Excitation of Phonons in a Bose-Einstein Condensate by Light Scattering

thereby “optically imprinting” phonons into the gas. The momentum imparted to the condensate was measured by a time-of-flight analysis. This study is the first to explore phonons with wavelengths much smaller than the size of the trapped sample, allowing a direct connection to the theory of the homogeneous Bose gas. We show the excitation of phonons to be significantly weaker than that of free particles, providing dramatic evidence for correlated momentum excitations in the many-body condensate wave function. In optical Bragg spectroscopy, an atomic sample is illuminated by two laser beams with wave vectors k1 and k2 and a frequency difference v which is much smaller than their detuning D from an atomic resonance. The intersecting beams create a periodic, traveling intensity