Measurement of the temperature dependence of the Casimir-Polder force through collective excitations of a Bose-Einstein condensate*

A Rb-87 Bose-Einstein condensate is positioned microns from a dielectric surface and resonantly excited into a mechanical dipole oscillation. Changes in the collective oscillation frequency of the magnetically trapped condensate result from spatial variations in the atom-surface force [1,2]. Recent theoretical work has characterized the temperature dependence of non-equilibrium Casimir-Polder forces [3] in which the temperature of the dielectric surface is different from the temperature of free-space. In our experiment a dielectric surface is heated to 600K while the surrounding environment is kept near room temperature (310K). The magnitude of the Casimir-Polder force is measured in both this non-equilibrium configuration and also in a room temperature equilibrium configuration. Both measurements agree with theoretical predictions, marking the first demonstration of the temperature dependence of the Casimir-Polder force. [1] M. Antezza, L.~P. Pitaevskii and S. Stringari, Phys. Rev. A {\bf 70}, 053619 (2004). [2] D.~M. Harber, J.~M. Obrecht, J.~M. McGuirk and E.~A. Cornell, Phys. Rev. A {\bf 72}, 033610 (2005). [3] M. Antezza, L.~P. Pitaevskii and S. Stringari, Phys. Rev. Lett. {\bf 95}, 113202 (2005).