Collisions at nanokelvin temperatures in Bose-Einstein condensates

Bose-Einstein condensed atomic gases are a new class of quantum fluids. They are produced by cooling a dilute atomic gas to nanokelvin temperatures using laser and evaporative cooling techniques. In this paper we review developments in Bose-Einstein condensation, emphasizing how this new quantum fluid has become a laboratory for the study of collisions at ultralow energy and of collective effects in light-atom and atom-atom interactions. Magnetic fields have been used to modify the scattering length for atomic collisions. Spinor condensates were created, with a spin structure determined by spin relaxation collisions and external magnetic fields. We have used light scattering to study collective excitations and observed superradiant light emission. Dissipation was studied by dragging a repulsive, blue-detuned laser beam through the fluid, as well as by inducing collisions between condensates.