The classical trajectory Monte Carlo method is applied to the calculation of single- and double-ionization cross sections of helium atoms by proton and antiproton impacts. The classical helium atom is stabilized by the introduction of the Heisenberg core potentials that prevent autoionization of classical two-electron atoms under the constraint of the uncertainty principle. The ratio of the double- to single-ionization cross sections is larger for antiproton impact than for proton impact in agreement with measurements, though the difference is slightly smaller than the experimental findings. It is important to generate the initial distribution microcanonically taking all the possible configurations into account. Exclusive use of the circular orbits fails to account for the dependence on the projectile charge. The Bohr helium model without the stabilization is too fragile to be used for collision problems of charged particles even at high energies.

We extend the exterior-complex-scaling–generalized-pseudospectral (ECSGPS) method [D. A. Telnov and S. I. Chu, Phys. Rev. A 59, 2864 (1999)] to the nonperturbative calculations of complex-quasienergy resonances of many-electron quantum systems within the Floquet formulation of time-dependent density-functional theory (TDDFT) [D. A. Telnov and S. I. Chu, Chem. Phys. Lett. 264, 466 (1997)]. The ECSGPS technique appears very useful in TDDFT-Floquet calculations where the exchange-correlation potentials may exhibit quite complicated behavior as functions of the electron coordinates and cannot be easily treated by means of the uniform-complex-scaling techniques. We have applied this procedure to the study of one-photon detachment and two-photon dominant above-threshold detachment of ${\mathrm{Li}}^{-}$ negative ions. In the one-photon case, the photodetachment cross section has been calculated as a function of the photon energy with results in good agreement with the experimental data. In the two-photon case, both the partial detachment rates and electron angular distributions for the dominant and above-threshold channels are presented for a range of laser field frequencies and intensities. Dramatic transformations of the angular distributions in the vicinity of the two-photon threshold are observed and analyzed.

The pulsed output from a Bose-Einstein condensate can be described using ordinary one-particle quantum mechanics. The initial state is described in terms of Stark resonances truncated in momentum space. The states obtained in this way resemble the normalizable scattering states defined in terms of Moshinsky functions. The validity of this approach and the influence of the initial population on the pulse formation is discussed. Finally, we describe an experimental setup to manufacture and observe pulsed output in Wannier-Stark systems.

We generalize the quantum optical input-output theory developed for optical cavities to ultracold fermionic atoms confined in a trapping potential, which forms an “atom cavity.” In order to account for the Pauli exclusion principle, quantum Langevin equations for all cavity modes are derived. The dissipative part of these multimode Langevin equations includes a coupling between cavity modes. We also derive a set of boundary conditions for the Fermi field that relate the output fields to the input fields and the field radiated by the cavity. Starting from a constant uniform current of fermions incident on one side of the cavity, we use the boundary conditions to calculate the occupation numbers and current density for the fermions that are reflected and transmitted by the cavity.

Atom interferometers can be used to study phenomena leading to irreversibility and dissipation, induced by the dynamics of fundamental objects (strings and branes) at a large mass scale. Using an effective, but physically consistent description in terms of a master equation of Lindblad form, the modifications of the interferometric pattern induced by the new phenomena are analyzed in detail. We find that present experimental devices can, in principle, provide stringent bounds on the new effects.

We derive a non-Markovian generalization to the quantum kinetic theory described by Walser et al. [Phys. Rev. A 59, 3878 (1999)] in the absence of a condensed fraction for temperatures above the Bose-Einstein condensation temperature i.e., $T>\mathrm{}{T}_c.$ Within this framework, quasiparticle damping arises naturally due the finite duration of a binary collision and it leads to a systematic Markov approximation from the non-Markovian Born theory. Such a self-consistent theory conserves the total energy to second order in the interaction strength. By introducing an improved damping function, we demonstrate global energy conservation at the order of the perturbation theory. Finally, we apply this kinetic theory to a simple model of an inhomogeneous Bose gas that is confined in a spherical box. By studying numerically the real-time quantum evolution towards equilibrium, we obtain damping rates and frequencies of the collective modes and illustrate the emergence of differing time scales for correlation and relaxation.

A Raman configuration consisting of two pairs of counterpropagating traveling wave fields is shown to lead to optical potentials having $\lambda /8\mathrm{}$ periodicity. Such optical potentials may be used to construct optical lattices having $\lambda /8\mathrm{}$ periodicity. Using numerical diagonalization, we obtain the optical potentials for ${}^{85}\mathrm{Rb}$ atoms.

A very recent proposal for performing quantum search without entanglement by optical means is briefly discussed. Since the search of a simple, completely unstructured list or its equivalent is involved, it appears that exponential resources are required. Therefore the proposed search of a Rydberg-atom array is not practicable for quantum computing.

We consider an analog of the internal Josephson effect in superfluid atomic Fermi gases. Four different hyperfine states of the atoms are assumed to be trapped and to form two superfluids via the BCS type of pairing. We show that Josephson oscillations can be realized by coupling the superfluids with two laser fields. Choosing the laser detunings in a suitable way leads to an asymmetric below-gap tunneling effect for which there exists no analog in the context of solid-state superconductivity.

We have investigated Bose-Einstein condensates and ultracold atoms in the vicinity of a surface of a magnetic microtrap. The atoms are prepared along copper conductors at distances to the surface between $300\mu \mathrm{m}$ and $20\mu \mathrm{m}.$ In this range, the lifetime decreases from 20 s to 0.7 s showing a linear dependence on the distance to the surface. The atoms manifest a weak thermal coupling to the surface, with measured heating rates remaining below 500 nK/s. In addition, we observe a periodic fragmentation of the condensate and thermal clouds when the surface is approached.

Given a spatially dependent mass distribution, we obtain potential functions for exactly solvable nonrelativistic problems. The energy spectrum of the bound states and their wave functions are written down explicitly. This is accomplished by mapping the wave equation for these systems into well-known exactly solvable Schrödinger equations with constant mass using point canonical transformation. The Oscillator, Coulomb, and Morse class of potentials are considered.

We investigate the conditions under which unconditional dense coding can be achieved using continuous-variable entanglement. We consider the effect of entanglement impurity and detector efficiency and discuss experimental verification. We conclude that the requirements for a strong demonstration are not as stringent as previously thought, and are within the reach of present technology.

A comprehensive study is presented of the scattering of protons on ${\mathrm{H}}_2\left({\nu }_i\right)$ and of hydrogen atoms on ${\mathrm{H}}_2^{+}\left({\nu }_i\right),$ where ${\nu }_i$ is any vibrationally excited state of the relevant molecules. Cross sections for charge transfer and excitation have been calculated in the range of center-of-mass energies 0.6–9.5 eV using a fully quantal, coupled-channel approach. An extensive vibrational basis set, defined in a large configuration space of the reactants, is used, including a large number of discretized vibrational continua. A detailed picture is produced of all inelastic processes that involve two lowest, nonadiabatically coupled electronic surfaces of the ${\mathrm{H}}_3^{+}$ molecule. The rotational dynamics of ${\mathrm{H}}_2$ and ${\mathrm{H}}_2^{+}$ are treated within the sudden approximation. The cross sections obtained are compared with the sparse data available from literature.

We show that Rabi resonances can be used to assess field strength in terms of time at the atomic level. Rabi resonances are enhancements in the amplitude of atomic population oscillations when the Rabi frequency, Ω, “matches” a field-modulation frequency, ${\omega }_m.$ We demonstrate that $\Omega =2\mathrm{}\kappa {\omega }_m$ and find that $\kappa =1.03\mathrm{}\pm \mathrm{0.05.}$ Since Ω is defined by field strength (i.e., photon number) through atomic constants, and ${\omega }_m$ may be referenced to an atomic clock, our work shows that Rabi resonances provide a connection between time and photon number.

We analyze depletion of the dark soliton in a Bose-Einstein condensate in the limit of weak interaction between atoms. The condensate initially prepared in the excited dark soliton state is losing atoms because of spontaneous quantum depletion. These atoms are depleted from the soliton state into single-particle states with nonzero density in the notch of the soliton. As a result the image of the soliton is losing contrast. This quantum depletion mechanism is efficient even at zero temperature when a thermal cloud is absent.

In this paper we present a state vector analysis of the generation of atomic spin squeezing by the measurement of an optical phase shift. The frequency resolution is improved when a spin squeezed sample is used for spectroscopy in place of an uncorrelated sample. When light is transmitted through an atomic sample some photons will be scattered out of the incident beam, and this has a destructive effect on the squeezing. We present quantitative studies for three limiting cases: the case of a sample of atoms of size smaller than the optical wavelength, the case of a large dilute sample, and the case of a large dense sample.

We examine the competition among one- and two-photon processes in an ultracold, three-level atom undergoing cascade transitions as a result of its interaction with a bimodal cavity. We show parameter domains where two-photon transitions are dominant, and we also study the effect of two-photon emission on the mazer action in the cavity. The two-photon emission leads to the loss of detailed balance and therefore we obtain the photon statistics of the cavity field by the numerical integration of the master equation. The photon distribution in each cavity mode exhibits sub- and super-Poissonian behaviors depending on the strength of atom-field coupling. The photon distribution becomes identical to a Poisson distribution when the atom-field coupling strengths of the modes are equal.

We define a “nit” as a radix n measure of quantum information which is based on state partitions associated with the outcomes of n-ary observables and which, for $n>\mathrm{}2,$ is fundamentally irreducible to a binary coding. Properties of this measure for entangled many-particle states are discussed. k particles specify k nits in such a way that k mutually commuting measurements of observables with n possible outcomes are sufficient to determine the information.

In a recent paper, Bo Liu and Xi-Jing Ning [Phys. Rev. A 64, 013401 (2001)] compared a multistep photoionization scheme where the resonant laser pulses act in consecutive order with one where the same laser pulses act simultaneously. Their conclusion is that the “consecutive” scheme is much more (several orders of magnitude) efficient than the “simultaneous” one, which they call traditional. We show, however, that optimum conditions for efficient photoionization with the simultaneous (or traditional) scheme are very different from those assumed by the authors. So the difference between two schemes, in terms of efficiency, is of much lower importance, if any, than that believed by the authors.