Quantum enhancement of higher-order phononlike excitations of a Bose-Einstein condensate.
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.
Rowen
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Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel.
Bar-Gill
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Davidson
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