def _initialize_unitary(self):
        """Set the initial unitary for simulation"""
        self._validate_initial_unitary()
        if self._initial_unitary is None:
            # Set to identity matrix
            self._unitary = np.eye(2 ** self._number_of_qubits,
                                   dtype=complex)
        else:
            self._unitary = self._initial_unitary.copy()
        # Reshape to rank-N tensor
        self._unitary = np.reshape(self._unitary,
                                   self._number_of_qubits * [2, 2])
Set the initial unitary for simulation