Hannover 2010 – scientific programme
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A: Fachverband Atomphysik
A 9: Ultra-Cold Atoms, Ions and BEC II (with Q)
A 9.7: Talk
Wednesday, March 10, 2010, 12:00–12:15, F 303
Gap and screening in Raman scattering of a Bose condensed gas — •Patrick Navez1 and Kai Bongs2 — 1Universitaet Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg, Germany — 2University of Birmingham, Edgbaston, Birmingham, B15 2TT, England
We propose different spectroscopic methods to explore the nature of the thermal excitations of a trapped Bose condensed gas: 1) a four photon process to probe the uniform region in the trap center: 2) a stimulated Raman process in order to analyze the influence of a momentum transfer in the resulting scattered atom momentum distribution. We apply these methods to address specifically the energy spectrum and the scattering amplitude of these excitations in a transition between two hyperfine levels of the gas atoms. In particular, we exemplify the potential offered by these proposed techniques by contrasting the spectrum, expected from the non conserving Bogoliubov approximation valid for weak depletion, to the spectrum of the finite temperature extensions like the conserving generalized random phase approximation (GRPA). Both predict the existence of the Bogoliubov collective excitations but the GRPA approximation distinguishes them from the single atom excitations with a gapped and parabolic dispersion relation and accounts for the dynamical screening of any external perturbation applied to the gas. Two feasible experiments are discussed, one concerns the observation of the gap associated to this second branch of excitations and the other deals with this screening effect. Ref: P. Navez and K. Bongs, Eur. Phys. Lett. (in press).