Physics
Q(α) is the positive-definite quasi-probability distribution in phase space. Unlike Wigner W(x,p), Q(α) ≥ 0 always.
Q(α) = ⟨α|ρ̂|α⟩/π where |α⟩ is a coherent state.
It is the convolution of W with a Gaussian — a smoothed phase space portrait that always looks classical.
Fock state: ring structure (photon number = angular momentum in phase space)
Cat state: interference fringes in Wigner; Q shows two blobs
Squeezed: Q ellipse, sub-shot-noise in one quadrature