An example of pure and mixed states is light polarization. An individual photon can be described as having right or left circular polarization, described by the orthogonal quantum states | R ⟩ ⟩ and | L ⟩ ⟩ or a superposition of the two: it can be in any state α α | R ⟩ ⟩ + β β | L ⟩ ⟩ (with | α α | 2 + | β β | 2 = 1 ), corresponding to linear, circular, or elliptical polarization. Consider now a vertically polarized photon, described by the state | V ⟩ ⟩ = ( | R ⟩ ⟩ + | L ⟩ ⟩ ) / 2 . If we pass it through a circular polarizer that allows either only | R ⟩ ⟩ polarized light, or only | L ⟩ ⟩ polarized light, half of the photons are absorbed in both cases. This may make it seem like half of the photons are in state | R ⟩ ⟩ and the other half in state | L ⟩ ⟩ , but this is not correct: if we pass ( | R ⟩ ⟩ + | L ⟩ ⟩ ) / 2 through a linear polarizer there is no absorption whatsoever, but if we pass either state | R ⟩ ⟩ or | L ⟩ ⟩ half of the photons are absorbed.