Total cross sections for single- and multiple-electron capture and ionization events in ${\mathrm{C}}^{4+}+\mathrm{Ne}$ collisions are calculated in the independent particle model using the nonperturbative basis generator method. Dynamical screening effects due to the removal of electrons from the target atom and due to the capture of electrons to the projectile ion are taken into account in a global fashion. Our data for impact energies from 20 to 2000 keV/amu follow the trends of previous calculations for proton and ${\mathrm{He}}^{2+}$ impact, in particular with respect to the energy dependence of the net electron loss from the target. When comparing our results to available experimental total cross sections for ${\mathrm{C}}^{4+}$ and ${\mathrm{F}}^{4+}$ impact, we find that (1) relative populations of recoil ion charge states are generally well reproduced; (2) the absolute normalizations of experimental data appear to be problematic; and (3) charge-state correlated cross sections are in agreement for processes including up to two electrons, but discrepancies persist for higher electron multiplicities. It is argued that new experimental investigations of global and charge-state correlated cross sections would be helpful to further the understanding of ion-atom collision systems with many active electrons in the regime of medium impact energies.

An experimental and theoretical study of the energy loss of hydrogen, helium, and nitrogen ions in alumina and silica is presented. Experimental data show that silica and alumina have a different stopping behavior. By using a model insulator dielectric function to estimate the target valence electron contribution to the stopping power, we explain the energy loss of point charges in the two oxides and extend the model to helium projectiles, where charge state effects have to be considered. At low velocities this theoretical approach shows a noticeable threshold effect related to the band gap not observed in the experiment. The low velocity data for H, He, and N ions are qualitatively explained using an electron gas model with an effective number of electrons (different for the two oxides) and a nonlinear screening description within density-functional theory. A comparison with Firsov and Lindhard-Scharf models is included for N ions as well.

A spectroscopic approach to the scattering dynamics in the gas-surface boundary layer is presented. The technique utilizes excitation of the vapor atoms in two crossed laser fields, one of which is directed normally to the surface while the other one excites an evanescent wave propagating along the surface. We provide a rigorous and quantitative theoretical description of these two-photon evanescent-volume wave spectra and apply it to the model system of sodium atoms colliding with a dielectric prism surface. A comparison with experimental results reveals quantitative agreement between theory and experiment. We demonstrate that one can distinguish by pure optical means between different groups of atoms, namely atoms moving to the surface and apart from it after being specularly or diffusively scattered. We also extract the two-dimensional velocity distributions of both the arriving and departing groups of atoms.

High-order harmonic emission is calculated for a highly charged ion exposed to an ultra-intense laser field with an intensity near saturation. Low-order harmonics having an energy lower than the ionization potential $I_p$ are emitted with extremely high efficiency. In contrast to their usual behavior, the low-order harmonics may exhibit a plateau that is amenable to a classical mechanism or a resonancelike maximum, depending on the shape of the binding potential. Tunneling is not involved.

At sufficiently high laser intensities, the magnetic-field component of the laser field can strongly influence the stabilization of atoms in the high-frequency regime by inducing motion along the laser pulse propagation direction. Using a two-dimensional model atom, we investigate how the duration of the laser pulse affects stabilization in this nondipole regime. Results obtained using a fully spatially dependent vector potential are compared to a long-wavelength approximation. We also discuss nondipole effects when the atom interacts with two counterpropagating pulses.

Neutron resonance spin echo phenomena, produced by resonance coils with adiabatic passage of the neutron spin, are investigated experimentally and theoretically. The adiabatic passage of the neutron spin through a resonance coil requires a specific configuration of the magnetic field. The solution of the Schrödinger equation, obtained for the required configuration, shows the probability of a spin-flip process; it also shows the phase shift, which the neutron experienced, when it flies through it. The precession phase inside the coil consists of three contributions in the rotating frame approach. The first, biggest contribution is the phase of the rotating frame ${\omega }_0\tau .$ The second is the precession phase of the neutron spin in the rotating frame since it follows adiabatically the effective field as seen in this frame. The third, smallest contribution is Berry’s phase since the magnetic field rotates over an angle approaching $\pi$ in this rotating frame. This rotation is followed adiabatically by the neutron spin. Finally, the amplitude of the interference pattern and the phase shift between the neutron-spin states are derived for a system consisting of two such flippers. The theoretical consideration is experimentally confirmed.

We consider a dilute homogenous atomic Bose-Einstein condensate with two nondegenerate internal energy levels that achieve a state of chemical equilibrium in the presence of an external radiation field that couples the two states. The presence of the radiation field can result in new ground states for the condensate as a consequence of the lowering of the condensate energy due to the interaction energy with the field. We analyze the ground-state energy as a function of the coupling constants for the two-body interactions, the Rabi frequency of the radiation field, and the detuning of the field, and we give explicit expressions for the quasiparticle excitation spectrum.

The collisional interaction in a Bose condensate represents a nonlinearity that in analogy with nonlinear optics gives rise to unique quantum features. In this paper, we apply a Monte Carlo method based on the positive-P pseudoprobability distribution from quantum optics to analyze the efficiency of spin squeezing by collisions in a two-component condensate. The squeezing can be controlled by choosing appropiate collision parameters or by manipulating the motional states of the two components.

We present a general method for obtaining all Bell inequalities for a given experimental setup. Although the algorithm runs slowly, we apply it to two cases. First, the Greenberger-Horne-Zeilinger setup with three observers each performing one of two possible measurements. Second, the case of two observers each performing one of three possible experiments. In both cases we obtain hundreds of inequalities. Since this is the set of all inequalities, the one that is maximally violated in a given quantum state must be among them. We demonstrate this fact with a few examples. We also note the deep connection between the inequalities and classical logic, and their violation with quantum logic.

We present a setup for a direct, total teleportation of a single-particle entangled state. Our scheme consists of a parametric downconversion source, which emits a pair of entangled photons, and a dual Bell measurement system with two beam splitters and two pairs of detectors. An entangled state shared by a pair of beams can be directly transferred to another pair of beams with a 50% probability of success. By a straightforward generalization of the scheme, total teleportation of a multiparticle entangled state can also be performed.

In a recent paper, R. K. Nesbet [Phys. Rev. A 58, R12 (1998)] has compared the single-particle kinetic energy from the Kohn-Sham reference state theory with that of the Thomas-Fermi-like form of the density-functional theory. We argue that, contrary to his opinion, both theories should give the same results for N-electron ground-state density. We show also that there is no inconsistency between the kinetic-energy forms of the two theories, and no need to extend the definition of functional derivatives.

A type of solution to the nonlinear Schrödinger equation for periodically driven Bose-Einstein condensates is introduced, which generalizes the familiar single-particle Floquet states. These solutions lead to the prediction that the onset of self-trapping of a condensate in a periodically modulated double well can be systematically controlled. This mean-field prediction is confirmed on the N-particle level, and explained by a pairing mechanism.

The energy levels in D waves for the parahelium and the orthohelium with both odd and even parity are calculated directly from the Schrödinger equation. After removing the translational and rotational degrees of freedom, only three internal variables are involved in both the functions and the equations. The appropriate internal variables are chosen to remove the singularity in the solutions and to improve the convergence of the series in calculation.

Very simple duality relations assessing complementarity for two-dimensional systems are obtained by introducing a measure of fluctuations derived from dispersion. These relations fully explain the enforcement of complementarity in situations in which the standard position-momentum uncertainty relation plays no role.

For a time-dependent classical quadratic oscillator we introduce pairs of real and complex invariants that are linear in position and momentum. Each pair of invariants realize explicitly a canonical transformation from the phase space to the invariant space, in which the action-phase variables are defined. We find the action operator for the time-dependent quantum oscillator via the classical-quantum correspondence. Candidate phase operators conjugate to the action operator are discussed, but no satisfactory ones are found.

In this article, protocols for quantum key distribution based on encoding in higher dimensional systems in N-dimensional Hilbert space are proposed. We extend the original Bennett-Brassard protocol using two complementary bases and two-dimensional states to M mutually complementary bases and N orthogonal vectors in each base. We study the mutual information between the legitimate parties and the eavesdropper and the error rate by considering various incoherent eavesdropping attacks as a function of the dimension of the Hilbert space.

A method for creating pseudopure states in NMR is described that combines spatial averaging and logical labeling techniques. This method uses one labeling qubit and any desired pseudopure state of any number of qubits can be created in the subsystem manifolds of the labeling qubit. The method uses a nonselective $\pi /2\mathrm{}$ radio frequency pulse on all the nonlabeling qubits to equalize the populations of all the states within each subsystem, followed by a single transition-selective $\pi$ pulse on one of the transitions of the labeling qubit. The transverse magnetization created during the process is destroyed by a magnetic field gradient pulse, yielding a subsystem pseudopure state. The method is demonstrated experimentally on a system of three qubits.

The electrostatic heavy-ion storage ring, ELISA is utilized to measure the lifetime of the metastable $1s2s2p{}^4{P}_{5/2}$ level of the ${\mathrm{He}}^{-}$ ion together with the average lifetime of the ${}^4{P}_{1/2}$ and ${}^4{P}_{3/2}$ levels. This storage ring allows lifetime measurements to be performed without the influence of magnetic fields, and at temperatures below $-50°\mathrm{C},$ which reduces the photodetachment of ${\mathrm{He}}^{-}$ due to blackbody radiation. The lifetime of the ${}^4{P}_{5/2}$ level is determined to be $365\pm 3\hspace{0.5em}\mu \mathrm{s},$ in agreement with, but more accurate than, a previous magnetic storage ring measurement, and 6% longer than the lifetime recently reported utilizing an electrostatic ion trap [Wolf et al., Phys. Rev. A 59, 267 (1999)]. The average lifetime of the ${}^4{P}_{1/2}$ and ${}^4{P}_{3/2}$ levels is determined to be $11.1\pm 0.3\hspace{0.5em}\mu \mathrm{s},$ in agreement with theoretical predictions, but about 25% longer than the reported value from the electrostatic ion trap experiment.

The total cross sections for single-electron capture and transfer ionization are computed for ${\mathrm{Li}}^{3+}+\mathrm{H}\mathrm{e}$ collisions in a four-body distorted-wave formalism. The contribution from the $e-e$ interaction during the collision is evaluated. Comparison between the present theoretical results and measurements at 50–5000 keV/amu yields satisfactory agreement. The continuum distorted-wave four-body method employed can provide information about the relative significance of the dynamic interelectron interaction in the collisions under study.