Excitation spectrum of a Bose-Einstein condensate

A measurement of the static structure factor S(k) and the excitation spectrum ω(k) of a Bose-Einstein condensate (BEC), was presented. The excitation spectrum consisted of a linear phonon regime, as well as a single-particle regime and the linear regime provided an upper limit for the superfluid critical velocity, by the Landau criterion. The results showed that the excitation spectrum agreed quantitatively with the Bogoliubov spectrum, in the local density approximation.