From single-particle excitations to sound waves in a box-trapped atomic Bose-Einstein condensate

Abstract

We experimentally and theoretically investigate the lowest-lying axial excitation of an atomic Bose-Einstein condensate in a cylindrical box trap. By tuning the atomic density, we observe how the nature of the mode changes from a single-particle excitation (in the low-density limit) to a sound wave (in the high-density limit). Throughout this crossover the measured mode frequency agrees with Bogoliubov theory. Using approximate low-energy models we show that the evolution of the mode frequency is directly related to the interaction-induced shape changes of the condensate and the excitation. Finally, if we create a large-amplitude excitation, and then let the system evolve freely, we observe that the mode amplitude decays non-exponentially in time; this nonlinear behaviour is indicative of interactions between the elementary excitations, but remains to be quantitatively understood.

arXiv comment6 pages, 5 figures

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• Quantum Gases in Optical Boxes
• Universal Sound Diffusion in a Strongly Interacting Fermi Gas
• Beyond Lee-Huang-Yang description of self-bound Bose mixtures
• Exact Results for the Boundary Energy of One-Dimensional Bosons
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• An Equation of State for Turbulence in the Gross-Pitaevskii model
• Metastability, chaos and spectrum tomography for Bose-Hubbard rings and chains