/sup 85/rubidium-a Bose-Einstein condensate with adjustable interactions

Summary form only given. For most values of magnetic field, very cold /sup 85/Rb atoms have a large negative scattering length and large loss rates from magnetic traps. The latter makes it difficult to cool the atoms low enough to achieve Bose-Einstein condensation (BBC), while the former constrains the size of a possible BEC to <100 atoms. However, we have found that near the Feshbach resonance at 154 G the loss rates decrease substantially, and the scattering length can be made positive. We have used these two features to create condensates of several thousand atoms in /sup 85/Rb. We are then able to study the dynamics and loss processes of these condensates as we vary the magnetic field. Small changes in magnetic field give rise to large changes in the magnitude and sign of the self-interaction in the condensate as well as possible couplings to molecular condensates. We will discuss the wide range of behaviors we have observed in this interesting system.