DYNAMICS OF A PAIR OF INTERACTING SPINS COUPLED TO AN ENVIRONMENTAL SEA

We solve for the dynamics of a pair of spins, coupled to each other an d also to an environmental sea of oscillators. The environment mediate s an indirect interaction between the spins, causing both mutual coher ence effects and dissipation. This model describes a wide variety of p hysical systems, ranging from 2 coupled microscopic systems (e.g. magn etic impurities, chromophores, etc.), to 2 coupled macroscopic quantum systems. We obtain analytic results for 3 regimes, viz., (i) The ''lo cked'' regime, where the 2 spins lock together; (ii) The ''correlated relaxation'' regime (mutually correlated incoherent relaxation); and ( iii) The ''mutual coherence'' regime, with correlated damped oscillati ons. These results cover most of the parameter space of the system.