Collisional effects in the dynamics of a dipolar gas

Niccolò Bigagli, Claire Warner, Weijun Yuan +4 more

Stefan S. Natu, Leonard Campanello

Reuben R. W. Wang, John L. Bohn

We discuss the influence of collisions on the dynamics of an ultracold gas whose constituents interact via dipolar forces. This dynamics is governed by the elastic scattering cross section of the molecules, which is to some extent under the experimentalist's control. We compare side-by-side several different situations, highlighting their similarities and differences. These situations are collisions between: 1) point dipoles; 2) electric-field-shielded polar molecules; and 3) microwave-shielded polar molecules, including the effect of microwave ellipticity.

Dajun Wang, Kang-Kuen Ni, Silke Ospelkaus +6 more

Kang-Kuen Ni, Silke Ospelkaus, Dajun Wang +6 more

Yijun Tang, A. G. Sykes, Nathaniel Burdick +3 more

We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.