Fix PVQD loss function

qiskit/algorithms/time_evolvers/pvqd/pvqd.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2019, 2022.
+# (C) Copyright IBM 2019, 2022, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -270,7 +270,7 @@ def evaluate_loss(displacement: np.ndarray | list[np.ndarray]) -> float | list[f
             # the first state does not have free parameters so values_1 will be None by default
             try:
                 job = self.fidelity_primitive.run(states1, states2, values_2=param_dicts2)
-                fidelities = job.result().fidelities
+                fidelities = np.array(job.result().fidelities)
             except Exception as exc:
                 raise AlgorithmError("The primitive job failed!") from exc
 
@@ -279,7 +279,7 @@ def evaluate_loss(displacement: np.ndarray | list[np.ndarray]) -> float | list[f
 
             # in principle, we could add different loss functions here, but we're currently
             # not aware of a use-case for a different one than in the paper
-            return 1 - np.abs(fidelities) ** 2
+            return 1 - fidelities
 
         if _is_gradient_supported(ansatz) and self.use_parameter_shift:
 

releasenotes/notes/fix-pvqd-loss-cb1ebe0258f225de.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fixed loss function in PVQD. Removed extra abs**2 that is already covered by the fidelity primitive