Charge transfer and coherence dynamics of a tunnelling system coupled to an harmonicoscillator

Abstract

We study the transition probability and coherence of a two-site system, interacting with anoscillator. Both properties depend on the initial preparation. The oscillator is prepared in athermal state and, even though it cannot be considered as an extended bath,it produces decoherence because of the large number of states involved in thedynamics. In the case in which the oscillator is initially displaced, a coherentdynamics of charge entangled with oscillator modes takes place. Coherency is,however, degraded as far as the oscillator mass increases, producing an increasinglylarge recoherence time. Calculations are carried on by exact diagonalization andcompared with two semiclassical approximations. The role of the quantum effectsare highlighted in the long time dynamics, where semiclassical approaches giverise to a dissipative behaviour. Moreover, we find that the oscillator dynamicshas to be taken into account, even in a semiclassical approximation, in orderto reproduce a thermally activated enhancement of the transition probability.