of scattering wave functions of a complex wave number. In this biorthonormal basis, any operator ${f(H}_r^{\left(\mathcal{l}\right)})$ which is a regular function of the Hamiltonian is represented by a complex matrix that is diagonal except for a Jordan block of rank 2. The occurrence of a double pole in the Green’s function, as well as the non exponential time evolution of the Gamow-Jordan generalized eigenfunctions are associated with the Jordan block in the complex energy representation.

We present a theoretical framework for the evolution of the internal state of a fast highly charged one-electron ion traversing an amorphous solid. We employ an open quantum system approach which incorporates the complex array of collisions with electrons and ionic cores in the solid within the framework of system-reservoir interactions. Interactions with the solid environment and the radiation field are treated on the same footing and the quantum master equation for the reduced density matrix of the electronic state of the ion is approximated by a Lindblad equation. The latter allows the solution of this multistate problem in terms of Monte Carlo sampling of quantum trajectories. Similarities and extensions to methods used in quantum optics and previously employed in ion-solid interactions are discussed. Our focus is on the transient buildup and destruction of coherences by stochastic processes. We apply our method to the study of coherence properties of the internal state of a fast ${\mathrm{Kr}}^{35+}$ ion traversing carbon foils. Simulations exhibit clear signatures of partially coherent transitions and are found to be in good agreement with experimental data.

We use a self-consistent, variational-statistical approach to analyze the vicinage effect on charge states of constituent ions in fast large clusters, passing through thin foils. The solutions of the resulting nonlinear integral equation show that the individual ion charges are reduced in comparison to isolated isotachic ions and are distributed nonhomogeneously throughout the cluster. Using a statistical description of the ion positions in conjunction with the nonhomogeneous distribution of ion charges, we evaluate the total stopping power of the cluster by means of the dielectric formalism. It is shown that interference in cluster stopping coming from the spatial correlations among the constituent ions is strongly influenced by the vicinage effect on ion charge states.

We investigate cooling and trapping of single atoms inside an optical cavity using a quasiresonant field and a far-off-resonant mode of the Laguerre-Gauss type. The far-off-resonant doughnut mode provides an efficient trapping in the case when it shifts the atomic internal ground and excited state in the same way, which is particularly useful for quantum information applications of cavity quantum electrodynamics systems. Long trapping times can be achieved, as shown by full three-dimensional simulations of the quasiclassical motion inside the resonator.

We study the existence and the spectral and collisional properties of bright and dark solitons in a Bose-Einstein condensate (BEC) in optical lattices. Both types of these solitons are located on the background of a matter wave of finite amplitude with characteristic frequency lying outside the forbidden gap. Thus we term our solitons out-of-gap solitons. We discuss feasibility of practical preparation of the background wave to observe these solitons and make connections with recent experiments studying BEC in optical lattices. We prove that the dark out-of-gap solitons are robust against perturbations and numerically verify the possibility of their excitation using a phase imprinting technique.

A Bose-Einstein condensate is created in a simple and robust miniature Ioffe-Pritchard trap, the so-called Z trap. This trap results from the mere combination of a Z-shaped current-carrying wire and a homogeneous bias field. The experimental procedure allows condensation of typically $3\times {10}^5$ ${}^{87}\mathrm{Rb}$ atoms in the $|F=2,$ $m_F=2\mathrm{}〉$ state close to any mirroring surface, irrespective of the surface structure. Thus it is ideally suited as a simple coherent source for miniature surface traps or for cold atom physics near surfaces.

Within a scaling ansatz formalism plus Thomas-Fermi approximation, we investigate the collective excitations of a harmonically trapped boson-fermion mixture in the collisionless and hydrodynamic limit at low temperature. Both the monopole and quadrupole modes are considered in the presence of spherical as well as cylindrically symmetric traps. In the spherical traps, the frequency of the monopole mode coincides in the collisionless and hydrodynamic regime, suggesting that it might be undamped in all collisional regimes. In contrast, for the quadrupole mode, the frequency differs largely in these two limits. In particular, we find that in the hydrodynamic regime the quadrupole oscillations with equal bosonic and fermionic amplitudes generate an exact eigenstate of the system, regardless of the boson-fermion interaction. This resembles the Kohn mode for the dipole excitation. We discuss in some detail the behavior of monopole and quadrupole modes as a function of boson-fermion coupling at different boson-boson interaction strength. Analytic solutions valid at weak and medium fermion-boson coupling are also derived and discussed.

We present a one-dimensional (1D) effective model for the evolution of a cigar-shaped Bose-Einstein condensate in time-dependent potentials whose radial component is harmonic. We apply this model to investigate the dynamics and expansion of condensates in 1D optical lattices, by comparing our predictions with recent experimental data and theoretical results. We also discuss negative-mass effects which could be probed during the expansion of a condensate moving in an optical lattice.

We present a calculation of solitary waves propagating in a steady state with constant velocity $v$ along a cigar-shaped Bose-Einstein trap approximated as an infinitely elongated cylinder. For sufficiently weak couplings (densities), the main features of the calculated solitons could be captured by effective one-dimensional (1D) models. However, for stronger couplings of practical interest, the relevant solitary waves are found to be hybrids of quasi-1D solitons and 3D vortex rings. An interesting hierarchy of vortex rings occurs as the effective coupling constant is increased through a sequence of critical values. The energy-momentum dispersion of the above structures is shown to exhibit characteristics similar to a mode proposed sometime ago by Lieb within a strictly 1D model, as well as some rotonlike features.

We consider a Bose-Einstein bicondensate of ${}^{87}\mathrm{Rb},$ trapped in two different internal levels, in a situation where the density undergoes a symmetry breaking in momentum space. This occurs for a suitable number of condensed atoms within a double-well dispersion curve, obtained by Raman coupling two internal states with two tilted and detuned light fields. Evidence of bistability results from the Gross-Pitaevskii equation. By second quantization, we evaluate the tunneling rate between the two asymmetric states; the effects of losses on coherence are negligible.

We present a comprehensive framework for treating the nonlinear interaction of few-cycle pulses using an envelope description that goes beyond the traditional slowly varying envelope approximation method. This is applied to a range of simulations that demonstrate how the effect of a ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$ nonlinearity differs between the many-cycle and few-cycle cases. Our approach, which includes diffraction, dispersion, multiple fields, and a wide range of nonlinearities, builds upon the work of Brabec and Krausz [T. Brabec and F. Krausz, Phys. Rev. Lett. 78, 3282 (1997)] and Porras [M. A. Porras, Phys. Rev. A 60, 5069 (1999)]. No approximations are made until the final stage when a particular problem is considered.

We show how a medium, under the influence of a coherent control field that is resonant or close to resonance to an appropriate atomic transition, can lead to very strong asymmetries in the propagation of unpolarized light when the direction of the magnetic field is reversed. We show how electromagnetically induced transparency (EIT) can be used in atomic vapor to mimic this magnetochiral effect that occurs in natural systems. EIT can produce much larger asymmetry than the well-known magnetochiral effect as we use the dipole-allowed transitions here. Using density-matrix calculations we present results for the breakdown of the magnetic-field-reversal symmetry for two different atomic configurations.

In this work a formalism of collective atom-field operators is described and applied to study the dynamics of a classically driven two-level atom inside a band-gap material. We show that if a photon-atom bound state can exist when driving is absent, then it is possible to assume mutual independence of collective operators and develop an effective approximation for the case when driving is present.

We develop a model of a liquid crystal Fabry-Pérot microcavity. We study the homeotropic and the hybrid cavity configurations and show that both are multistable. Moreover, in the hybrid case a branch of solutions disconnected from the zero field solution exists.