Gaussian distribution is commonly used as a good approximation to study the trapped one-component Bose-condensed atoms with relatively small nonlinear effect. It is not adequate in dealing with the one-component system of large nonlinear effect, nor the two-component system where phase separation exists. We propose a modified Gaussian distribution which is more effective when dealing with the one-component system with relatively large nonlinear terms as well as the two-component system. The modified Gaussian is also used to study the breathing modes of the two-component system, which shows a drastic change in the mode dispersion at the occurrence of the phase separation. The results obtained are in agreement with other numerical results.

We present a theoretical treatment of conditional preparation of one-photon states from a continuous-wave nondegenerate optical parametric oscillator. We obtain an analytical expression for the output state Wigner function, and we maximize the one-photon state fidelity by varying the temporal mode function of the output state. We show that a higher production rate of high fidelity Fock states is obtained if we condition the outcome on dark intervals around trigger photo detection events.

We examine the role of ground-state coherence on the fluorescence from the excited state in a three-level $\Lambda$ system under continuous-wave excitation. When resonantly pumped, the fluorescence is strongly affected by any perturbation in the ground-state coherent population trapping. From our analytical results, we suggest how to use this strong dependence of fluorescence on the ground-state decays as a new method for the measurement of the ground-state decoherence rates. Our calculations should work well for a wide range of systems such as atomic vapors with a buffer gas, active dopants in solids, and quantum dots, etc. We present a proof of principle experiment using ${}^{87}\mathrm{Rb}$ vapor.

A finite-temperature random-phase approximation (FTRPA) is applied to calculate oscillator strengths for excitations in hot and dense plasmas. Application of the FTRPA provides a convenient, self-consistent method with which to explore coupled-channel effects of excited electrons in a dense plasma. We present FTRPA calculations that include coupled-channel effects. The inclusion of these effects is shown to cause significant differences in the oscillator strength for a prototypical case of ${}^{1}P$ excitation in neon when compared with single-channel and with average-atom calculations. Trends as a function of temperature and density are also discussed.

The effect of a weak uniform magnetic field on the electronic structure of slightly deformed fullerene molecules is studied within the continuum field-theory model. It is shown how the existing fine structure of the electronic energy spectrum due to spheroidal deformation is modified in the presence of a magnetic field. Exact analytical solutions for zero-energy modes are found.

I describe a procedure for calculating thresholds for quantum computation as a function of error model given the availability of ancillae prepared in logical states with independent, identically distributed errors. The thresholds are determined via a simple counting argument performed on a single qubit of an infinitely large Calderbank-Shor-Steane code. I give concrete examples of thresholds thus achievable for both Steane and Knill style fault-tolerant implementations and investigate their relation to threshold estimates in the literature.

We present an experimental demonstration of a modified version of the entanglement-assisted “Guess my Number” protocol for the reduction of communication complexity among three separated parties. The results of experimental measurements imply that the separated parties can compute a function of distributed inputs by exchanging less classical information than by using any classical strategy. And the results also demonstrate the advantages of entanglement-enhanced communication, which is very close to quantum communication. The advantages are based on the properties of Greenberger-Horne-Zeilinger states.

We present an experimental and theoretical investigation of the polarizabilities and hyperfine constants of $D_J$ states in ${}^{133}\mathrm{Cs}$ for $J=3∕2$ and $5∕2$. Experimental values for the hyperfine constant $A$ are obtained from level-crossing signals of the $(7,9,10)D_{5∕2}$ states of ${}^{133}\mathrm{Cs}$ and precise calculations of the tensor polarizabilities ${\alpha }_2$. The results of relativistic many-body calculations for scalar and tensor polarizabilities of the $(5–10)D_{3∕2}$ and $(5–10)D_{5∕2}$ states are presented and compared with measured values from the literature. Calculated values of the hyperfine constants $A$ for these states are also presented and checked for consistency with experimental values.

High-$L$ fine structure patterns in $n=9$ and $n=17$ Rydberg levels of argon have been studied using a Doppler-tuned $\mathrm{C}{\mathrm{O}}_2$ laser and a fast beam of argon atoms. Analysis of the measured pattern using the polarization model yields the scalar dipole polarizability and quadrupole moment of the ${}^{2}P_{3∕2}$ ${\mathrm{Ar}}^{+}$ ion. The results are ${\alpha }_S=6.83\left(8\right)a_0^3$ and $Q=-0.5177\left(15\right)e{a}_0^2$. Within the precision of this study, no vector component of the structure was observed.

We have generalized the BOUND and MOLSCAT packages to allow calculations in basis sets where the monomer Hamiltonians are off diagonal and used this capability to carry out bound-state and scattering calculations on ${}^3\mathrm{He}\text{−}\mathrm{NH}$ and ${}^4\mathrm{He}\text{−}\mathrm{NH}$ as a function of magnetic field. Following the bound-state energies to the point where they cross thresholds gives very precise predictions of the magnetic fields at which zero-energy Feshbach resonances occur. We have used this to locate and characterize two very narrow Feshbach resonances in ${}^3\mathrm{He}\text{−}\mathrm{NH}$. Such resonances can be used to tune elastic and inelastic collision cross sections, and sweeping the magnetic field across them will allow a form of quantum control in which separated atoms and molecules are associated to form complexes. For the first resonance, where only elastic scattering is possible, the scattering length shows a pole as a function of magnetic field and there is a very large peak in the elastic cross section. For the second resonance, however, inelastic scattering is also possible. In this case the pole in the scattering length is dramatically suppressed and the cross sections show relatively small peaks. The peak suppression is expected to be even larger in systems with stronger inelasticity. The results suggest that calculations on ultracold molecular inelastic collisions may be much less sensitive to details of the potential energy surface than has been believed.

We study quantum dynamics of a Bose-Einstein condensate of spin-1 atoms inside a double-well potential. Under the single spatial mode approximation for condensate wave functions localized within each of the two wells, we examine quantum entanglement and pseudo-spin-squeezing properties in both the Rabi and Josephson regimes. Quantum fluctuations is found to be more stable leading to robust multipartite entanglement in the lower end of the Josephson regime, or the mean field self-trapped region. Substantial multipartite entanglement is witnessed not only due to pseudo-spin-squeezing by the axis-twisting interaction but also from redistribution of mode-entangled atoms between the wells by the tunneling coupling.

We consider a polarized Fermi gas in the unitarity limit. Results are calculated analytically up to next-to-leading order in an expansion about $d=4$ spatial dimensions. We find a first order transition from superfluid to normal phase. The critical chemical potential asymmetry for this phase transition is $\delta {\mu }_c=\frac{2\mu }{\epsilon }(1-0.467\epsilon )$, where $\epsilon =4-d$ is the expansion parameter and $\mu$ is the average chemical potential of the two fermion species. Stability of the superfluid phase in the presence of supercurrents is also studied.

We study the single-plane-wave Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) states for BCS-Bose-Einstein condensation crossover at general temperatures $T$. Because we include the important effects of noncondensed pairs, our $T\ne 0$ phase diagrams are different from those reported in earlier work. We find that generalized LOFF phases may be the ground state for a wide range of (weak through moderately strong) interactions, including the unitary regime. However, these LOFF phases are readily destroyed by nonzero $T$.

Measurements of several transitions in krypton carried out with a high-resolution extreme ultraviolet (xuv) laser source in 1987 were recently reanalyzed. This analysis, based on simulating the Doppler-broadened line shape of the iodine reference lines with new, greatly improved iodine reference data, yielded an order-of-magnitude improvement in the agreement between several ${}^{86}\mathrm{Kr}$ transition frequencies between $94.5\mathrm{nm}$ and $116.5\mathrm{nm}\text{to}\pm 5\times 10^{-9}$. The overall relative uncertainty is estimated to be $\pm 6\times 10^{-9}$, which matches the best accuracies achieved in nanosecond short-wavelength experiments. The influence of frequency chirping in the pulsed dye amplifier chain was estimated to be rather low and to vary approximately between $-7.1\mathrm{MHz}$ and $+5.0\mathrm{MHz}$ for the three laser dyes used in this experiment. It is concluded that with an even more careful laser design the chirp-induced frequency shifts could be reduced to less than $1\mathrm{MHz}$. Based on the analysis of the presumable chirp effects a correction for the ${}^{86}\mathrm{Kr}$ atlas by Kaufman and Humphries $-0.05553{\mathrm{cm}}^{-1}$ is determined, which agrees with the result of a very recent two-photon experiment with frequency combs within just $0.00046{\mathrm{cm}}^{-1}$ $\left(14\mathrm{MHz}\right)$, i.e., well within the combined errors of the three data sources involved in the intercomparison.

A spin-polarized beam of photoelectrons of significant intensity from a closed $n{s}^2$-subshell of a spin-aligned atom having a multielectron half-filled subshell in its ground state is predicted. The polarization results from the specific properties of a half-filled shell atom due to the unbalanced exchange interaction between spin-up and spin-down electrons in the atom, both at the independent-particle and multielectron correlation levels. This mechanism causing the preferable spin orientation of outgoing photoelectrons differs from the commonly known mechanisms yielding spin-polarized photoelectrons from atoms. Calculated results for the photoionization of the valence $4s^2$ subshell of a spin-up oriented $\mathrm{Mn}\left(4s^2{}^{6}S\right)$ atom employing spin-polarized Hartree-Fock and random-phase approximation with exchange are presented, but the results are inherent properties of any half-filled subshell atom. The importance of electron correlation effects is emphasized.

We have studied the classical and quantum dynamics of the Morse system driven by time-periodic external field. Floquet energies and Husimi probability distributions of quasibound states of the driven system are obtained using exterior complex scaling method and Floquet theory. As we increase the external field strength, the number of quasibound states is decreased and the Husimi distribution of the quasibound state shows the enhanced positive momentum distribution that appears to be supported by the classical homoclinic tangles that develop on the positive momentum side of the phase space.

We study the dynamics of phase transitions in the one-dimensional Bose-Hubbard model. To drive the system from a Mott insulator to a superfluid phase, we change the tunneling frequency at a finite rate. We investigate the buildup of correlations during fast and slow transitions using variational wave functions, dynamical Bogoliubov theory, Kibble-Zurek mechanism, and numerical simulations. We show that time-dependent correlations satisfy characteristic scaling relations that can be measured in optical lattices filled with cold atoms.

We apply the hyperspherical (HS) method to study a Bose-Einstein condensate in quasi-two-dimensional free space stabilized and confined under the influence of an oscillating magnetic field. The HS method indeed reproduces stabilized breathing mode solutions qualitatively similar to those previously obtained by the Gross-Pitaevskii (GP) equation. Also, the frequencies of our breathing mode solutions are shown to have functional dependence on the physical parameters in a manner similar to the GP results. However, beats in the breathing mode solutions are revealed in the HS approximation, while they are seemingly absent in the GP descriptions. A supplementary analysis of the stationary state solutions shows that the hyperspherical single-particle density exhibits certain characteristic scaling dependence on energy akin to the Townes soliton [Chiao et al., Phys. Rev. Lett. 13, 479 (1964)], but also some difference in detail. The Kapitza averaging leads to an effective time-independent potential and shows how continuously distributed hyperspherical “bound” states turn into discrete “bound” states on accounting of the modulating field. The HS method is made subject to the Floquet analysis in order to interpret the beats in the breathing mode as coherent excitation among discrete Floquet states.