Thermalisation by a boson bath in a pure state

Abstract

We consider a quantum system weakly coupled to a large heat bath of harmonic oscillators. It is well known that such a boson bath initially at thermal equilibrium thermalises the system. We show that assuming a priori an equilibrium state is not necessary to obtain the thermalisation of the system. We determine the complete Schrödinger time evolution of the subsystem of interest for an initial pure product state of the composite system consisting of the considered system and the bath. We find that the system relaxes into canonical equilibrium for almost all initial pure bath states of macroscopically well-defined energy. The temperature of the system asymptotic thermal state is determined by the energy of the initial bath state as the corresponding microcanonical temperature. Moreover, the time evolution of the system is identical to the one obtained assuming that the boson bath is initially at thermal equilibrium with this temperature. A significant part of our approach is applicable to other baths and we identify the bath features which are requisite for the thermalisation studied.

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Cited by in corpus (5)

• Non-equilibrium entangled steady state of two independent two-level systems
• Joule expansion of a pure many-body state
• Ensemble dependence of information-theoretic contributions to the entropy production
• Damped bounces of an isolated perfect quantum gas
• Sudden change of the thermal contact between two quantum systems