title: Global and local relaxation of a spin chain under exact Schrödinger and master-equation dynamics.
abstract: We solve the Schrödinger equation for an interacting spin chain locally coupled to a quantum environment with a specific degeneracy structure. The reduced dynamics of the whole spin chain as well as of single spins is analyzed. We show that the total spin chain relaxes to a thermal equilibrium state independently of the internal interaction strength. In contrast, the asymptotic states of each individual spin are thermal for weak but nonthermal for stronger spin-spin coupling. The transition between both scenarios is found for couplings of the order of 0.1 x deltaE , with deltaE denoting the Zeeman splitting. We compare these results with a master-equation treatment; when time averaged, both approaches lead to the same asymptotic state and finally with analytical results.
authors.affiliation: Institute of Theoretical Physics I, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany. henrich@theo1.physik.uni-stuttgart.de
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Henrich
authors.forename: Mathias
authors.initials: M
authors.lastname: Michel
authors.forename: Michael
authors.initials: M
authors.lastname: Hartmann
authors.forename: Günter
authors.initials: G
authors.lastname: Mahler
authors.forename: Jochen
authors.initials: J
authors.lastname: Gemmer