Onset of Fokker-Planck dynamics within a Closed Finite Spin System
  Relaxation according to Fokker-Planck equations is a standard scenario in classical statistical mechanics. It is however not obvious how such an equilibration may emerge within a closed, finite quantum system. We present an analytical and numerical analysis of a system comprising sixteen spins in which spatial inhomogeneities of the magnetization relax approximately in accord with a standard Fokker-Planck equation for a Brownian particle in a parabolic potential. 
Hendrik Niemeyer, Daniel Schmidke, Jochen Gemmer
quant-ph cond-mat.stat-mech