Free-fall expansion of finite-temperature Bose-Einstein condensed gas in the non-Thomas-Fermi regime

We report on our study of the free-fall expansion of a finite-temperature Bose-Einstein condensed cloud of 87Rb. The experiments are performed with a variable total number of atoms while keeping constant the number of atoms in the condensate. The results provide evidence that the Bose-Einstein condensate dynamics depends on the interaction with thermal fraction. In particular, they provide experimental evidence that the thermal cloud compresses the condensate. (fast track communication)