Rowen E E, Bar-Gill N, Davidson N
Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel.
Phys Rev Lett. 2008 Jul 4;101(1):010404. doi: 10.1103/PhysRevLett.101.010404. Epub 2008 Jul 3.
In a Bose-Einstein condensate, the excitation of a Bogoliubov phonon with low momentum (e.g., by a two-photon Bragg process) is strongly suppressed due to destructive interference between two indistinguishable excitation pathways. Here we show that scattering of this sound excitation into a double-momentum mode is strongly enhanced due to constructive interference. This enhancement yields an inherent amplification of second-order sound excitations of the condensate, as we confirm experimentally. We further show that due to parity considerations, this effect is extended to higher-order excitations.
