  The short time dynamics of a quantum Brownian particle in a harmonic
potential is studied in the phase space. An exact non-Markovian analytic
approach to calculate the time evolution of the Wigner function is presented.
The dynamics of the Wigner function of an initially squeezed state is analyzed.
It is shown that virtual exchanges of energy between the particle and the
reservoir, characterizing the non-Lindblad short time dynamics where
system-reservoir correlations are not negligible, show up in the phase space.
