Phys. Rev. A 68, 053611 (2003) [16 pages]Bogoliubov sound speed in periodically modulated Bose-Einstein condensatesReceived 11 August 2003; published 19 November 2003 We study the Bogoliubov excitations of a Bose-condensed gas in an optical lattice having arbitrary spatial dimensions. Of primary interest is the long-wavelength phonon dispersion for both current-free and current-carrying condensates. We obtain the phonon sound speed by carrying out a systematic expansion of the Bogoliubov equations in powers of the phonon wave vector. Our result for the current-carrying case agrees with the one recently obtained by means of a hydrodynamic theory. © 2003 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.68.053611
DOI:
10.1103/PhysRevA.68.053611
PACS:
03.75.Kk, 03.75.Lm, 05.30.Jp, 67.40.Db
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