  We show that the effective coarse graining of a two-mode squeezed density
matrix, implicit in the Wehrl approaches to a semiclassical phase-space
distribution, leads to results in agreement with previous different definitions
of entropy for the process of pair production from the vacuum. We also present,
in this context, a possible interpretation of the entropy growth as an
amplification (due to the squeezing) of our lack of knowledge about the initial
conditions, which gives rise to an effective decoherence of the squeezed
density matrix.
