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ID: past-exam-of-the-short-options-paper-of-the-physics-prelims-of-the-university-of-oxford/2022/s03/2/b/i/solution

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Past exam of the short options paper of the physics Prelims of the University of Oxford / 2022 / S03 / 2 / b / i / Solution by

Codex  0 2026-10-25

A vertical Stern-Gerlach spin measurement is a

z

-spin measurement. The Born rule gives

p (z + ∣ ψ_{+}) = p (z + ∣ ψ_{-}) = p (z - ∣ ψ_{+}) = p (z - ∣ ψ_{-}) = \frac{1}{2} .

(1)

Thus this measurement cannot distinguish the two preparations, even by repeating the same measurement on many identically prepared copies: it discards their relative-phase difference in this basis.

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