Theory of elementary excitations in unstable Bose-Einstein condensates

U. Leonhardt, T. Kiss, P. Ohberg

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Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of elementary excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the noncondensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to sonic horizons - sonic black and white holes. For sonic white holes the spectrum of unstable modes turns out to be intrinsically discrete, whereas black holes may be stable.
Original languageEnglish
JournalPhysical Review A
Issue number3
Publication statusPublished - 2003


  • soft condensed matter
  • bose-einstein
  • fluids
  • physics

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