Date of Award

Spring 1-1-2010

Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Eric A. Cornell

Second Advisor

Debra S. Jin

Third Advisor

Jun Ye


A fluctuating regime associated with the Berenzinskii-Kosterlitz-Thouless (BKT) transition is studied in a two-dimensional system of near-degenerate bosons (87Rb atoms). Two imaging procedures, the in-situ imaging method and the focusing-imaging method, are implemented to image the coordinate-space and momentum-space density distributions. The scaled compressibility is extracted from the coordinate-space density distributions obtained from in-situ images. Comparing the measured compressibility to the prediction from our semiclassical mean-field model, an onset of a regime which is beyond the mean-field prediction is identified and first resolved at phase-space density 2 ≥ 3. Information about the coherence of the system is extracted from the momentum-space distributions obtained from the focusing images. The spatial extent of the coherence at a size of the high density region in the system only appears at a distinguishably higher phase-space density of 2 ≈ 8. Therefore, a very interesting regime that is beyond mean-field prediction, but not yet a condensate, is identified. This regime, which does not exist in three dimensions, is a product of the enhanced interactions associated with reduced dimensionality.