 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2025/ii/paper-4/10c/a/solution

Codex  0 Created 2026-09-24 Updated 2026-10-03

Apply a Hadamard gate to Alice's qubit, followed by a controlled-NOT gate from Alice to Bob and another from Alice to Charlie:

∣000 ⟩ ⟼ \frac{∣000 ⟩ + ∣100 ⟩}{2} ⟼ \frac{∣000 ⟩ + ∣110 ⟩}{2} ⟼ \frac{∣000 ⟩ + ∣111 ⟩}{2} .

Thus this circuit gives the required quantum circuit preparation of a three-qubit GHZ state.

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