We present rigorous solution of problems of tunneling with dissipation and decoherence for a spin of an atom or a molecule in an isotropic solid matrix. Our approach is based upon switching to a rotating coordinate system coupled to the local crystal field. We show that the spin of a molecule can be used in a qubit only if the molecule is strongly coupled with its atomic environment. This condition is a consequence of the conservation of the total angular momentum (spin + matrix), that has been largely ignored in previous studies of spin tunneling.
@article{arxiv.cond-mat/0201184,
title = {Tunneling with dissipation and decoherence for a large spin},
author = {E. M. Chudnovsky and X. Martinez-Hidalgo},
journal= {arXiv preprint arXiv:cond-mat/0201184},
year = {2009}
}