The dynamical response of an atomic Bose-Einstein condensate manipulated by an integrated atom-optics device, such as a microtrap or a microfabricated waveguide, is studied. We show that when the miniaturization of the device enforces a sufficiently high condensate density, three-body interactions lead to a spatial modulational instability that results in a fundamental limit on the coherent manipulation of Bose-Einstein condensates.

This work presents a method for the ab initio calculation of isotope shift in atoms and ions with one valence electron above closed shells. As a zero approximation, we use relativistic Hartree-Fock and then calculate correlation corrections. The main motivation for developing the method comes from the need to analyze whether different isotope abundances in early universe can contribute to the observed anomalies in quasar absorption spectra. The current best explanation for these anomalies is the assumption that the fine-structure constant $\alpha$ was smaller at early epoch. We test the isotope-shift method by comparing the calculated and experimental isotope shift for the alkali-metal and alkali-metal-like atoms Na, Mg II, K, Ca II and Ba II. The agreement is found to be good. We then calculate the isotope shift for some astronomically relevant transitions in Si II and Si IV, Mg II, Zn II, and Ge II.

It is shown analytically that there exists a natural basis in terms of which the nonperturbative time evolution of an important class of driven four-level systems in the strong-coupling regime decouples and essentially reduces to the corresponding time evolution in the weak-field regime, exhibiting simple Rabi oscillations between the different relevant quantum states. The predictions of the model are corroborated by an exact numerical calculation.

We predict the presence and positions of purely-long-range bound states of ${}^4\mathrm{He}\left(2s{}^3{S)+}^4\mathrm{He}\right(2p{}^{3}P)$ near the $2s{}^3{S}_1+2p{}^3{P}_{0,1}$ atomic limits. The results of the full multichannel and approximate models are compared, and we assess the sensitivity of the bound states to atomic parameters characterizing the potentials. Photoassociation to these purely-long-range molecular bound states may improve the knowledge of the scattering length associated with the collisions of two ultracold spin-polarized ${}^4\mathrm{He}\left(2s{}^{3}S\right)$ atoms, which is important for the studies of Bose-Einstein condensates.

We investigate the zero-temperature phase diagram of a gas of bosonic atoms in one- and two-color standing-wave lattices in the framework of the Bose-Hubbard model. We first introduce some relevant physical quantities; superfluid fraction, condensate fraction, quasimomentum distribution, and matter-wave interference pattern. We then discuss the relationships between them on the formal level and show that the superfluid fraction, which is the relevant order parameter for the superfluid to Mott-insulator transition, cannot be probed directly via the matter-wave interference patterns. The formal considerations are supported by exact numerical solutions of the Bose-Hubbard model for uniform one-dimensional systems. We then map out the phase diagram of bosons in nonuniform lattices. The emphasis is on optical two-color superlattices which exhibit a sinusoidal modulation of the well depth and can be easily realized experimentally. From the study of the superfluid fraction, the energy gap, and other quantities, we identify additional zero-temperature phases, including a localized and a quasi-Bose-glass phase, and discuss prospects for their experimental observation.

We demonstrate both theoretically and experimentally the manipulation of quantum entangled images, using the coupling between polarization entanglement and the entanglement for the transverse degrees of freedom. Starting from a two-crystal bright source of polarization-entangled photons, we arrive at a configuration in which we are able to prepare superposition states for the down-converted angular spectrum while the polarization superposition state is preserved. This scheme allows us to select the detected quantum image by performing projections onto polarization subspaces. We also demonstrate the potential of the system for applications to quantum cryptography of images.

Real clocks are not perfect. This must have an effect in our predictions for the behavior of a quantum system, an effect for which we present a unified description, encompassing several previous proposals. We study the relevance of clock errors in the Zeno effect and find that generically no Zeno effect can be present (in such a way that there is no contradiction with currently available experimental data). We further observe that, within the class of stochasticities in time addressed here, there is no modification in emission line shapes.

Current-density-functional theory is used to calculate ionization energies of current-carrying atomic states. A recently proposed perturbative approximation to full current-density-functional theory is implemented and found to be numerically feasible. Different parametrizations for the current-dependence of the density functional are critically compared. Orbital currents in open-shell atoms turn out to produce a small shift in the ionization energies. We find that modern density functionals have reached an accuracy at which small current-related terms appearing in open-shell configurations are not negligible anymore, compared to the remaining difference to experiment.

The main purpose of this paper is to derive the capacity of attenuated or amplified noisy quantum channel assisted by two-mode squeezed states. In our previous works, formulas for capacity and reliability function have been obtained for continuous variable communication channel in the case where the classical information is conveyed by unentangled quantum Gaussian states. This paper investigates how two-mode squeezed states can enhance classical communication over quantum Gaussian channel.

We investigate the synthesis of continuous-variable two-mode unitary gates in the setting where two modes A and B are coupled by a fixed quadratic Hamiltonian $H.\mathrm{}$ The gate synthesis consists of a sequence of evolutions governed by Hamiltonian $H,$ which are interspaced by local phase shifts applied to A and $B.\mathrm{}$ We concentrate on protocols that require the minimum number of necessary steps and we show how to implement the beam splitter and the two-mode squeezer in just three steps. Particular attention is paid to Hamiltonian $x_A{p}_B$ that describes the effective off-resonant interaction of light with the collective atomic spin.

It is shown that the system of two three-level atoms in the $\Lambda$ configuration in a cavity can evolve into a long-lived maximum entangled state if the Stokes photons vanish from the cavity by means of either leakage or damping. The difference in the evolution picture corresponding to the general model and effective model with two-photon process in a two-level system is discussed.

Asymptotic forms of the scattered wave for a system of three arbitrary charged particles valid in all domains relevant to breakup are derived. The derivations are based on the relationship between the total wave function of a breakup process in a three-body system with Coulomb interactions and the wave function of the process of scattering of all three particles of the system in the continuum. The results are free from amplitude-phase ambiguity problems associated with previously known forms. A similar technique is used to obtain asymptotic forms of the three-body Coulomb Green’s function.

For the K-shell decay, magnesium is the first element in the periodic table which shows cascading transitions. We investigated the whole cascade of magnesium by using the photoelectron-photoion coincidence technique on the $1s,$ $2s,$ and $2p$ decay. The experimentally determined and calculated decay probabilities for the ${1s}^{-1},$ the ${2s}^{-1},$ and the ${2p}^{-1}$ decay, i.e., the whole cascade, are in good agreement with each other. For the calculation of higher final ionic charge states, it was found that electron correlations have to be taken into account. The fluorescence yields for the K and L shell and the Coster-Kronig factor for the L shell were determined.

The multiple-ionization and coupling effects in L-shell ionization of atoms by heavy-ion impact have been studied by measuring the L x-ray production cross sections in solid targets of Au, Bi, Th, and U bombarded by oxygen ions in the energy range 6.4–70 MeV. The measured L x-ray spectra were analyzed using the recently proposed method accounting for the multiple-ionization effects, such as x-ray line shifting and broadening, which enables one to obtain the ionization probabilities for outer shells. The L-subshell ionization cross sections have been obtained from measured x-ray production cross sections for resolved $L{\alpha }_{1,2},$ $L{\gamma }_1,$ and $L{\gamma }_{2,3}$ transitions using the L-shell fluorescence and Coster-Kronig yields being substantially modified by the multiple ionization in the M and N shells. In particular, the effect of closing of strong $L_1-L_3{M}_{4,5}$ Coster-Kronig transitions in multiple-ionized atoms was evidenced and discussed. The experimental ionization cross sections for the $L_1,$ $L_2,$ and $L_3$ subshells have been compared with the predictions of the semiclassical approximation (SCA) and the ECPSSR theory that includes the corrections for the binding-polarization effect within the perturbed stationary states approximation, the projecticle energy loss, and Coulomb deflection effects as well as the relativistic description of inner-shell electrons. These approaches were further modified to include the L-subshell couplings within the “coupled-subshell model” (CSM). Both approaches, when modified for the coupling effects, are in better agreement with the data. Particularly, the predictions of the SCA-CSM calculations reproduce the experimental L-subshell ionization cross section reasonably well. Remaining discrepancies are discussed qualitatively, in terms of further modifications of the L-shell decay rates caused by a change of electronic wave functions in multiple-ionized atoms.

A magnetic octupole filter set in a $90°$ curve produces $\approx {10}^8$ cold Rb atoms/s by filtering low-velocity particles from a thermal source. We measure the speed distribution of Rb exiting the filter to be 3.5 K using a Rydberg-atom time-of-flight scheme in which Rb is excited via the process $5s{}^2{S}_{1/2}\to 5p{}^2{P}_{3/2}^o\to 32d{}^{2}D.\mathrm{}$ We develop a general theory of the transmission and speed distribution of particles emitted from such a source including nonadiabatic effects. A detailed Monte Carlo simulation using the theory accurately reproduces the experimental results. We show that for Cs, Li, and Rb atoms and ${\mathrm{S}}_2$ molecules, nonadiabatic effects do not dramatically effect the performance of the filter, and that the output flux temperatures for a wide variety of filter configurations are well fit to a simple functional form.

We analyze both analytically and numerically the resonant four-wave mixing of two co-propagating single-photon wave packets. We present analytic expressions for the two-photon wave function, and show that quantum solutions exist which display a shape-preserving oscillatory exchange of excitations between the modes. Potential applications including quantum-information processing are discussed.

We compare remote quantum information concentration by a Greenberger-Horne-Zeilinger (GHZ) state with an unlockable bound entangled state. We find that in view of communication security the bound entangled state works better than the GHZ state.

It was reported that Bose-Einstein condensation induces a spontaneous magnetization in spinor bosons. This phenomenon is called Bose-Einstein ferromagnetism (BEF). We propose a phenomenological model consistent with the prediction of BEF and show that BEF might be attributed to the intrinsic magnetic moment of particles. Taking BEF into account, the phase diagram of an optically trapped spinor condensate is reexamined.