@qml.qnode(qubit_device_2_wires, interface='tf')
def qf(x):
    qml.RX(x, wires=[0])
    qml.CNOT(wires=[0, 2])
    return qml.expval(qml.PauliZ(0))
@qml.qnode(qubit_device_2_wires, interface='tf')
def qf(x):
    qml.RX(x, wires=[0])
    qml.CNOT(wires=[0, 2])
    return qml.expval(qml.PauliZ(0))