def state_vector(self, qubit_order: cirq.QubitOrder | None = None) -> np.ndarray:
        """The state-vector representation of this state."""
        from cirq import ops

        if qubit_order is None:
            qubit_order = ops.QubitOrder.DEFAULT
        qubit_order = ops.QubitOrder.as_qubit_order(qubit_order)
        qubits = qubit_order.order_for(self.qubits)

        mat = np.ones(1, dtype=np.complex128)
        for qubit in qubits:
            oneq_state = self[qubit]
            state_vector = oneq_state.state_vector()
            mat = np.kron(mat, state_vector)

        return mat
The state-vector representation of this state.
cirq-core/cirq/value/product_state.py