[BUG] Error in grader

[p-j-r]

Node number

Codercise I.14.2

Expected behavior

IMPLEMENT THE MULTIPLEXER

IF STATE OF FIRST TWO QUBITS IS 01, APPLY X TO THIRD QUBIT

qml.MultiControlledX(control_wires=[0,1], wires=2, control_values='01')
The above code should result in the desired behaviour, that is, give the correct output.

Actual behavior

Incorrect: your circuit does not have the correct action on |01>.

Is however, the error being raised!

Additional information

No response

Source code

No response

Tracebacks

No response

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

[glassnotes]

Hi @p-j-r , thanks for bringing this up! Would you be able to post your full solution code for this problem so I can investigate?

[p-j-r]

[glassnotes]

Hi @p-j-r, the first MultiControlledX has the correct effect on the |01> state, but if you check further down, qml.CRZ(np.pi, wires=[1, 2]) also affects the case where the first two qubits are in |01> since it is a control from wire 1 in state |1> to wire 2; this is why it's saying the results for the |01> case are not correct. If you have any conceptual questions about this, please feel free to ask them on the PennyLane forum and we can discuss in more detail! 🙂

[p-j-r]

Alright, got it. Will work around that. Thank you!

[glassnotes]

No problem, I will close this issue then, feel free to open another if needed!