 Quantum information

Solutions to all three questions of the 11 June 2020 paper. Released Oxford examination archive, member 2019/T/a16608w1.pdf. The dated cover establishes 2020 despite the archive directory. All displayed state vectors are normalized unless described as unnormalized conditional vectors. We use column vectors, $|ij⟩=|i⟩\otimes |j⟩$, and the left tensor factor as the first wire. In a product of gates, the rightmost gate acts first. A global phase is physically irrelevant, but all relative signs and phases below are retained.