The momentum distribution function for the two-component 1D gases of bosons and fermions is studied in the limit of strong interatomic repulsion. A pronounced reconstruction of the distribution is found at a temperature much smaller than the Fermi temperature. This new temperature scale, which equals the Fermi temperature divided by the dimensionless coupling strength, is a feature of the two-component model and does not exist in the one-component case. We estimate the parameters relevant for the experimental observation of the crossover effect.

We present a simple method to include the effects of diffraction into the description of a light-atomic ensemble quantum interface in the context of collective variables. Carrying out a scattering calculation we single out the purely geometrical effect and apply our method to the experimental relevant case of Gaussian-shaped atomic samples stored in single beam optical dipole traps probed by a Gaussian beam. We derive simple scaling relations for the effect of the interaction geometry and compare our findings to the results from one-dimensional models of light propagation.

The ionization dynamics of a xenon cluster with 40 atoms is analyzed under a pump-probe scenario of laser pulses where an infrared laser pulse of 50-fs length follows with a well-defined time delay a vuv pulse of the same length and peak intensity. The mechanism of resonant energy absorption due to the coincidence of the ir laser frequency with the frequency of collective motion of quasifree electrons in the cluster is mapped out by varying the time delay between the pulses.

A Markovian wave-function collapse model is presented where the collapse-inducing operator, constructed from quantum fields, is a manifestly covariant generalization of the mass-density operator utilized in the nonrelativistic continuous spontaneous localization (CSL) wave-function collapse model. However, the model is not Lorentz invariant because two such operators do not commute at spacelike separation, i.e., the time-ordering operation in one Lorentz frame, the “preferred” frame, is not the time-ordering operation in another frame. However, the characteristic spacelike distance over which the commutator decays is the particle’s Compton wavelength so, since the commutator rapidly gets quite small, the model is “almost” relativistic. This quasirelativistic CSL (QRCSL) model is completely finite: unlike previous, relativistic, models, it has no (infinite) energy production from the vacuum state. QRCSL calculations are given of the collapse rate for a single free particle in a superposition of spatially separated packets, and of the energy production rate for any number of free particles: these reduce to the CSL rates if the particle’s Compton wavelength is small compared to the model’s distance parameter. One motivation for QRCSL is the realization that previous relativistic models entail excitation of nuclear states which exceeds that of experiment, whereas QRCSL does not; an example is given involving quadrupole excitation of the ${}^{74}\mathrm{Ge}$ nucleus.

We use the x-ray extended-range technique (XERT) [Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of molybdenum in the x-ray energy range of $13.5–41.5\mathrm{keV}$ to 0.02–0.15 % accuracy. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct where necessary a number of experimental systematic errors. These results represent the most extensive experimental data set for molybdenum and include absolute mass attenuation coefficients in the regions of the x-ray absorption fine structure (XAFS) and x-ray-absorption near-edge structure (XANES). The imaginary component of the atomic form-factor $f_2$ is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1–15 % persist between the calculated and observed values.

The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of ${\mathrm{Pb}}_n(n=2\text{–}22)$ clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed.

Spectroscopic studies of few-body systems at ultracold temperatures provide valuable information that often cannot be extracted in a hot environment. Considering a pair of atoms, we propose a cooling mechanism that makes use of a scattering Feshbach resonance. Application of a series of time-dependent magnetic field ramps results in either zero, one, or two atoms remaining trapped. If two atoms remain in the trap after the field ramps are completed, then they have been cooled. Application of the proposed cooling mechanism to optical traps or lattices is considered.

The viscous relaxation time of a trapped two-component gas of fermions in its normal phase is calculated as a function of temperature and scattering length, with the collision probability being determined by an energy-dependent $s$-wave cross section. The result is used for calculating the temperature dependence of the frequency and damping of collective modes studied in recent experiments, starting from the kinetic equation for the fermion distribution function with mean-field effects included in the streaming terms.

We perform a comparative study of the finite temperature behavior of ultracold Bose atoms in optical lattices by the slave fermion and the slave boson approaches to the Bose-Hubbard model. The phase diagram of the system is presented. Although both approaches are equivalent without approximations, the mean field theory based on the slave fermion technique is quantitatively more appropriate. Conceptually, the slave fermion approach automatically excludes the double occupancy of two identical fermions on the same lattice site. By comparing to known results in limiting cases, we find the slave fermion approach better than the slave boson approach. For example, in the non-interacting limit, the critical temperature of the superfluid-normal liquid transition calculated by the slave fermion approach is closer to the well-known ideal Bose gas result. At zero-temperature limit of the critical interaction, strength from the slave fermion approach is also closer to that from the direct calculation using a zero-temperature mean field theory.

The full set of stationary states of the mean field of a Bose-Einstein condensate in the presence of a potential step or pointlike impurity are presented in closed analytic form. The nonlinear Schrödinger equation in one dimension is taken as a model. The nonlinear analogs of the continuum of stationary scattering states, as well as evanescent waves, are discussed. The solutions include asymmetric soliton trains and other wave functions of intriguing form, such as a pair of dark solitons bound by an impurity.

The properties of all-optical phase-coherent frequency division by 2, based on a self-phase-locked continuous-wave (cw) optical parametric oscillator (OPO), are investigated theoretically. The coupled field equations of an OPO with intracavity quarter-wave plate are solved analytically in steady-state, yielding a condition for self-phase-locked operation. In the self-phase-locked state, two different values for the pump power at threshold are obtained. By using a linear stability analysis, it is proven that only the lower threshold value is stable, whereas the higher threshold value is unstable. The analytical investigations of the steady-state field values further reveal a twofold symmetry in phase space. The theoretical consideration is completed by a numerical analysis based on the integration of the envelopes of the three OPO fields, which allows for studying the temporal evolution of different initial values. The numerical investigation of the OPO subharmonic phases shows that the two-phase eigenstates are equivalent with respect to experimental parameters and are assumed by the self-phase-locked OPO in dependence of the initial phases of the subharmonic fields, dividing phase space into two symmetric basins of attraction.

We investigate control schemes for the dynamics of a collection of dipole-interacting three-level atoms in $\mathrm{V}$- or $\mathrm{\Lambda }$- configuration. For this, we discuss the strong-field steady-state behavior of these systems under the influence of external parameters such as the relative phase between the two applied strong driving laser fields, the ratio of spontaneous decay and incoherent pumping rates, the splitting frequency between closely spaced atomic states, or a surrounding thermal bath. We show that these may act as convenient tools to sensitively control the collective dynamics of the atoms. As applications, we analyze the fluorescence and absorption properties of the atomic samples. Finally, we discuss the transient behavior to show that the presented schemes feature a rapid system evolution as required for many applications.

The differential-phase-shift quantum key distribution (DPS-QKD) is a recently proposed QKD scheme in which a pulse train is transmitted through a quantum channel. This paper extends the ideal of the DPS-QKD to entanglement-based systems. Two schemes are presented. In one, an entanglement source sends pulse trains of signal and idler to two parties (Alice and Bob), respectively, who phase-modulate the incoming pulses and receive them after one-bit delay interferometers. In the other, two entanglement sources are prepared, one between Alice and a repeating node (Charlie) and one between Charlie and Bob, which send signal and idler pulse trains to Alice and Bob and Charlie, respectively. These schemes offer a longer distance between Alice and Bob than the conventional DPS-QKD.

The QED contribution to the energies of the circular $(n,\ell =n-1)$, $2⩽n⩽13$, transitions have been calculated for several kaonic atoms throughout the periodic table, using the current world-average kaon mass. Calculations were done in the framework of the Klein-Gordon equation, with finite nuclear size, finite particle size, and all-order Uelhing vacuum polarization corrections, as well as Källén and Sabry and Wichmann and Kroll corrections. These energy level values are compared with other computed values. The circular transition energies are compared with available measured and theoretical transition energies. Electron screening is evaluated using a Dirac-Fock model for the electronic part of the wave function. The effect of electronic wave-function correlation is evaluated.

Photoionization of the first excited $p$ states of the $\mathrm{Be}$-like ${\mathrm{B}}^{+}$ ion, which interact with the even-parity continua, has been studied theoretically. The calculated photoionization cross sections contain a number of autoionizing Rydberg series of resonances converging to the ${\mathrm{B}}^{2+}$ $2p$, $3s$, $3p$, and $3d$ states. Lower members of the Rydberg series of resonances with $n⩽12$ are identified and resonance positions $E_r$, effective quantum numbers $n^{*}$, and widths $\Gamma$ are presented. Excellent agreement between length- and velocity-gauge results is found, along with overall good agreement with previous work.

This paper is devoted to the study of the dynamics of two weakly coupled Bose-Einstein condensates confined in a double-well trap and perturbed by random external forces. The energy diffusion due to random forcing is quantitatively analyzed. The energy distribution is shown to evolve to a stationary distribution which depends on the initial state of the condensate only through the total number of atoms. This loss of memory of the initial conditions allows a simple and complete description of the stationary dynamics of the condensate. In particular, when the number of atoms exceeds a threshold value, the condensate temporarily localizes into one of the wells and jumps into the other well according to a Markovian dynamics. This localization occurs even in the presence of dissipation.

We analyze quantum field models of the bosenova experiment, in which ${}^{85}\mathrm{Rb}$ Bose-Einstein condensates were made to collapse by switching their atomic interactions from repulsive to attractive. Specifically, we couple the lowest order quantum field correlation functions to the Gross-Pitaevskii function, and solve the resulting dynamical system numerically. Comparing the computed collapse times with the experimental measurements, we find that the calculated times are much larger than the measured values. The addition of quantum field corrections does not noticeably improve the agreement compared to a pure Gross-Pitaevskii theory.

The interaction of two spatially separated impurity atoms through phonon exchange in a Bose-Einstein condensate is studied within a Bogoliubov approach. The impurity atoms are held by deep and narrow trap potentials and experience level shifts which consist of a mean-field part and vacuum contributions from the Bogoliubov phonons. In addition, there is a conditional energy shift resulting from the exchange of phonons between the impurity atoms, which can be employed for a transfer of quantum information between the atoms.

We study the diffraction of atoms and weakly bound three-atomic molecules from a transmission grating at non-normal incidence. Due to the thickness of the grating bars, the slits are partially shadowed. Therefore, the projected slit width decreases more strongly with the angle of incidence than the projected period, increasing, in principle, the experimental resolution. The shadowing, however, requires a revision of the theory of atom diffraction. We derive an expression in the style of the Kirchhoff integral of optics and show that the diffraction pattern exhibits a characteristic asymmetry which must be accounted for when comparing with experimental data. We then analyze the diffraction of weakly bound trimers and show that their finite size manifests itself in a further reduction of the slit width by $(3∕4)⟨r⟩$ where $⟨r⟩$ is the average bond length. The improved resolution at non-normal incidence may in particular allow us to discern, by means of their bond lengths, between the small ground state of the helium trimer [$⟨r⟩\approx 1\mathrm{nm}$, Barletta and Kievsky, Phys. Rev. A 64, 042514 (2001)] and its predicted Efimov-type excited state ($⟨r⟩\approx 8\mathrm{nm}$, ibid.), and in this way to experimentally prove the existence of this long-sought Efimov state.

We present doubly differential cross sections for single and multiple ionization of the outer shell of neon by $750\mathrm{eV}$ electron impact. The distinction between single and multiple ionization was achieved by performing a charge state analysis of the recoil ions in coincidence with forward scattered, energy analyzed electrons. By a comparison to photon impact data, the contribution of the second-order double ionization mechanism is estimated and found to be neglible at this impact energy. Following a similar procedure adopted by J. A. R. Samson [Phys. Rev. Lett. 65, 2861 (1990)], the importance of the first-order TS-1 double ionization mechanism is also estimated. As a result it is found that for large energy losses shakeoff is the dominant double ionization mechanism.