@qml.qnode(dev, interface='tf')
def f(x):
    qml.RX(x, wires=0)
    return qml.expval(qml.PauliZ(0))
@qml.qnode(dev, interface='tf')
def f(x):
    qml.RX(x, wires=0)
    return qml.expval(qml.PauliZ(0))