Unlike liquid helium, the trapped atomic gases are inhomogeneous. This gives rise to an unique and almost complete spatial separation between the condensate and above-condensate particles. The separation manifests itself in one of the most exciting features of the JILA experiment. The inhomogeneity also allows the investigation of interaction-related phenomena in spite of the fact that the samples are extremely dilute, with only a few collisions per atom per second. Since, in the absence of interactions, the compressibility of a Bose condensate is infinite, the condensate will be compressed by the trapping potential until the interatomic interactions counterbalance the potential, thus affecting the size and shape of the condensate.
Many intriguing problems await experimental investigation.
Most prominent among them are the relation between BEC and superfluidity, the kinetics of BEC, the size and number dependence of the transition, optical properties, dimensionality aspects, the interaction between two condensates, the use of the condensate as a source for a coherent atomic beam, and the differences with respect to Fermi systems. Similar experiments can be done with 85Rb. There are suggestions that the scattering amplitude of the heavy alkalis can be modified and its sign possibly even changed. Clearly, an exciting period lies ahead. It is fortunate that the results obtained by the group of Cornell and Wieman were realized with methods accessible to many groups in university environments as this will allow a wide exploration of the fascinating Bose-Einstein condensates.