= Interferometric polarization tomography
A <polarizing beam splitter> converts a <photon polarization> <qubit> to two paths. Rotating one arm's <photon polarization> to match the other and recombining at a balanced <beam splitter> gives $P_1(\theta)=1/2+\operatorname{Re}(\alpha^*\beta e^{i\theta})$. Measurements at phases zero and $\pi/2$ recover the transverse <Bloch vector> components; direct counts in the two separated arms recover the population difference. All three components, rather than a fringe alone, determine an arbitrary <photon polarization> <density matrix>.
// Target: quantum-theory.bigb
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