The excitation spectrum of a Bose-Einstein condensate

Summary form only given. The excitation spectrum of a Bose-Einstein condensate should give much insight into this system. For wavelengths much shorter than the radius of the condensate, the excitation spectrum is an essentially continuous function, which characterizes the intrinsic bulk properties of the condensate Previously, isolated points on the excitation spectrum and their dependence on the chemical potential were measured We report the first measurement of the excitation spectrum, as well as the static structure factor.