Two-photon driven KPO — Schrödinger cat states in phase space
The Kerr parametric oscillator (KPO) has Hamiltonian H = -K ↲Ⲡ+ ε_2(↲ + â²), creating a double-well potential in phase space. The two stable coherent states |+α⟩ and |−α⟩ form the cat qubit logical basis. Phase-flip errors are exponentially suppressed ~ e^{-2|α|²} while bit-flip errors grow polynomially — enabling biased-noise quantum error correction. The Wigner function W(q,p) shows negative regions signaling non-classical correlations.