Decoherence and kinetic processes in quantum nanosystems

A quantum master equation has been derived recently by Esposito and Gaspard [Phys. Rev. E 68 (2003) 066112] to study the dynamics of a quantum subsystem weakly interacting with another system which has a dense spectrum. This equation takes into account the fact that, because of energy conservation in the total system, the energy of the system with the dense spectrum is affected by the dynamics of the subsystem. We argue that such a situation can often be encountered in quantum nanosystems and we apply this equation to a nanosystem composed of a spin interacting with some remainder. By doing this, we demonstrate that quantum decoherence may already manifest itself in isolated nanosystems.