We complete the program started in  by proving that, in the weak coupling limit, the matrix elements, in the collective coherent vectors, of the Heisenberg evolved of an observable of a system coupled to a quasi-free reservoir through a laser type interaction, converge to the matrix elements of a quantum stochastic process satisfying a quantum Langevin equation driven by a quantum Brownian motion. Our results apply to an arbitrary quasi-free reservoir so, in particular, the finite temperature case is included.
Cite this article
Luigi Accardi, Alberto Frigerio, Yun G. Lu, The Quantum Weak Coupling Limit (II): Langevin Equation and Finite Temperature Case. Publ. Res. Inst. Math. Sci. 31 (1995), no. 4, pp. 545–576DOI 10.2977/PRIMS/1195163914