Relaxation and Decoherence
In all solutions of the generalized spin precession equation studied so far, the components of the density matrix were either constant or exhibited an oscillatory behavior. In reality, however, every oscillation will eventually be damped out, and after some time the system will return to its thermal equilibrium, a process called relaxation. A perturbation approach within second order approximation leads to the remarkable result that each rank of tensor polarization decays with its own relaxation time constant. A similar result is obtained with a stochastic relaxation model in which relaxation is due to jump diffusion. The book concludes with a discussion of decoherence and its distinction from relaxation.