fixed expval

Author: Dpbm

aer_plugin/backends/aer.py

@@ -17,20 +17,21 @@ def __init__(
     def _exec_expval(self, circuit: QuantumCircuit) -> Results:
         """Extracts expval using EstimatorV2"""
 
-        obs = self._metadata.get("obs")
+        obs_list = self._metadata.get("obs")
         assert (
-            obs is not None and len(obs) > 0
+            obs_list is not None and len(obs_list) > 0 and isinstance(obs_list, list)
         ), "You need to provide the observables to get the expectation value!"
 
         # pylint: disable=import-outside-toplevel
         from qiskit_aer.primitives import EstimatorV2
         from qiskit.quantum_info import SparsePauliOp
 
         estimator = EstimatorV2()
-        result = estimator.run([(circuit, SparsePauliOp.from_list(obs))]).result()
+        results = estimator.run(
+            [(circuit, SparsePauliOp.from_list(obs)) for obs in obs_list]
+        ).result()
 
-        # to ensure the expval result will be a flot (for mypy)
-        return result[0].data.evs  # type: ignore
+        return [result.data.evs for result in results]  # type: ignore
 
     def _exec_counts(self, circuit: QuantumCircuit) -> Results:
         """Extracts counts using AerSimulator directly"""

aer_plugin/interface.py

@@ -12,7 +12,7 @@
 Metadata = Dict[Any, Any]
 ResultType = str
 QasmFilePath = str
-Results = Dict[str | int, float] | float
+Results = Dict[str | int, float] | List[float]
 
 
 def check_backend(func):

tests/test_run.py

@@ -68,21 +68,32 @@ def test_incorrect_quasi_dist(self):
     def test_correct_expval_one_obs(self):
         """should raise no error and evaluate the observable ZZ to 1"""
         result = Plugin().execute(
-            "aer", "./tests/valid_expval.qasm", {"obs": [("ZZ", 1)]}, "expval"
+            "aer", "./tests/valid_expval.qasm", {"obs": [[("ZZ", 1)]]}, "expval"
         )
 
-        assert result == 1.0
+        assert result == [1.0]
 
-    def test_correct_expval_two_obs(self):
+    def test_correct_expval_two_obs_same_pub(self):
         """should raise no error and sum up all expectation values (total=3)"""
         result = Plugin().execute(
             "aer",
             "./tests/valid_expval.qasm",
-            {"obs": [("ZI", 1), ("IZ", 1), ("ZZ", 1)]},
+            {"obs": [[("ZI", 1), ("IZ", 1), ("ZZ", 1)]]},
             "expval",
         )
 
-        assert result == 3.0
+        assert result == [3.0]
+
+    def test_correct_expval_one_obs_per_pub(self):
+        """should return a list of expectation values with size 2"""
+        result = Plugin().execute(
+            "aer",
+            "./tests/valid_expval.qasm",
+            {"obs": [[("ZI", 1)], [("ZI", 1)]]},
+            "expval",
+        )
+
+        assert result == [1.0, 1.0]
 
     def test_incorrect_expval_no_obs(self):
         """should raise an error, once there's no observables defined."""
@@ -94,6 +105,6 @@ def test_incorrect_expval_circuit_with_measurements(self):
         """should raise no error, once the circuit has measurements but we can evaluate the expval as well."""
 
         result = Plugin().execute(
-            "aer", "./tests/expval_measurements.qasm", {"obs": [("II", 1)]}, "expval"
+            "aer", "./tests/expval_measurements.qasm", {"obs": [[("II", 1)]]}, "expval"
         )
-        assert result == 1.0
+        assert result == [1.0]