Dimensionality of Dipolar Evaporative Cooling for Degenerate Fermi Gases

Evaporative cooling of Fermi gases is limited by Pauli suppression as the gas becomes increasingly degenerate. However, this suppression scales differently with temperature depending on the dimensionality of the trapped gas, which suggests that certain Fermi systems may have an optimal dimension to perform evaporative cooling. Motivated by collisionally stable molecular gases, we study the collisional thermalization of Fermi gases with long-range dipole-dipole interactions in two dimensions (2D) and three dimensions (3D). Assuming the gas is both in the Wigner threshold regime and below the Fermi temperature, we report scaling laws for the effective elastic to loss cross section in 2D vs. 3D and discuss its implications for efficient evaporative cooling. Using ab initio close coupling calculations for KRb molecules, we show our results have good agreement with recent experimental measurements of an ultracold KRb gas.