Fix of eval_observables() when quantum_circuit is a StateFn.

qiskit/algorithms/aux_ops_evaluator.py

@@ -122,8 +122,10 @@ def _prepare_list_op(
     if isinstance(observables, dict):
         observables = list(observables.values())
 
-    state = StateFn(quantum_state)
-    return ListOp([StateFn(obs, is_measurement=True).compose(state) for obs in observables])
+    if not isinstance(quantum_state, StateFn):
+        quantum_state = StateFn(quantum_state)
+
+    return ListOp([StateFn(obs, is_measurement=True).compose(quantum_state) for obs in observables])
 
 
 def _prepare_result(

releasenotes/notes/fix-aux-ops-evaluator-83ce1606d1ad19b3.yaml

@@ -0,0 +1,6 @@
+fixes:
+  - |
+    The :func:`~qiskit.algorithms.eval_observables` function raised an error when the 
+    ``quantum_state`` argument is a :class:`~qiskit.opflow.StateFn`. 
+    This error was fixed and ``eval_observables`` now correctly supports all input types
+    specifying in the type hints.

test/python/algorithms/test_aux_ops_evaluator.py

@@ -24,7 +24,16 @@
 from qiskit.algorithms import eval_observables
 from qiskit import BasicAer, QuantumCircuit
 from qiskit.circuit.library import EfficientSU2
-from qiskit.opflow import PauliSumOp, X, Z, I, ExpectationFactory, OperatorBase, ExpectationBase
+from qiskit.opflow import (
+    PauliSumOp,
+    X,
+    Z,
+    I,
+    ExpectationFactory,
+    OperatorBase,
+    ExpectationBase,
+    StateFn,
+)
 from qiskit.utils import QuantumInstance, algorithm_globals
 
 
@@ -155,6 +164,17 @@ def test_eval_observables(self, observables: ListOrDict[OperatorBase]):
                         quantum_instance,
                     )
 
+                with self.subTest(msg="Test StateFn."):
+                    statefn = StateFn(bound_ansatz)
+                    self._run_test(
+                        expected_result,
+                        statefn,
+                        decimal,
+                        expectation,
+                        observables,
+                        quantum_instance,
+                    )
+
 
 if __name__ == "__main__":
     unittest.main()