Inelastic collisions of atomic antimony, aluminum, erbium and thulium below 1 K.

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Inelastic collision processes driven by anistropic interactions are investigated below 1 K. Three distinct experiments are presented. First, for the atomic species antimony (Sb), rapid relaxation is observed in collisions with 4He. We identify the relatively large spin-orbit coupling as the primary mechanism which distorts the electrostatic potential to introduce significant anisotropy to the ground 4S3/2 state. The collisions are too rapid for the experiment to fix a specific value, but an upper bound is determined, with the elastic-to-inelastic collision ratio γ≤9.1x102. In the second experiment, inelastic mJ-changing and J-changing transition rates of aluminum (Al) are measured for collisions with 3He. The experiment employs a clean method using a single pump/probe laser to measure the steady-state magnetic sublevel population resulting from the competition of optical pumping and inelastic collisions. The collision ratio γ is measured for both mJ- and J-changing processes as a function of magnetic field and found to be in agreement with the theoretically calculated dependence, giving support to the theory of suppressed Zeeman relaxation in spherical 2P1/2 states [1]. In the third experiment, very rapid atom-atom relaxation is observed for the trapped lanthanide rare-earth atoms erbium (Er) and thulium (Tm). Both are nominally nonspherical (L≠0) atoms that were previously observed to have strongly suppressed electronic interaction anisotropy in collisions with helium (γ>104−105,[2,3]). No suppression is observed in collisions between these atoms (γ≲10), which likely implies that evaporative cooling them in a magnetic trap will be impossible. Taken together, these studies reveal more of the role of electrostatic anisotropy in cold atomic collisions.