Quantum measurement and decoherence - art. no. 032101

Distribution functions defined in accordance with the quantum theory of mea surement are combined with results obtained from the quantum Langevin equat ion to discuss decoherence in quantum Brownian motion. Closed form expressi ons for wave packet spreading and the attenuation of coherence of a pair of wave packets are obtained. The results are exact within the context of lin ear passive dissipation. It is shown that, contrary to widely accepted curr ent belief, decoherence can occur at high temperature in the absence of dis sipation. Expressions for the decoherence time with and without dissipation are obtained that differ from those appearing in earlier discussions.