Spontaneous parametric down-conversion process can split photons into type II photon pairs with mutually perpendicular polarization. Part of a series of articles about Quantum mechanics {\displaystyle i\hbar {\frac {\partial }{\partial t}}|\psi (t)\rangle ={\hat {H}}|\psi (t)\rangle } {\displaystyle i\hbar {\frac {\partial }{\partial t}}|\psi (t)\rangle ={\hat {H}}|\psi (t)\rangle } Schrödinger equation Introduction Glossary History Background[show] Fundamentals[hide] Coherence Decohere