Fig. 2: Frequency shift of the resonance.
From: Tan’s two-body contact across the superfluid transition of a planar Bose gas
Variations of the shift Δν with temperature for various 2D spatial densities. The horizontal error bars represent the statistical uncertainty on the temperature calibration, except for the points at very low temperature (10–22 nK). These ultra-cold points are deeply in the Thomas–Fermi regime, where thermometry based on the known equation of state of the gas is not sensitive enough. The temperature is thus inferred from an extrapolation with an evaporation barrier height of the higher temperature points. The error on the frequency measurement is below 1 Hz and is not shown in this graph. Inset: Variations of the shift Δν with density at low temperature T ~ 22 nK, i.e., a strongly degenerate gas. The straight line is the mean-field prediction corresponding to Δa = −5.7 a0.
