Decoherence effects on the tunneling rate of paramagnetic and superparamagnetic particles

We analyze the effects of the environment on the spin tunneling process of paramagnetic and superparamagnetic particles and conclude that the “bare” macroscopic tunneling rate is hardly affected in such case, but others more effective processes come up to change the magnetization state of the particle. We measure the degree of coherence loss by the linear entropy which will account for all correlations present in the process. We conclude that for both, paramagnetic and superparamagnetic particles, the decoherence time scale is extremely short (∼ 10−8..−16s), indicating that coherent tunneling should be strongly suppressed in favor of incoherent tunneling, i.e., the population of higher levels with subsequent decay. Interestingly enough, the ground state tunneling rate is hardly affected by such dissipative mechanisms. However other processes immediately give rise to new (incoherent) possibilities of crossing the barrier.