Abstract

Recently Bose-Einstein condensation (BBC) of ultracold atomic gases has been realized.^1,2 In these experiments the gases are so dilute that only two-body interactions are relevant. As expected, the recent experiments with ⁸⁷Rb and ²³Na showed that BBC of atoms with repulsive interactions, or positive s-wave scattering length, is stable in the two-body interaction regime and is similar in many respects to an ideal gas BEC.¹ However, it is known that ⁷Li has a negative s-wave scattering length,³ corresponding to attractive interactions, so our experiment demonstrating quantum-degenerate conditions with a large number of gaseous ⁷Li atoms was a surprise. It was expected that ⁷Li should undergo an ordinary gas- liquid or gas-solid phase transition before BEC.

© 1996 Optical Society of America