Bose-Einstein condensation of an atomic gas with attractive interactions

Recently Bose-Einstein condensation (BEC) of ultracold atomic gases was realized. The stability and character of the condensate for atoms with negative scattering length remain tantalizing, open questions, a new challenge for many-body theory. The authors are experimentally investigating these questions using a permanent magnet trap to confine ⁷Li. By evaporative cooling, phase-space densities that are more than 10² times greater than those required for quantum degeneracy can be created. Temperature and density are measured by passing a probe laser beam through the trapped atoms and optically imaging the absorption shadow of the atoms.