@qml.qnode(qubit_device_2_wires, interface='tf')
def qf(x):
    qml.RX(x, wires=[0])
    ex = qml.expval(qml.PauliZ(1))
    return (qml.expval(qml.PauliZ(0)), ex)
@qml.qnode(qubit_device_2_wires, interface='tf')
def qf(x):
    qml.RX(x, wires=[0])
    ex = qml.expval(qml.PauliZ(1))
    return (qml.expval(qml.PauliZ(0)), ex)