The Bell state |00 = |00+|112 can be prepared starting with |00 and applying the operation U =C_x(H I). Devise a circuit that takes |00 as input and providees |00 as output using only a C_z gate and global single qubit operations that are applied to both qubits simultaneously. This shows that it is sufficient to act symmetrically on the qubits to produce |00 which is symmetric under qubit exchange.