Document supported backend filters

[kevinsung]

What is the expected feature or enhancement? At https://qiskit.org/documentation/partners/qiskit_ibm_provider/stubs/qiskit_ibm_provider.IBMProvider.backends.html it says

**kwargs – Simple filters that specify a True/False criteria in the backend configuration, backends status, or provider credentials. An example to get the operational backends with 5 qubits: IBMProvider.backends(n_qubits=5, operational=True)

This gives an example of a simple filter ("operational") but doesn't actually provide a list of supported options.

Acceptance criteria I don't know what this issue template field is for.

[kt474]

The link is documentation for qiskit-ibm-provider but the docstrings of the backends() methods from both repos can be improved.

For **kwargs, as mentioned, any True/False criteria in the backend configuration or attributes (link) can be used - there are too many options to list all of them, but we could add a couple more examples

The filter parameter is similar but not restricted to only a boolean True/False - lambda functions can be used

To see exactly how the filtering is done, we use the filter_backends method in terra.

We'll add a couple more examples to the docstring to make it more clear

[merav-aharoni]

@kt474 - I am a bit confused about the filtering mechanism. Here are my thoughts/observations:

• The filtering as well as the documentation is in several places including qiskit_ibm_provider/ibm_backend_service.py, qiskit_ibm_provider/ibm_provider.py, and twice in qiskit_ibm_runtime/qiskit_runtime_service.py. Wouldn't it make more sense to have the documentation in one place (ibm_backend_service.py) and put references in the other places?
• Also I suggest adding a reference to the documentation of QasmBackendConfiguration in Terra.
• The example with quantum_volume does not work and should be removed.
• My understanding is that in kwargs, it is only possible to pass keys with specific values, so we cannot specify something like max_circuits >100. This can only be done through a lambda function. Am I correct?

[kt474]

@kt474 - I am a bit confused about the filtering mechanism. Here are my thoughts/observations:

• Yes I agree - it would be ideal to have documentation in a central location, but I think it would still be good to have it at least once in each repo
• Sure, I think that would be helpful
• Yes that example can be removed
• Yes that's correct, those filters can only be done through a lambda function