Compressibility of an Ultracold Fermi Gas with Repulsive Interactions
  Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters k_F a > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images. 
Ye-Ryoung Lee, Myoung-Sun Heo, Jae-Hoon Choi, Tout T. Wang, Caleb A.   Christensen, Timur M. Rvachov, and Wolfgang Ketterle
cond-mat.quant-gas