  The Fermi g_F(x,p) function provides a phase space description of quantum
mechanics conceptually different from that based on the the Wigner function
W(x,p). In this paper, we show that for a peaked wave packet the g_F(x,p)=0
curve approximately corresponds to a phase space contour level of the Wigner
function and provides a satisfactory description of the wave packet's size and
shape. Our results show that the Fermi function is an interesting tool to
investigate quantum fluctuations in the semiclassical regime.

Quantum Physics