Probing the thermal atoms of a Bose gas through Raman transition

Abstract

We explore the many body physics of a Bose condensed atom gas at finite temperature through the Raman transition between two hyperfine levels. Unlike the Bragg scattering where the phonon-like nature of the collective excitations has been observed, a different branch of thermal atom excitation is found theoretically in the Raman scattering. This excitation is predicted in the generalized random phase approximation (GRPA) and has a gapped and parabolic dispersion relation. The gap energy results from the exchange interaction and is released during the Raman transition. The scattering rate is determined versus the transition frequency $\omega$ and the transferred momentum $\vc{q}$ and shows the corresponding resonance around this gap. Nevertheless, the Raman scattering process is attenuated by the superfluid part of the gas. The macroscopic wave function of the condensate deforms its shape in order to screen locally the external potential displayed by the Raman light beams. This screening is total for a condensed atom transition in order to prevent the condensate from incoherent scattering. The experimental observation of this result would explain some of the reasons why a superfluid condensate moves coherently without any friction with its surrounding.

18 pages, 6 figures, Topical Issue on Novel Quantum Phases and Mesoscopic Physics in Quantum Gases

References in corpus (5)

• Goos-Hänchen-Like Shifts in Atom Optics
• Collective Excitations of a Two-Component Bose Condensate at Finite Temperature
• Ground states of hard-core bosons in one dimensional periodic potentials
• Collisionless dynamics of the condensate predicted in the random phase approximation
• Manifestation of a gap due to the exchange energy in a spinor condensate

Cited by in corpus (1)

• Gap and screening in Raman scattering of a Bose condensed gas