Critical Behavior of a Trapped Interacting Bose Gas
T. Donner,1
S. Ritter,1
T. Bourdel,1
A. Öttl,1
M. Köhl,1,2*
T. Esslinger1
The phase transition of Bose-Einstein condensation was studied
in the critical regime, where fluctuations extend far beyond
the length scale of thermal de Broglie waves. We used matter-wave
interference to measure the correlation length of these critical
fluctuations as a function of temperature. Observations of the
diverging behavior of the correlation length above the critical
temperature enabled us to determine the critical exponent of
the correlation length for a trapped, weakly interacting Bose
gas to be

= 0.67 ± 0.13. This measurement has direct
implications for the understanding of second-order phase transitions.
1 Institute of Quantum Electronics, Eidgenössische Technische Hochschule (ETH) Zürich, CH-8093 Zürich, Switzerland.
2 Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
* To whom correspondence should be addressed. E-mail: koehl{at}phys.ethz.ch