Electron attachment to SF6 and lifetimes of SF6- negative ions

We study the process of low-energy electron capture by the SF6 molecule. Our approach is based on the model of Gauyacq and Herzenberg [J. Phys. B 17, 1155 (1984)] in which the electron motion is coupled to the fully symmetric vibrational mode through a weakly bound or virtual s state. By tuning the two free parameters of the model, we achieve an accurate description of the measured electron attachment cross section and good agreement with vibrational excitation cross sections of the fully symmetric mode. An extension of the model provides a limit on the characteristic time of intramolecular vibrational relaxation in highly-excited SF6-. By evaluating the total vibrational spectrum density of SF6-, we estimate the widths of the vibrational Feshbach resonances of the long-lived negative ion. We also analyse the possible distribution of the widths and its effect on the lifetime measurements, and investigate nonexponential decay features in metastable SF6-.Comment: 22 pages, 10 figures, submitted to Phys. Rev.

Counterintuitive transitions in the multistate Landau-Zener problem with linear level crossings

We generalize the Brundobler-Elser hypothesis in the multistate Landau-Zener problem to the case when instead of a state with the highest slope of the diabatic energy level there is a band of states with an arbitrary number of parallel levels having the same slope. We argue that the probabilities of counterintuitive transitions among such states are exactly zero.Comment: 9 pages, 5 figure

Making Cold Molecules by Time-dependent Feshbach Resonances

Pairs of trapped atoms can be associated to make a diatomic molecule using a time dependent magnetic field to ramp the energy of a scattering resonance state from above to below the scattering threshold. A relatively simple model, parameterized in terms of the background scattering length and resonance width and magnetic moment, can be used to predict conversion probabilities from atoms to molecules. The model and its Landau-Zener interpretation are described and illustrated by specific calculations for $^{23}$Na, $^{87}$Rb, and $^{133}$Cs resonances. The model can be readily adapted to Bose-Einstein condensates. Comparison with full many-body calculations for the condensate case show that the model is very useful for making simple estimates of molecule conversion efficiencies.Comment: 11 pages, 11 figures; talk for Quantum Challenges Symposium, Warsaw, Poland, September 4-7, 2003. Published in Journal of Modern Optics 51, 1787-1806 (2004). Typographical errors in Journal article correcte

Scalar and Spinor Particles with Low Binding Energy in the Strong Stationary Magnetic Field Studied by Means of Two-and Three-Dimensional Models

On the basis of analytic solutions of Schrodinger and Pauli equations for a uniform magnetic field and a single attractive $\delta({\bf r})$-potential the equations for the bound one-active electron states are discussed. It is vary important that ground electron states in the magnetic field essentially different from the analog state of spin-0 particles that binding energy has been intensively studied at more then forty years ago. We show that binding energy equations for spin-1/2 particles can be obtained without using of a well-known language of boundary conditions in the model of $\delta$-potential that has been developed in pioneering works. Obtained equations are used for the analytically calculation of the energy level displacements, which demonstrate nonlinear dependencies on field intensities. It is shown that in a case of the weak intensity a magnetic field indeed plays a stabilizing role in considering systems. However the strong magnetic field shows the opposite action. We are expected that these properties can be of importance for real quantum mechanical fermionic systems in two- and three-dimensional cases.Comment: 18 page

Atom-Atom Scattering Under Cylindrical Harmonic Confinement: Numerical and Analytical Studies of the Confinement Induced Resonance

In a recent article [M. Olshanii, Phys. Rev. Lett. {\bf 81}, 938 (1998)], an analytic solution of atom-atom scattering with a delta-function pseudopotential interaction in the presence of transverse harmonic confinement yielded an effective coupling constant that diverged at a `confinement induced resonance.' In the present work, we report numerical results that corroborate this resonance for more realistic model potentials. In addition, we extend the previous theoretical discussion to include two-atom bound states in the presence of transverse confinement, for which we also report numerical results hereComment: New version with major revisions. We now provide a detailed physical interpretation of the confinement-induced resonance in tight atomic waveguide

Field of homogeneous Plane in Quantum Electrodynamics

We study quantum electrodynamics coupled to the matter field on singular background, which we call defect. For defect on the infinite plane we calculated the fermion propagator and mean electromagnetic field. We show that at large distances from the defect plane, the electromagnetic field is constant what is in agreement with the classical results. The quantum corrections determining the field near the plane are calculated in the leading order of perturbation theory.Comment: 16 page

Low-energy three-body dynamics in binary quantum gases

The universal three-body dynamics in ultra-cold binary Fermi and Fermi-Bose mixtures is studied. Two identical fermions of the mass $m$ and a particle of the mass $m_1$ with the zero-range two-body interaction in the states of the total angular momentum L=1 are considered. Using the boundary condition model for the s-wave interaction of different particles, both eigenvalue and scattering problems are treated by solving hyper-radial equations, whose terms are derived analytically. The dependencies of the three-body binding energies on the mass ratio $m/m_1$ for the positive two-body scattering length are calculated; it is shown that the ground and excited states arise at $m/m_1 \ge \lambda_1 \approx 8.17260$ and $m/m_1 \ge \lambda_2 \approx 12.91743$, respectively. For m/m_1 \alt \lambda_1 and m/m_1 \alt \lambda_2, the relevant bound states turn to narrow resonances, whose positions and widths are calculated. The 2 + 1 elastic scattering and the three-body recombination near the three-body threshold are studied and it is shown that a two-hump structure in the mass-ratio dependencies of the cross sections is connected with arising of the bound states.Comment: 16 page

Backward scattering of low-energy antiprotons by highly charged and neutral uranium: Coulomb glory

Collisions of antiprotons with He-, Ne-, Ni-like, bare, and neutral uranium are studied theoretically for scattering angles close to 180$^{\circ}$ and antiproton energies with the interval 100 eV -- 10 keV. We investigate the Coulomb glory effect which is caused by a screening of the Coulomb potential of the nucleus and results in a prominent maximum of the differential cross section in the backward direction at some energies of the incident particle. We found that for larger numbers of electrons in the ion the effect becomes more pronounced and shifts to higher energies of the antiproton. On the other hand, a maximum of the differential cross section in the backward direction can also be found in the scattering of antiprotons on a bare uranium nucleus. The latter case can be regarded as a manifestation of the screening property of the vacuum-polarization potential in non-relativistic collisions of heavy particles.Comment: 14 pages, 5 figure

Control of Ultra-cold Inelastic Collisions by Feshbash Resonances and Quasi-One-Dimensional Confinement

Cold inelastic collisions of atoms or molecules are analyzed using very general arguments. In free space, the deactivation rate can be enhanced or suppressed together with the scattering length of the corresponding elastic collision via a Feshbach resonance, and by interference of deactivation of the closed and open channels. In reduced dimensional geometries, the deactivation rate decreases with decreasing collision energy and does not increase with resonant elastic scattering length. This has broad implications; e.g., stabilization of molecules in a strongly confining two-dimensional optical lattice, since collisional decay of the highly vibrationally excited states due to inelastic collisions is suppressed. The relation of our results with those based on the Lieb-Liniger model are addressed.Comment: 5 pages, 1 figur