remote: Allow passing of options in get_backend()

When we introduced the local provider, we made it so we declare
its options (nb_photons, kappa_1...) when using get_backend().

This is contradictory to what is happening in the remote provider,
where options must be passed in execute().

This commit harmonizes this behaviour by allowing to set the options
in get_backend() for the remote provider.
(which actually makes some sense to do it like this when we want to
set the nb_photons for example).
This allows to quickly swap between the local and remote provider.

We aim to stay as permissive as possible, by still letting the user
passing options at execute() for the remote provider.

qiskit_alice_bob_provider/remote/backend.py

@@ -67,6 +67,14 @@ def get_translation_stage_plugin(self):
         in translation_plugin.StatePreparationPlugin"""
         return self._translation_plugin
 
+    def update_options(self, option_updates: Dict[str, Any]) -> Options:
+        options: Options = self.options
+        for key, value in option_updates.items():
+            if not hasattr(options, key):
+                raise ValueError(f'Backend does not support option "{key}"')
+            options.update_options(**{key: value})
+        return options
+
     def run(self, run_input: QuantumCircuit, **kwargs) -> AliceBobRemoteJob:
         """Run the quantum circuit on the Alice & Bob backend by calling the
         Alice & Bob API.
@@ -83,11 +91,7 @@ def run(self, run_input: QuantumCircuit, **kwargs) -> AliceBobRemoteJob:
                 Wait for the results by calling
                 :func:`AliceBobRemoteJob.result`.
         """
-        options: Options = self.options
-        for key, value in kwargs.items():
-            if not hasattr(options, key):
-                raise ValueError(f'Backend does not support option "{key}"')
-            options.update_options(**{key: value})
+        options = self.update_options(kwargs)
         input_params = _ab_input_params_from_options(options)
         job = jobs.create_job(self._api_client, self.name, input_params)
         run_input = PassManager([EnsurePreparationPass()]).run(run_input)

qiskit_alice_bob_provider/remote/provider.py

@@ -52,6 +52,14 @@ def __init__(
         for ab_target in list_targets(client):
             self._backends.append(AliceBobRemoteBackend(client, ab_target))
 
+    def get_backend(self, name=None, **kwargs) -> AliceBobRemoteBackend:
+        backend = super().get_backend(name)
+        # We allow to set the options when getting the backend,
+        # to align with what we do in the local provider.
+        if kwargs:
+            backend.update_options(kwargs)
+        return backend
+
     def backends(
         self, name: Optional[str] = None, **kwargs
     ) -> List[BackendV2]:

tests/remote/test_against_real_server.py

@@ -34,7 +34,9 @@ def test_happy_path(base_url: str, api_key: str) -> None:
         api_key=api_key,
         url=base_url,
     )
-    backend = provider.get_backend('EMU:1Q:LESCANNE_2020')
-    job = execute(c, backend)
+    backend = provider.get_backend(
+        'EMU:1Q:LESCANNE_2020', average_nb_photons=6.0
+    )
+    job = execute(c, backend, shots=100)
     res = job.result()
     res.get_counts()

tests/remote/test_backend.py

@@ -28,13 +28,47 @@
 
 from qiskit_alice_bob_provider.remote.api.client import AliceBobApiException
 from qiskit_alice_bob_provider.remote.backend import (
+    AliceBobRemoteBackend,
     _ab_input_params_from_options,
     _qiskit_to_qir,
 )
 from qiskit_alice_bob_provider.remote.provider import AliceBobRemoteProvider
 
 
-def test_options_validation(mocked_targets) -> None:
+def test_get_backend(mocked_targets) -> None:
+    provider = AliceBobRemoteProvider(api_key='foo')
+    backend = provider.get_backend('EMU:1Q:LESCANNE_2020')
+    assert isinstance(backend, AliceBobRemoteBackend)
+    assert backend.options['average_nb_photons'] == 4.0  # Default value.
+
+
+def test_get_backend_with_options(mocked_targets) -> None:
+    provider = AliceBobRemoteProvider(api_key='foo')
+    backend = provider.get_backend(
+        'EMU:1Q:LESCANNE_2020', average_nb_photons=6.0
+    )
+    assert isinstance(backend, AliceBobRemoteBackend)
+    assert backend.options['average_nb_photons'] == 6.0
+
+
+def test_get_backend_options_validation(mocked_targets) -> None:
+    provider = AliceBobRemoteProvider(api_key='foo')
+    with pytest.raises(ValueError):
+        provider.get_backend('EMU:1Q:LESCANNE_2020', average_nb_photons=40)
+    with pytest.raises(ValueError):
+        provider.get_backend('EMU:1Q:LESCANNE_2020', average_nb_photons=-1)
+    with pytest.raises(ValueError):
+        provider.get_backend('EMU:1Q:LESCANNE_2020', shots=0)
+    with pytest.raises(ValueError):
+        provider.get_backend('EMU:1Q:LESCANNE_2020', shots=1e10)
+    with pytest.raises(ValueError):
+        provider.get_backend('EMU:1Q:LESCANNE_2020', bad_option=1)
+
+
+def test_execute_options_validation(mocked_targets) -> None:
+    # We are permissive in our options sytem, allowing the user to both
+    # define options when creating the backend and executing.
+    # We therefore need to test both behaviors.
     c = QuantumCircuit(1, 1)
     provider = AliceBobRemoteProvider(api_key='foo')
     backend = provider.get_backend('EMU:1Q:LESCANNE_2020')