Stable Rb-85 Bose-Einstein condensates with widely tunable interactions

Bose-Einstein condensation has been achieved in a magnetically trapped samp le of Rb-85 atoms. Long lived condensates of up to 10(4) atoms have been pr oduced by using a magnetic-field-induced Feshbach resonance to reverse the sign of the scattering length. This system provides new opportunities for t he study of condensate physics. The variation of the scattering length near the resonance has been used to magnetically tune the condensate self-inter action energy over a wide range, extending from strong repulsive to large a ttractive interactions. When the interactions were switched from repulsive to attractive, the condensate shrank to below our resolution limit; and aft er similar to 5 ms emitted a burst of high-energy atoms.