Chin Lab at The University of Chicago

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Strongly Interacting Two-Dimensional Bose Gases

Interacting Bose gases in two dimensions provide a platform to study the interplay between interactions, quantum statistics and fluctuations. In this work, we prepare and study strongly interacting two-dimensional Bose gases in the superfluid, the classical Berezenskii-Kosterliz-Thouless (BKT) transition, and the vacuum-to-superfluid quantum critical regimes. By tuning the scattering length and loading the sample into an optical lattice, a wide range (almost two orders of magnitude) of the two-body interaction strength is covered.

Based on the equations of state measurements, we extract the coupling constants as well as critical thermodynamic quantities in different regimes. In the superfluid and the BKT transition regimes, the extracted coupling constants show significant down-shifts from the mean-field and perturbation calculations when g approaches or exceeds one. In the BKT and the quantum critical regimes, all measured thermodynamic quantities show logarithmic dependence on the interaction strength, a tendency confirmed by the extended classical-field and renormalization calculations.

Below are the measured equation of state of 2D Bose gases at different interaction strengths.

Equations of state for 2D Bose gases in the weak and strong coupling regimes. The filled and open circles represent experimental measurements of 2D gases and 2D lattice gases. The upper blue shaded area is the superfluid regime, and the red boundary corresponds to the BKT transition regime. The inset compares the equations of state of a 2D gas and a 2D lattice gas with an almost identical coupling constant g ~ 0.4.

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