Large spin relaxation rates in trapped submerged-shell atoms

Spin relaxation due to atom–atom collisions is measured for magnetically trapped erbium and thulium atoms at a temperature near 500 mK. The rate constants for Er–Er and Tm–Tm collisions are 3.0×10[superscript -10] and 1.1×10[superscript -10] cm[superscript 3] s[superscript -1], respectively, 2–3 orders of magnitude larger than those observed for highly magnetic S-state atoms. This is strong evidence for an additional, dominant, spin relaxation mechanism, electronic interaction anisotropy, in collisions between these “submerged-shell,” L≠0 atoms. These large spin relaxation rates imply that evaporative cooling of these atoms in a magnetic trap will be highly inefficient.National Science Foundation (Grant No. 0757157)Harvard/MIT Center for Ultracold Atom