title: Equivalence condition for the canonical and microcanonical ensembles in coupled spin systems.
abstract: It is typically assumed, without justification, that a weak coupling between a system and a bath is a necessary condition for the equivalence of a canonical ensemble and a microcanonical ensemble. For instance, in a canonical ensemble, temperature emerges if the system and the bath are uncoupled or weakly coupled. We investigate the validity region of this weak-coupling approximation, using a coupled composite-spin system. Our results show that the spin coupling strength can be as large as the level spacing of the system, indicating that the weak-coupling approximation has a much wider region of validity than usually expected.
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China.
authors.forename: Wenxian
authors.initials: W
authors.lastname: Zhang
authors.forename: C P
authors.initials: CP
authors.lastname: Sun
authors.forename: Franco
authors.initials: F
authors.lastname: Nori