AerSimulator.from_backend() does not work with qiskit_aer 0.13.0

[mmartinsantamaria]

Informations

• Qiskit Aer version: 0.13.0
• Python version: 3.11.4
• Operating system: macOS 11.7.10

What is the current behavior?

When the next code is executed:

from qiskit_ibm_provider import IBMProvider
from qiskit_aer import AerSimulator

provider=IBMProvider()
backend=provider.get_backend("ibm_nairobi")
backend=AerSimulator.from_backend(backend)

The next error appears:

KeyError                                  Traceback (most recent call last)
File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/qiskit/providers/models/backendconfiguration.py:383, in QasmBackendConfiguration.__getattr__(self, name)
    382 try:
--> 383     return self._data[name]
    384 except KeyError as ex:

KeyError: 'description'

The above exception was the direct cause of the following exception:

AttributeError                            Traceback (most recent call last)
Cell In[3], line 3
      1 #Consigo imitar las características del computador real
      2 #utilizando el método from_backend
----> 3 backend_aer=AerSimulator.from_backend(backend)

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/qiskit_aer/backends/aer_simulator.py:843, in AerSimulator.from_backend(cls, backend, **options)
    840         options["noise_model"] = noise_model
    842 # Initialize simulator
--> 843 sim = cls(configuration=configuration, properties=properties, **options)
    844 return sim

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/qiskit_aer/backends/aer_simulator.py:706, in AerSimulator.__init__(self, configuration, properties, provider, **backend_options)
    702 # Cache basis gates since computing the intersection
    703 # of noise model, method, and config gates is expensive.
    704 self._cached_basis_gates = self._BASIS_GATES["automatic"]
--> 706 super().__init__(
    707     configuration, properties=properties, provider=provider, backend_options=backend_options
    708 )

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/qiskit_aer/backends/aerbackend.py:75, in AerBackend.__init__(self, configuration, properties, defaults, backend_options, provider)
     70 configuration.simulator = True
     71 configuration.local = True
     72 super().__init__(
     73     provider=provider,
     74     name=configuration.backend_name,
---> 75     description=configuration.description,
     76     backend_version=configuration.backend_version,
     77 )
     79 # Initialize backend properties and pulse defaults.
     80 self._properties = properties

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/qiskit/providers/models/backendconfiguration.py:385, in QasmBackendConfiguration.__getattr__(self, name)
    383     return self._data[name]
    384 except KeyError as ex:
--> 385     raise AttributeError(f"Attribute {name} is not defined") from ex

AttributeError: Attribute description is not defined

Steps to reproduce the problem

This only happens with qiskit_aer 0.13.0, with qiskit_aer 0.12.2 it works

[rrodenbusch]

@doichanj I am happy to work on this if you would like me to.

Workaround for backends derived from BackendV2

# Works for IBMProvider() backends
# Since configuration.description is set to the value of backend.description
# setting the value of backend.description avoids the exception

from qiskit.providers.backend import BackendV1, BackendV2
provider=IBMProvider()
backend=provider.get_backend("ibm_nairobi")
if isinstance(backend,BackendV2):
if hasattr(backend.configuration(),'description'): # use an existing description
backend.description = backend.configuration().description
else:
backend.description = 'My Description'

Backends derived from BackendV1

I do not see a consistent workaround for these backends. If the backend does not set and copy a description in the backend.configuration() method (e.g. any derived from ConfigurableFakeBackend), there is no workaround .
A few lines of code in the AerSimulator.from_backend would correct the exception for all backends.
Adding description = None, to the declaration for user definition
And adding an explicit check for the existence of the attribute
if description is not None or not hasattr(configuration,'description'):
configuration.description = description

[doichanj]

@rrodenbusch Thank you, I'm now fixing this issue, but it takes some time to release 0.13.1 with this fix, so it is helpful to avoid this error