CORRELATION IN THE LANGEVIN THEORY OF BROWNIAN-MOTION

In a paper with the same title as the above, Manoliu and Kittel calcul ated the high temperature ensemble average of the nonequal time produc t of the displacement and random force in the classical Brownian motio n problem. Here, using a generalized quantum Langevin equation (GLE), we generalize these considerations to the quantum case and to the case of an arbitrary heat bath (such as, e.g., the blackbody radiation hea t bath). Also, we consider an arbitrary temperature and we generalize beyond Brownian motion to the case of a harmonically bound particle in a heat bath. In addition, we point out that correlations of the type considered are widely used in many applications in a variety of differ ent areas of physics and we review some recent applications of the GLE .