Role of attractive interactions on Bose-Einstein condensation.

The physical properties and stability of a trapped Bose{Einstein condensate are strongly innuenced by the presence of a net attractive interaction between the particles. In this Letter we describe the spatial distribution, stability, collisional loss rates, and lifetimes for this situation in a weakly interacting trapped atomic gas in the context of mean eld theory. The experimentally important case of 7 Li is discussed in some detail. We show how the condensate contracts and the mean eld becomes unstable as the number of atoms in the condensate are increased. We further show how the number of atoms is limited by the rapid increase in collisional loss rates associated with the contraction of the condensed atomic cloud.