Simulator method of FakeBackends changes num qubits in configuration

[chriseclectic]

Informations

• Qiskit Aer version: 0.12
• Python version: 3.9
• Operating system: MacOs

What is the current behavior?

When using AerSimulator.from_backend information such as the coupling map is taken from the backend, however if the simulation method is changed to "stabilizer", the number of qubits is set to a value larger than the coupling map.

Steps to reproduce the problem

backend = AerSimulator.from_backend(FakeMontreal(), method=method)
backend.configuration().num_qubits

Returns 10000 for stabilizer, 63 for extended stabilizer, 32 for statevector, 16 for density matrix.

In this case the fake backend has 27 qubits in its coupling map.

What is the expected behavior?

The number of qubits in the configuration should be set to the number of qubits in a coupling map if the coupling map is not None.

Suggested solutions