Quantum quasi-probability distribution W(x, p)
The Wigner function W(x,p) = (1/πℏ)∫ψ*(x+y)ψ(x−y)e^(2ipy/ℏ)dy is the closest quantum analog to a classical phase-space distribution. Coherent states give Gaussian blobs; Fock states |n⟩ show n nodal rings; Schrödinger cat states (superposition of ±α) display quantum interference fringes between the two lobes. Negative values are a signature of non-classical states.