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 Incoming links: Polarization state

The normalized linear polarization state is

∣ θ ⟩ = cos θ ∣ H ⟩ + sin θ ∣ V ⟩

. A transmitted-photon count implements the projector

∣ θ ⟩ ⟨ θ ∣

. The Born rule gives

p (θ) = ∣ ⟨ θ ∣ H ⟩ ∣^{2} = cos^{2} θ,

the single-photon form of Malus's law, assuming ideal polarizers and detection.