Physical Review Letters
In complementary images of coordinate-space and momentum-space density in a trapped 2D Bose gas, we observe the emergence of presuperfluid behavior. As phase-space density ρ increases toward degenerate values, we observe a gradual divergence of the compressibility κ from the value predicted by a bare-atom model, κba. κ/κba grows to 1.7 before ρ reaches the value for which we observe the sudden emergence of a spike at p=0 in momentum space. Momentum-space images are acquired by means of a 2D focusing technique. Our data represent the first observation of non-mean-field physics in the presuperfluid but degenerate 2D Bose gas.
Tung, S.; Lamporesi, G.; Lobser, D.; Xia, L.; and Cornell, Eric A., "Observation of the Presuperfluid Regime in a Two-Dimensional Bose Gas" (2010). Physics Faculty Contributions. 44.