Results 1 - 10 of 34919
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[en] The time delay, as defined via phase shifts, does not apply to atom-atom collisions because of the semiclassical nature of the system. In this limit the contribution of one partial wave to the cross section is negligible. Therefore, we analyze time delay for the scattering amplitude and show that some new phenomena may occur, which cannot be explained by the time delay for a single phase shift. The time delay, which is averaged over all scattering angles, shows structure corresponding to several delay mechanisms. We also show that the lifetime of a resonance state, formed in a collision, may be considerably shorter than expected from the theory of resonance scattering
[en] We study the dynamics of a two-component Bose-Einstein condensate where the two components are coupled via an optical lattice. In particular, we focus on the dynamics as one drives the system through a critical point of a first-order phase transition characterized by a jump in the internal populations. Solving the time-dependent Gross-Pitaevskii equation, we analyze the breakdown of adiabaticity, impact of nonlinear atom-atom scattering, and role of a harmonic trapping potential. Our findings demonstrate that the phase transition is resilient to both contact interaction between atoms and external trapping confinement.
[en] An analytical model is considered to the e → c change of Hund's coupling cases in the X(J=1) + Y(1S0) collision of polarized atoms. Deviation from a widely used approximation of a sudden change of the coupling scheme is shown to exceed 10% for realistic interatomic potentials. The proposed analytical model for population redistribution in quasimolecular states that results from passage through a region where the type of coupling changes is in good agreement with the reported numerical calculations for the dispersion interatomic interaction. 27 refs., 4 figs., 2 tabs
[en] Problems of diatomic molecules and atom-atom collisions, in which two identical atoms take part, or nearest-neighbor interactions in hot plasmas require the computations of the electric potential and the electron charge distribution around such a two-centered object. The electric potential around two such identical atoms or ions fulfills special symmetry conditions. These symmetries include a cylindrical symmetry around the line connecting the centers of the two atoms and a reflection symmetry around the plane perpendicular to this line halfway between the two atoms. When the two atoms are far apart, the asymptotic behavior of the charge-state distribution and the potential are those of two separated isolated atoms each of which can be expanded into multipole components around its nucleus. We define a set of new functions Tmk(y,yn) Eq. (2.25), which connect the various multipole components of the electric potential to those of the electron charge distribution in such a two-identical-atom problem, and which take into account all the above symmetry conditions. The great advantage of these transformation functions is the fact that by accounting for the above symmetry conditions, the three-dimensional integration required for the computation of the local electric microfield directly from the Poisson equation is practically reduced to a one-dimensional one. It is shown that the use of these functions greatly reduces the complexity and computation times of problems in which two identical atoms are involved, particularly for high-Z atoms. Explicit exact formulas are given for the computation of the Tmk functions. An example is given which illustrates the use of these functions in first-order perturbation theory. For this special class of problems the procedure presented here results in a closed recursive equation, in which the interatomic distance is the only free parameter
[en] We consider the influence of the inclusion of interatomic interactions on the δ-kicked accelerator model. Our analysis concerns in particular quantum accelerator modes, namely quantum ballistic transport near quantal resonances. The atomic interaction is modeled by a Gross-Pitaevskii cubic nonlinearity, and we address both attractive (focusing) and repulsive (defocusing) cases. The most remarkable effect is enhancement or damping of the accelerator modes, depending on the sign of the nonlinear parameter. We provide arguments showing that the effect persists beyond mean-field description, and lies within the experimentally accessible parameter range
[en] Full text: We use the functional positive-P description of atomic and molecular fields to describe the transfer of atoms from a Bose-Einstein condensate to a molecular condensate, and show that the timescale of the revival of the population transfer is qualitatively different when the mean field approximation is made
[en] We model collisionless collective conversion of a degenerate Fermi gas of atoms into bosonic molecules via a Feshbach resonance, treating the bosonic molecules as a classical field and seeding the pairing amplitudes with random phases. A dynamical instability of the Fermi sea against association with molecules drives the conversion. The model qualitatively reproduces several experimental observations [Regal et al., Nature (London) 424, 47 (2003)]. We predict that the initial temperature of the Fermi gas sets the limit for the efficiency of atom-molecule conversion
[en] The dependence of two-level systems in disordered atomic chain on pressure, both positive and negative was studied numerically. The disorder was produced through the use of interatomic pair potentials having more than one energy minimum. It was found that there exists a correlation between the energy separation of the minima of two-level systems Δ and the variation of this separation with pressure. The correlation may have either positive or negative sign, implying that the asymmetry of two-level systems may in average increase or decrease with pressure depending on the interplay of different interactions between atoms in disordered state. The values of Δ depend on the sign of pressure.