@article {rowenquantum2008,
	title = {Quantum enhancement of higher-order phononlike excitations of a Bose-Einstein condensate.},
	journal = {Physical review letters},
	volume = {101},
	year = {2008},
	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.},
	author = {Rowen, E and Bar-Gill, N and Davidson, N}
}
