def _define(self):
        """Calculate a subcircuit that implements this unitary."""
        if self.num_qubits == 1:
            q = QuantumRegister(1, "q")
            angles = euler_angles_1q(self.to_matrix())
            self.definition = [(U3Gate(*angles), [q[0]], [])]
        if self.num_qubits == 2:
            self.definition = two_qubit_kak(self.to_matrix())
Calculate a subcircuit that implements this unitary.