Quantum relaxation of multilevel particles

A non-perturbative model of the relaxation of a multilevel particle between collisionally isolated Hilbert subspaces has been developed using the density matrix formalism. The relaxation between these subspaces can be induced by internal state mixing. Under appropriate conditions a particle can be confined inside one subspace even in the case of strong state mixing. The particular case of nuclear spin conversion in CH3F molecules is proposed as a simple and convenient system to study experimentally this type of relaxation for a wide range of parameters.