 Solution

ID: past-exam-of-the-computer-science-course-of-the-university-of-oxford/2021/quantum-information/2/a/i/solution

Factor the sum before making an entanglement claim:

∣Φ ⟩ = \frac{1}{2} (∣ + ⟩ + ∣ - ⟩) \otimes (∣0 ⟩ + ∣1 ⟩) = ∣0 ⟩ \otimes ∣ + ⟩ .

The state is not entangled: it is a product state. A sum written with several tensor-product terms need not be entangled; those terms may combine into a single tensor product.

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