Expansion of a Bose-Einstein Condensate in an atomic waveguide

The expansion of a Bose-Einstein condensate in an atomic waveguide is analyzed. We study different regimes of expansion, and identify a transient regime between one-dimensional and three-dimensional dynamics, in which the properties of the condensate and its further expansion can be well explained by reducing the transversal dynamics to a two-level system. The relevance of this regime in current experiments is discussed.