DYNAMICS OF A STRONGLY DAMPED 2-LEVEL SYSTEM

Dynamics of a dissipative two-level system is studied using quantum re laxation theory. This calculation goes beyond the commonly used dilute bounce gas approximation (DBGA), even for strong damping. The results obtained here deviate from the DBGA results at low temperatures, howe ver, the DBGA form is recovered at high temperatures. The results in t he parameter regime 1/2 < alpha < 1, where the model has connection wi th the Kondo Hamiltonian, are of particular significance. In this regi me, the spin shows a crossover to a slower exponential relaxation at i ntermediate times, which is roughly half the relaxation rate at short times, as also observed in quantum Monte Carlo simulation of the model . The asymptotic behavior of the spin in the Kondo regime is in agreem ent with the exact conformal field theory results for the Kondo model.