Schrödinger Cat State
Quantum superposition |ψ⟩ = N(|α⟩ + e^{iφ}|-α⟩) — Wigner function in phase space
Wigner function W(x,p) — interference fringes
Q-function (Husimi) Q(x,p) — smoothed phase space
Cat state = coherent superposition of two coherent states ±α in phase space.
Wigner function: W(x,p) has two Gaussian peaks at ±α PLUS quantum interference fringes at origin.
Decoherence: γt → interference fringes decay as e^{-2|α|²(1-e^{-γt})} — cat "collapses" to mixture.
Negativity of W(x,p) certifies non-classical state. Q-function ≥ 0 always (Husimi, 1940).