Direct observation of growth and collapse of a Bose-Einstein condensate with attractive interactions

Quantum theory predicts that Bose-Einstein condensation of a spatially homo geneous gas with attractive interactions is precluded by a conventional pha se transition into either a liquid or solid(1). When confined to a trap, ho wever, such a condensate can form(2), provided that its occupation number d oes not exceed a limiting value(3,4). The stability limit is determined by a balance between the self-attractive fortes and a repulsion that arises fr om position-momentum uncertainty under conditions of spatial confinement. N ear the stability limit, self-attraction can overwhelm the repulsion, causi ng the condensate to collapse(5-8). Growth of the condensate is therefore p unctuated by intermittent collapses(9,10) that are triggered by either macr oscopic quantum tunnelling or thermal fluctuation. Previous observations of growth and collapse dynamics have been hampered by the stochastic nature o f these mechanisms. Here we report direct observations of the growth and su bsequent collapse of a Li-7 condensate with attractive interactions, using phase-contrast imaging. The success of the measurement lies in our ability to reduce the stochasticity in the dynamics by controlling the initial numb er of condensate atoms using a two-photon transition to a diatomic molecula r state.