Abstract
Temporal coherence is a fundamental property of macroscopic quantum systems, such as lasers in optics and Bose-Einstein condensates in atomic gases and it is a crucial issue for interferometry applications with light or matter waves. Whereas the laser is an “open” quantum system, ultracold atomic gases are weakly coupled to the environment and may be considered as isolated. The coherence time of a condensate is then intrinsic to the system and its derivation is out of the frame of laser theory. Using quantum kinetic theory, we predict that the interaction with noncondensed modes gradually smears out the condensate phase, with a variance growing as at long times , and we give a quantitative prediction for , , and . Whereas the coefficient vanishes for vanishing energy fluctuations in the initial state, the coefficients and are remarkably insensitive to these fluctuations. The coefficient describes a diffusive motion of the condensate phase that sets the ultimate limit to the condensate coherence time. We briefly discuss the possibility to observe the predicted phase spreading, also including the effect of particle losses.
1 More- Received 6 July 2009
DOI:https://doi.org/10.1103/PhysRevA.80.033614
©2009 American Physical Society