Resonances and W.K.B. theory.

Shachar Klaiman, Ido Gilary

Frederick R. Manby, Graham Doggett

A theory of electronic resonances based on spin-coupled wavefunctions is presented. The formulation is state selective and yields the best single-configurational minimax wavefunctions for resonance closed channels. The theory is demonstrated by calculations of positions, shifts and widths of resonances of a test system, s-wave helium.

S. J. J. M. F. Kokkelmans, J. N. Milstein, R. Walser +2 more

Summary form only given. For non-resonant atomic interactions the properties of ultra-cold scattering can be accurately represented by the scattering length. When the interactions are resonant, for instance when the atoms are colliding via a Feshbach resonance, the scattering properties become strongly dependent on energy, and the scattering length approximation is no longer valid. We show that there is a limited set of parameters that fully characterizes the scattering in the ultra-cold regime, and that this description can be easily incorporated into a theory of many-body physics. In effect, it can be shown that with a Hamiltonian where the resonant bound-state is explicitly treated, the resulting many-body mean-field equations have built in the microscopic two-body coupled-channels scattering equations. We have used this many-body theory to derive a theory of resonance superfluidity, and applied it to both fermionic /sup 40/K and /sup 6/Li. Since the scattering length a does not appear as an expansion parameter of the theory it can be shown that this field theory does not break down as a goes to infinity. In fact, the theory describes the high-T/sub c/ behavior of the system and predicts a critical temperature which can be as high as half the Fermi temperature.

D. Klakow, M. Weber, P.‐G. Reinhard

Արթուր Մելիքյան, S. G. Saakyan

A theory is developed of resonant second harmonic generation in a medium consisting of three-level atoms (molecules). Reduced equations for wave propagation are solved without expanding a nonlinear polarization as a series in powers of the field intensities, so that the theory is applicable also to strong resonances. The case of a strong two-photon resonance is investigated and it is shown how the results differ from those obtained using the conventional theory which applies to the nonresonance cases. It is shown that the proposed theory can be generalized to the processes of generation of sum and difference frequencies.

Earle H. Kennard, Fritz Reiche, H. Stafford Hatfield +1 more