title: Observing the formation of long-range order during Bose-Einstein condensation.
abstract: We have experimentally investigated the formation of off-diagonal long-range order in a gas of ultracold atoms. A magnetically trapped atomic cloud prepared in a highly nonequilibrium state thermalizes and thereby crosses the Bose-Einstein condensation phase transition. The evolution of phase coherence between different regions of the sample is constantly monitored and information on the spatial first-order correlation function is obtained. We observe the growth of the spatial coherence and the formation of long-range order in real time and compare it to the growth of the atomic density. Moreover, we study the evolution of the momentum distribution during the nonequilibrium formation of the condensate.
authors.affiliation: Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: Stephan
authors.initials: S
authors.lastname: Ritter
authors.forename: Anton
authors.initials: A
authors.lastname: Ottl
authors.forename: Tobias
authors.initials: T
authors.lastname: Donner
authors.forename: Thomas
authors.initials: T
authors.lastname: Bourdel
authors.forename: Michael
authors.initials: M
authors.lastname: Köhl
authors.forename: Tilman
authors.initials: T
authors.lastname: Esslinger