🐛 Regression using qiskit>=0.45.

[burgholzer]

Environment information

• OS: any
• Python version: any
• mqt-qcec version: latest (but could be dating back a bit)
• qiskit version: 0.45.0 (downgrading to qiskit<0.45 resolves the problem)

Description

While looking through the example docs, I noticed that the very simple example shown in the documentation for verifying compilation flows is broken as it reports not_equivalent and emits a warning that both circuits do not operate on the same number of qubits.

After checking the example locally, it turns out that this is a regression in the latest qiskit version. Downgrading qiskit solves the problem. Two things that could be at fault here are the new Singleton Gates or some changes in the _layout attribute.

Expected behavior

Circuits should be considered equivalent (as they always have been).

How to Reproduce

from qiskit import QuantumCircuit, transpile
from qiskit.providers.fake_provider import FakeLondon

from mqt import qcec

circ = QuantumCircuit(3)
circ.x(2)
circ.h(range(3))
circ.ccx(0, 1, 2)
circ.h(range(2))
circ.x(range(2))
circ.h(1)
circ.cx(0, 1)
circ.h(1)
circ.x(range(2))
circ.h(range(2))
circ.measure_all()

optimization_level = 1
circ_comp = transpile(circ, backend=FakeLondon(), optimization_level=optimization_level)

print(qcec.verify_compilation(circ, circ_comp, optimization_level=optimization_level))

[burgholzer]

This seems to have resolved on its own as I can no longer reproduce it and the documentation now also prints equivalent again.