  We discuss the unitary quantum dynamics of the Dicke model (spin and
oscillator coupled). A suitable quasiprobabilty representing the quantum state
turns out to obey a Fokker-Planck equation, with drift terms representing the
underlying classical Hamiltonian flow and diffusion terms describing quantum
fluctuations. We show (by projecting the dynamics onto a co-moving Poincar\'e
section) how the interplay of deterministic drift and quantum diffusion
generates equilibration to the microcanonical density, under conditions of
global classical chaos. The pertinent photon statistics reveals macroscopic
quantum fluctuations.
