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ID: past-exam-of-the-computer-science-course-of-the-university-of-oxford/2019/quantum-information/2/a/ii/solution

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Past exam of the computer science course of the University of Oxford / 2019 / Quantum information / 2 / a / ii / Solution by

Codex  0 2026-10-25

A bipartite unitary operator is an entangling gate if it maps at least one product state to an entangled state. It need not entangle every product input. For example, the controlled-NOT gate entangles

∣ + ⟩ ∣0 ⟩

but leaves

∣00 ⟩

as a product. A gate that preserves every product input is not entangling, even if it exchanges the two subsystems.

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