The linear and circular polarization of photons emitted in radiative electron capture (or, equivalently, radiative recombination in the electron’s rest frame) by bare relativistic high-$Z$ projectiles is calculated. In this paper we illustrate for specific examples and a limited systematics the range of phenomena and the physical insight that can be gained by measuring the polarization of photons emitted in radiative electron capture into bare ions. In particular, we investigate the dependence of the polarization in the reaction plane on the charge and the energy of the projectile. In specific examples, we also consider the contribution of spin-flip processes and the polarization off the reaction plane.

The statistical distributions of the number of simultaneously emitted secondary electrons (SE’s) from a thin carbon foil induced by the frozen-charged ${\mathrm{H}}^0$ and ${\mathrm{H}}^{+}$ projectiles of 2.5–3.5 MeV have been measured by using the coincidence technique with the foil-transmitted particles. The measurement was carried out at the forward and backward directions of the incident beam separately. For frozen-charged ${\mathrm{H}}^0,$ the average SE yields per projectile at the forward direction, ${\gamma }_{\mathrm{F}},$ and at the backward direction, ${\gamma }_{\mathrm{B}},$ are significantly smaller than the corresponding ones for ${\mathrm{H}}^{+}$ due to the screening effect of its bound electron. In addition to the suppression of low-energy electron production for ${\mathrm{H}}^0,$ the preferential forward emission of high-energy electrons makes the proton-hydrogen difference in the ratio of ${\gamma }_{\mathrm{B}}$ to the stopping power more striking. Although the probability of simultaneous n electron emission per unit projectile, $W_n,$ for ${\mathrm{H}}^0$ is significantly smaller than that for ${\mathrm{H}}^{+}$ at small n, their difference decreases with increasing n both at the forward and backward directions. This behavior of $W_n$ also suggests that there is not a large proton-hydrogen difference in the production of high-energy electrons. As a result of a simple model calculation, the difference between the emission statistics by ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ can be well reproduced by a Poisson distribution with a mean equal to the difference of their ${\gamma }_{\mathrm{F}}$ or ${\gamma }_{\mathrm{B}}$ values and the validity of the above-mentioned interpretation on the proton-hydrogen difference of the SE emission is quantitatively confirmed.

We have investigated equilibrium geometries of mixed clusters ${\mathrm{Na}}_{8-x}{\mathrm{Li}}_x$ $(x=0\mathrm{}–8)$ using ab initio molecular dynamics within the framework of density functional theory. The resulting cluster geometries show evolution from $C_{3v}$ symmetry for ${\mathrm{Li}}_8$ to $D_{2d}$ symmetry for ${\mathrm{Na}}_8$ via $T_d$ symmetry $\left({\mathrm{Li}}_4{\mathrm{Na}}_4\right).\mathrm{}$ We also present and discuss the absorption spectra obtained using the time-dependent local density approximation formalism. The calculated absorption spectra of all ${\mathrm{Na}}_{8-x}{\mathrm{Li}}_x$ clusters demonstrate the presence of a strong plasmon peak located approximately at the same energy $\left(\approx 2.7\hspace{0.5em}\mathrm{eV}\right).\mathrm{}$ Our calculations predict nearly the same oscillator strengths for the main plasmon peaks of ${\mathrm{Li}}_8$ and ${\mathrm{Na}}_8.$ Since the polarizabilities of ${\mathrm{Li}}_8$ $\left(9.7\mathrm{}\hspace{0.5em}{\mathrm{\AA }}^3\right)$ and ${\mathrm{Na}}_8$ $\left(14.02\mathrm{}\hspace{0.5em}{\mathrm{\AA }}^3\right)$ are significantally different, the above observation indicates the significance of nonplasmon contributions in the optical spectrum of ${\mathrm{Li}}_8$ and implies that the simple jellium approach and the plasmon pole approximation are not valid for ${\mathrm{Li}}_8.$

We show theoretically that the spectral hole burning recently observed in Brillouin fiber amplifiers and generators can be interpreted without invoking an inhomogeneous broadening of the Brillouin line. By using the three-wave model of stimulated Brillouin scattering (SBS), we first investigate the linear response of a Brillouin fiber amplifier to a weak amplitude modulation of the injected signal wave. The transfer functions that fully characterize this response are analytically calculated. The fact that they may exhibit a dip is shown to be due both to the gain saturation and to the coupling between the pump and signal perturbations that counterpropagate around the steady-state intensity profiles. These transfer functions also appropriately characterize the way through which noisy perturbations are filtered in SBS fiber generators. The spectral hole burning observed in generators is thus simply connected to spectral hole burning studied in SBS amplifiers.

We present an experimental scheme of preparing the tripartite W state via cavity quantum electrodynamics. The discussion of this scheme indicates that it can be realized by current technologies. Also, this scheme can be directly generalized to prepare the general n-qubit W states.

The recent experimental observation of the absolute generalized oscillator strength (GOS) for the Ar $3p-{(4p,4p}^{\prime })$ nondipole transition has been interpreted as a manifestation of quadrupole excitation [X. W. Fan and K. T. Leung, Phys. Rev. A 62, 062703 (2000)]. Contrary to the experimentalists’ assignment, on the grounds of our random-phase-approximation with exchange (RPAE) calculation, we attribute the measured GOS to combined monopole, the dominant component, and quadrupole contributions. Our RPAE GOS’s for the Ar dipole $3p-4s$ and $3p-3d,5s$ and the lowest nondipole transitions are compared with the measurements. The results could have significant implications for other similar transitions, previously interpreted as quadrupole excitation and for interpreting other discrete transitions.

We extract a cold rubidium 85 atomic beam from a magneto-optical trap using the technique based on the pulsed Zeeman-imbalanced radiation pressure. We observe the separation of an atomic beam on a velocity scale associated with the two-photon sub-Doppler resonances in the radiation pressure force, and show that experimental observations are in good agreement with theoretical predictions. We find that under optimal conditions an atomic beam extracted by a homogeneous magnetic field has a longitudinal temperature in a region of $12–30\hspace{0.5em}\mu \mathrm{K},$ which is an order of magnitude lower than the temperatures obtained so far with the magnetic scheme.

We demonstrate that quantum-information processing can be implemented with ions trapped in a far detuned optical cavity. For sufficiently large detuning the system becomes insensitive to cavity decay. Following recent experimental progress, this scheme can be implemented with currently or soon available technology.

We have constructed a two-wire magnetic atom guide incorporating a tapered section, in which the transverse guiding potential steepens as a function of the position along the guide axis. Atoms are slowed as they move into the tapered section and can become reflected. A classical adiabatic model is used to explain the behavior. The model shows and we experimentally observe that the action of the transverse motion, which is an adiabatic invariant, can be used as a control parameter for the atom reflectivity, allowing us to selectively reflect and trap atoms with large transverse action.

We experimentally demonstrate cavity field control by another laser beam with three-level Λ-type atoms inside an optical ring cavity. By adjusting the frequency detuning of the controlling beam (coupled to one of the atomic transitions), the intensity of the cavity field interacting with another atomic transition is switched on and off. Such all-optical switching between two steady states is caused by the enhanced Kerr nonlinearity due to atomic coherence in such system.

Correlations of the type discussed by Einstein, Poldosky, and Rosen in their original 1935 paradox may be generated between the positions and the momenta of two electrons confined in two spatially separated Penning traps when they are allowed to be coupled for a certain time interval. An experimental demonstration of the paradox could be done using the accurate techniques of manipulation and measurement of confined charged particles. The basic ideas presented in this paper might be extended in order to enable quantum information transfer of continuous variables between massive particles.

A generic approach for compiling any classical-block-compression algorithm (which works in bounded space and time) into a quantum-block-compression algorithm is presented. Using this technique, compression asymptotically approaching the von Neumann entropy of a qubit source can be achieved. The automatically compiled algorithms are competitive (in time and space complexity) with hand-constructed quantum-block-compression algorithms.

We investigate theoretically quantum teleportation by means of the number-sum and phase-difference variables. We show that a unitary beam-splitter transformation turns two-mode Fock-states into close-to-maximally entangled states, in this case close approximations of the relative-phase eigenstates. These states could be created experimentally using on-demand single-photon sources, but also with any second-quantized bosonic system (e.g., trapped ions, Bose-Einstein condensates). We show that such “quasi-EPR” states can yield near-unity fidelity for the teleportation of coherent states and of “Schrödinger cat” states.

Experimental and theoretical cross sections for electron-impact excitation of the dipole-allowed transitions ${3s}^2{}^1\overrightarrow{S}3s3p{}^{1}P$ in ${\mathrm{Cl}}^{5+}$ and $3s{}^2\overrightarrow{S}3p{}^{2}P$ in ${\mathrm{Cl}}^{6+}$ near the excitation thresholds are reported. Absolute cross sections are measured using the merged electron-ion beams energy-loss technique. The intermediate-coupling frame-transformation R-matrix method is used to obtain theoretical cross sections. The total cross sections, for the transitions studied in both ions, exhibit resonance structures near threshold. There is excellent agreement between theory and experiment with respect to both the shape and the magnitude of the cross section for the $3s{}^2\overrightarrow{S}3p{}^{2}P$ transition in ${\mathrm{Cl}}^{6+}.$ For ${\mathrm{Cl}}^{5+},$ structures and trends in both the present R-matrix calculation and the previous calculation of Baluja and Mohan [J. Phys. B 20, 831 (1987)] agree well with the experimental results. However, the magnitudes of the theoretical cross sections for ${\mathrm{Cl}}^{5+}$ are significantly smaller than the measured cross section, which has been corrected for metastable contamination.

We investigate the collisional stability of magnetically trapped ultracold molecules, taking into account the influence of magnetic fields. We compute elastic and spin-state-changing inelastic rate constants for collisions of the prototype molecule ${}^{17}{\mathrm{O}}_2$ with a ${}^3\mathrm{He}$ buffer gas as a function of the magnetic field and the translational collision energy. We find that spin-state-changing collisions are suppressed by Wigner’s threshold laws as long as the asymptotic Zeeman splitting between incident and final states does not exceed the height of the centrifugal barrier in the exit channel. In addition, we propose a useful one-parameter fitting formula that describes the threshold behavior of the inelastic rates as a function of the field and collision energy. Results show a semiquantitative agreement of this formula with the full quantum calculations, and suggest useful applications also to different systems. As an example, we predict the low-energy rate constants relevant to evaporative cooling of molecular oxygen.

The treatment of the exchange potential between the bound electrons of a polyatomic target and the continuum electron from the impinging beam employed in single-collision scattering experiments is considered by using different computational approaches. In the relevant experimental setup the impinging electron undergoes single scattering with the gaseous target molecule and only the elastic channel is being considered by the present calculations. The chosen example of the benzene molecule shows that the various modeling of the all-important exchange interaction yield good agreement with the existing experiments and suggest that they could be profitably employed to analyze elastic angular distributions from polyatomic targets of fairly high complexity and fairly large number of bound electrons.

The absorption spectrum of the hydrogen atom in crossed electric and magnetic fields was measured. The magnetic field was set at 6.002 T, and the electric field was fixed at several values from 750 to 1000 V/cm. The observations require several different theoretical methods for their interpretation: (1) The spectrum is “unscaled,” the recurrences are weak, and their periods vary with energy over the interval of the observations. This observation caused us to develop a chirped Fourier transform method to extract closed orbits from the measured spectra. (2) The absorption spectrum consists of quasidiscrete peaks superposed on a smoothly rising continuum. To interpret this observation, a theoretical model of the continuum absorption is created, and we get results consistent with the measurements. (3) The experiments distinguish between “prompt” and “delayed” electrons, corresponding to lifetimes of the excited hydrogen atoms that are, respectively, less than or greater than about 100 ns. (4) At high energies, the measured absorption spectrum contains some regular quasidiscrete states. We use an Einstein-Brillouin-Keller quantization method to identify these as states that lie close to the plane perpendicular to the magnetic field.

The symmetry properties of the Coulomb potential allow for a dynamical spin-1/2 description of any fixed $n$ level of a hydrogenlike atom in a time-dependent sufficiently weak electric and/or magnetic field. An explicit expression for the time dependence of the $l,m$ amplitudes pertaining to a general $n$ level is derived. The derivation follows on purely algebraic operations. Based on the derivation, we give analytical $n$-independent solutions to established and proposed schemes for driving the atom into a high angular-momentum state.

We present a numerical method for generating vortex rings in Bose-Einstein condensates confined in axially symmetric traps. The vortex ring is generated using the line-source approximation for the vorticity, i.e., the curl of the superfluid velocity field is different from zero only on a circumference of a given radius located on a plane perpendicular to the symmetry axis and coaxial with it. The particle density is obtained by solving a modified Gross-Pitaevskii equation that incorporates the effect of the velocity field. We discuss the appearance of density profiles, the vortex core structure, and the vortex nucleation energy, i.e., the energy difference between vortical and ground-state configurations. This is used to present a qualitative description of the vortex dynamics.

By using decoupling and dimension reduction technologies in equations determing the eigenvalue, we solve analytically the coupled hydrodynamic equation for the eigenvalues of collective excitations and obtain analytical expressions for all modes of a Bose-Einstein condensate in anisotropic axially symmetric harmonic traps in the Thomas-Fermi limit.