[BUG] F.2 code of QFT

[maplexgitx0302]

Node number

Codercise F.2.1, Codercise F.2.3

Expected behavior

The code in F.2.1 and F.2.3

bits = [int(x) for x in np.binary_repr(basis_id, width=dev.num_wires)]

seems not work. This can be simply fixed by

bits = [int(x) for x in np.binary_repr(basis_id, width=num_wires)]

---

Another issue is in the right hand side panel, there is a figure

I think the green and purple initial states (the $|x_0\rangle$ and the $|x_1\rangle$) should also be swapped in the figure. To make the circuit work in this figure, one can test the code by adding additional line

bits = [int(x) for x in np.binary_repr(basis_id, width=num_wires)]

# add this line to make initial state swapped
bits = bits[::-1]

qml.BasisStatePreparation(bits, wires=[0, 1])

Actual behavior

The error pops up when using dev.num_wires

Error: 'DefaultQubit' object has no attribute 'num_wires'

Additional information

No response

Source code

No response

Tracebacks

No response

Check other issues

• I have searched existing GitHub issues to make sure the issue does not already exist.

[alvaro-at-xanadu]

Hello @maplexgitx0302
Thank you so much for reporting this. Strange that this passed the automatic tests 🤔!

This happens because in the newer versions of PennyLane, default.qubit changes the number of wires dynamically according to the paired circuit. It makes sense that it no longer has the num_wires attribute.

We'll push a fix and update!