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

A normalized bipartite pure state is entangled when it cannot be written as a product state $|a{⟩}_A\otimes |b{⟩}_B$. Equivalently, its Schmidt rank exceeds one. This definition concerns the specified partition into systems A and B; the mixed-state definition of separability requires a different convex-mixture condition.