Past exam of the mathematics course of the University of Cambridge / 2024 / ii / Paper 4 / 10E / b / iv / Solution

Alice performs the operation and measurement from part (iii) and sends the one-bit outcome to Bob. If the bit is $0$, Bob does nothing. If it is $1$, Bob applies $ZX$, which maps $|{\psi }_2⟩$ to $|{\psi }_1⟩$ by part (i). In either case Bob finishes with the known target state $|{\psi }_1⟩$, using one shared Bell pair and one classical bit.