In this article we try to bridge the gap between the quantum dynamical
semigroup and Wigner function approaches to quantum open systems. In particular
we study stationary states and the long time asymptotics for the quantum
Fokker-Planck equation. Our new results apply to open quantum systems in a
harmonic confinement potential, perturbed by a (large) sub-quadratic term.Comment: 19 pages, corrected typos and quoted Theorem 6 more precisel