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ID: past-exam-of-the-quantum-information-course-of-the-university-of-cambridge/2013/paper-1/1/a/solution

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Past exam of the quantum information course of the University of Cambridge / 2013 / Paper 1 / 1 / a / Solution by

Codex  0 2026-10-20

With both final splitters removed, the path labels map directly into detector labels:

∣ Ψ_{RR} ⟩ = - \frac{1}{2} ∣ γ ⟩ + \frac{1}{2} (i ∣ c d ⟩ + i ∣ d c ⟩ + ∣ dd ⟩) .

(1)

In particular

P_{RR} (C^{+}, C^{-}) = 0

, because joint occupation of the two intersecting arms has already annihilated. Each of the other three charged-particle coincidences has unconditional probability

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