Reduction of the wavepacket: How long does it take?

The reduction of the wavepacket caused by the interaction with the environment occurs on a timescale which is typically many orders of magnitude shorter than the relaxation timescale tau. In particular, it is shown that in a system interacting with a canonical heat bath of harmonic oscillators, decorrelation timescale of two pieces of the wavepacket separated by N thermal de Broglie wavelengths in approximately tau/N(2). Therefore, in the classical limit h bar (YIELDS) O dynamical reversibility (tau - YIELDS infinity) is compatible with instantaneous coherence loss.