= Photon polarization
{wiki}
The knowledge that light is polarized precedes the knowledge of the existence of the photon, see <polarization of light> for the classical point of view.
The polarization state and how it can be decomposed into different modes can be well visualized with the <Poincaré sphere>.
One key idea about photon polarization is that it carries <angular momentum>. Therefore, when an electron changes orbitals in the <Schrödinger equation solution for the hydrogen atom>, the angular momentum (as well as energy) change is carried out by the polarization of the <photon>!
\Video[https://www.youtube.com/watch?v=DOENxVgVO5E]
{title=Quantum Mechanics 9b - Photon Spin and Schrodinger's Cat II by ViaScience (2013)}
{description=
* clear animations showing how two circular polarizations can make a vertical polarization
* a <polarizer> can be modelled <bra-ket notation>[bra] operator.
* <light polarization> experiments are extremely direct evidence of <quantum superposition>. Individual photons must be on \i[both] L and R states at the same time because a V filter passes half of either L or R single photons, but it passes \i[all] L + R photons
}
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