**Input:** Two entangled qubits in Bell state $|\Phi^{+}\rangle = \frac{1}{\sqrt{2}} \big(|00\rangle + |11\rangle\big)$.

**Goal:** Change the two-qubit state to $|\Phi^{-}\rangle = \frac{1}{\sqrt{2}} \big(|00\rangle - |11\rangle\big)$.
