Suppression of Zeeman relaxation in cold collisions of 2P1/2 atoms

We present a combined experimental and theoretical study of angular momentum depolarization in cold collisions of 2P atoms in the presence of an external magnetic field. We show that collision-induced Zeeman relaxation of Ga(2P1/2) and In(2P1/2) atoms in cold 4He gas is dramatically suppressed compared to atoms in 2P3/2 states. Using rigorous quantum-scattering calculations based on ab initio interaction potentials, we demonstrate that Zeeman transitions in collisions of atoms in 2P1/2 electronic states occur via couplings to the 2P3/2 state induced by the anisotropy of the interaction potential. Our results suggest the feasibility of sympathetic cooling and magnetic trapping of 2P1/2-state atoms, such as halogens, thereby opening up exciting areas of research in precision spectroscopy and cold-controlled chemistry.