ROLE OF THE ENVIRONMENT IN CHAOTIC QUANTUM DYNAMICS

We study how the interaction with an external incoherent environment i nduces a crossover from quantum to classical behavior for a particle w hose classical motion is chaotic. Posing the problem in the semiclassi cal regime for weak bath coupling, we find that noise rather than diss ipation is primarily responsible for the dephasing that leads to the q uantum inhibition of mixing. However, the noise is also shown to inhib it the mixing by enhancing paths that interfere coherently.