Dipole forces, excitations and dissipation in Bose-Einstein condensates

Summary form only given. A distinguishing feature of Bose-Einstein condensates in trapped atomic gases is the ability to manipulate them with laser light. This is a tool which is not available for the study of liquid helium. In this work, we use the mechanical forces exerted by light on atoms to create and study collective excitations. We can apply either repulsive or attractive forces locally to a Bose-Einstein condensed gas with scanning, focused laser beams tuned to the blue or to the red of the principal atomic resonance, respectively. With spatio-temporal control of the forces, we have studied dissipation in the condensate as well as creating collective excitations with a controllable symmetry and time dependence.