title: Experimental observation of the Bogoliubov transformation for a Bose-Eeinstein condensed gas.
abstract: Phonons with wave vector q/(planck constant) were optically imprinted into a Bose-Einstein condensate. Their momentum distribution was analyzed using Bragg spectroscopy with a high momentum transfer. The wave function of the phonons was shown to be a superposition of +q and -q free particle momentum states, in agreement with the Bogoliubov quasiparticle picture.
authors.affiliation: Department of Physics, MIT-Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Vogels
authors.forename: K
authors.initials: K
authors.lastname: Xu
authors.forename: C
authors.initials: C
authors.lastname: Raman
authors.forename: J R
authors.initials: JR
authors.lastname: Abo-Shaeer
authors.forename: W
authors.initials: W
authors.lastname: Ketterle