LOCALIZATION BREAKDOWN AS A JOINT EFFECT OF NONLINEAR AND QUANTUM DISSIPATION

We evaluate the time evolution of sigma(x), the transverse component of a spin-1/2 dipole coupled to an Ohmic bath, using a theory balancing the quantum-mechanical fluctuations of the bath, as depicted by the noninteracting-blip approximation, with the nonlinear dynamics of the discrete nonlinear Schrodinger equation. As a relevant effect of the joint action of these two ingredients, we find that the time evolution of the system does not lead to the localization predicted by some equilibrium analyses. More precisely, starting from an eigenstate of sigma(x), the spin system will never asymptotically reach a broken-symmetry state.