Cooling by Spontaneous Decay of Highly Excited Antihydrogen Atoms in Magnetic Traps

An efficient cooling mechanism of magnetically trapped, highly excited antihydrogen (H̅ ) atoms is presented. This cooling, in addition to the expected evaporative cooling, results in trapping of a large number of H̅ atoms in the ground state. It is found that the final fraction of trapped atoms is insensitive to the initial distribution of H̅ magnetic quantum numbers. Expressions are derived for the cooling efficiency, demonstrating that magnetic quadrupole (cusp) traps provide stronger cooling than higher order magnetic multipoles. The final temperature of H̅ confined in a cusp trap is shown to depend as ∼2.2T_n0n₀^-2/3 on the initial Rydberg level n₀ and temperature T_n0.