Time evolution of freely expanded Bose-Einstein condensates containing small numbers of atoms

Abstract

We investigate the time evolution of freely expanded Bose-Einstein condensates by measuring their aspect ratios at different times after their release from a magnetic trap. In these measurements the condensates contain no more than 9000 Rb-87 atoms. By varying the trapping frequency and atom number, we measure the condensate aspect ratios at different expansion times in free space. We compare our measurements with those calculated from the Thomas-Fermi model and a direct numerical solution. Under our trapping condition, the data of the time dependent aspect ratios of the freely expanded condensates reasonably agrees with the numerical calculations, but shows a clear deviation from the predictions of the Thomas-Fermi model when the atom number in the condensates is small.