Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2015 / S3 / 3 / 1 / Solution

The normalized linear polarization state is $|\theta ⟩=\cos \theta |H⟩+\sin \theta |V⟩$. A transmitted-photon count implements the projector $|\theta ⟩⟨\theta |$. The Born rule givesthe single-photon form of Malus's law, assuming ideal polarizers and detection.