Abstract

We report on the experimental demonstration of the impact of dipole-dipole interactions on the excitations of a dilute quantum gas. We precisely measure the frequency of one the quadrupolar vibration modes of a trapped chromium BEC [1, 2]. The frequency of this mode is shifted when the orientation of the atom spin with respect to the trap axes is changed. The agreement with previous theoretical predictions [3] is excellent. Furthermore, comparison of our experimental outcomes with new theoretical predictions [1] sheds light on the range of validity of the Thomas-Fermi approach at limited atom numbers and demonstrates how the study of BEC excitations is a sensitive probe of dipolar interactions. We are currently setting up a Bragg spectroscopy scheme to extend this work to the measurement of the excitation spectrum in the phonon regime. At the conference, we will report on the status of this experimental search for an anisotropic effect on the sound velocity.

© 2011 IEEE