Collective enhancement and suppression in dilute Bose-Einstein condensates

The coherent and collective nature of a Bose-Einstein condensate can enhance or suppress physical processes. Bosonic stimulation enhances scattering in already occupied states which leads to matter wave amplification, and the suppression of dissipation leads to superfluidity. In this summer school notes we present several experiments where enhancement and suppression have been observed and discuss the common roots of and differences between these phenomena. sheet and suddenly released. A series of phase-contrast images (upper part) and time-of-flight absorption images display the collision. The phase contrast pictures show the spreading of the upper condensate during acceleration, its collision, and merging with the stationary cloud. The time-of-flight pictures represent the velocity distribution. Before the scattering event, there were two distinct peaks representing the accelerated and the stationary condensate. After the collision, only one cloud was left which was heated up by the collision.