title: Quantum enhancement of higher-order phononlike excitations of a Bose-Einstein condensate.
abstract: 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.
authors.affiliation: Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: E E
authors.initials: EE
authors.lastname: Rowen
authors.forename: N
authors.initials: N
authors.lastname: Bar-Gill
authors.forename: N
authors.initials: N
authors.lastname: Davidson