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The experimental observation of Beliaev damping in a Bose condensed gas

E. Hodby·O. M. Marago'·G. Hechenblaikner·C. J. Foot
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Abstract

We report the first experimental observation of Beliaev damping of a collective excitation in a Bose-condensed gas. Beliaev damping is not predicted by the Gross-Pitaevskii equation and so this is one of the few experiments that tests BEC theory beyond the mean field approximation. Measurements of the amplitude of a high frequency scissors mode, show that the Beliaev process transfers energy to a lower lying mode and then back and forth between these modes. These characteristics are quite distinct from those of Landau damping, which leads to a monotonic decrease in amplitude. To enhance the Beliaev process we adjusted the geometry of the magnetic trapping potential to give a frequency ratio of 2 to 1 between two of the scissors modes of the condensate. The ratios of the trap oscillation frequencies $ω_y / ω_x$ and $ω_z / ω_x$ were changed independently, so that we could investigate the resonant coupling over a range of conditions.

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E. Hodby, O. M. Marago', G. Hechenblaikner, C. J. Foot. 2000-10-11. The experimental observation of Beliaev damping in a Bose condensed gas. https://doi.org/10.1103/physrevlett.86.2196

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