Smoothed Wigner-distributions, decoherence, and the temperature-dependence of the classical-quantum frontier

We discuss the strange behavior at T = 0 of the phase-space Wigner distribution of the harmonic oscillator with the help of the purely quantal concepts of participation ratio of a mixed state and decoherence parameter. We also show that Wigner distribution-smoothing yields interesting insights, specially in the pathological instance in which the Wigner-Fano factor diverges. The associated decoherence parameter also sheds some light on temperature-dependence of the classical-quantum frontier.