Effects of a quantum heat bath on the dynamics of a nonlinear subsystem: reduced density matrix approach Original Research Article

The investigation of a reaction field induced nonlinear subsystem dynamics coupled to a quantum heat bath is presented. Projection technique along with time-convolutionless treatment of the total Liouville equation is applied and a new reduced nonlinear dissipative Liouville (RNDL) equation for the subsystem dynamics is derived. It is shown that the new RNDL equation, due to the reaction field nonlinearity, contains besides the coherent nonlinear and standard dissipative terms also an extra dissipative term which mediates the bath influence on the subsystem dynamics over the reaction field nonlinear coupling. The approach presented describes correctly quantum effects and the description is not restricted to limiting temperature regimes. The application of the method to the degenerate symmetric nonlinear dimer with Ohmic intersite coupling to the quantum heat bath has revealed that in the long-time limit the effect of the nonlinearity, with the tendency for localization in the intermediate time regime, is destroyed. The subsystem is driven to the thermodynamic equilibrium with a symmetric steady state.