High-momentum scattering and the condensate fraction

O. K. Harling

MANFRED L. RISTIG, P. M. Lam, J. W. Clark

S. Inouye, A. P. Chikkatur, Dan Stamper-Kurn +3 more

H. A. Gersch, Phil N. Smith

The impulse approximation is used to describe the inelastic cross section for high-energy neutron scattering from superfluid helium in terms of a ground-state momentum distribution of the helium atoms as given by existing variational calculations. The predicted shape of the cross section is compared with recent experimental data and with a previous theory which approximated the noncondensate contribution to the dynamic structure factor by a single-Gaussian function. In contrast to conclusions obtained using the single-Gaussian approximation, our predicted inelastic cross section omitting a condensate contribution provides an acceptable fit to the experimental data. This fit is worsened by introducing a contribution from a condensate fraction in the amount consistent with the variational calculations, namely 11%. If the condensate fraction is arbitrarily reduced from this value, it is found that a much smaller value, with an upper limit of about 3%, is consistent with the available experimental data. It appears that unique assignments of condensate-fraction contributions to inelastic neutron scattering, for the range of neutron energies presently available, will require an improved theory of final-state effects on the shape of the condensate contribution.

Simone Bux, Christine Gnahm, Reinhardt A. W. Maier +2 more

We study collective scattering with Bose-Einstein condensates interacting with a high-finesse ring cavity. The condensate scatters the light of a transverse pump beam superradiantly into modes which, in contrast to previous experiments, are not determined by the geometrical shape of the condensate, but specified by a resonant cavity mode. Moreover, since the recoil-shifted frequency of the scattered light depends on the initial momentum of the scattered fraction of the condensate, we show that it is possible to employ the good resolution of the cavity as a filter selecting particular quantized momentum states.

Paul E. Sokol, Ralph O. Simmons, D. L. Price +1 more

We have measured the momentum distributions in superfluid and normal Helium 4 at identical densities using inelastic neutron scattering as a function of temperature and density. At large enough momentum transfers Q the Impulse Approximation is valid and the single particle momentum distribution n(anti p) can be extracted from the inelastic scattering spectrum. Results are reported. (WHK)