Anisotropic rethermalization in ultracold thermal dipolar gases

Understanding the thermalization dynamics in ultracold gases is essential for its use in evaporative cooling and studies of many-body physics. In a dipolar thermal gas, it is primarily collisions which serve to facilitate thermalization, made intricate by their anisotropic differential cross section. We present theoretical methods to characterize the number of collisions per rethermalization [1], which for dipolar gases, are highly dependent on the dipole alignment axis. These methods are formulated to be easily applied in experimental contexts, and even reduce to analytic expressions if the route to thermal equilibrium is assumed as a single exponential decay. In the analytic case, collisional rethermalization is fully characterized by the dipole magnitude and orientation, scattering length, and excitation geometry. We characterize the extent to which our expressions are valid and compare their stipulated behavior to Monte Carlo simulations. 

[1] C. R. Monroe, E. A. Cornell, C. A. Sackett, C. J. Myatt,and C. E. Wieman, Phys. Rev. Lett. 70, 414 (1993).