Solution

ID: past-exam-of-the-introduction-to-quantum-information-course-of-the-university-of-oxford/2021/3/b/solution

No: the advertised pure joint state is incompatible with these marginals. Their eigenvalue multisets are and , which differ. Part a shows that a bipartite pure state must give the same nonzero Schmidt spectrum on both sides.
This excludes Eve's purity claim, not every possible joint state or every possibility of entanglement. A mixed state can have unequal marginal spectra; the product , for example, has exactly the stated marginals.

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