Fix unresolved review comments from PR #326 Qiskit 2 support

docs/install/install.rst

@@ -10,18 +10,19 @@ sQUlearn requires a recent python3 (>=3.10) installation.
 Additionally the following python packages are necessary: ::
 
     bayesian-optimization>=1.4.3,<2,
-    dill>=0.3.4,
-    mapomatic>=0.10.0,
+    dill>=0.3.5,
+    mapomatic>=0.12.0,
     networkx>=3.0,
-    numpy>=1.20,
+    numpy>=1.21,
     pennylane>=0.34.0,
     qiskit>=1.0.0,
-    qiskit-aer>=0.13.0,
+    qiskit-aer>=0.14.0.1,
     qiskit-algorithms>=0.3.0,
-    qiskit-ibm-runtime>=0.20.0,
+    qiskit-ibm-runtime>=0.19.0,
     qiskit-machine-learning>=0.7.0,
     scipy>=1.8.0,
     scikit-learn>=1.2.0,
+    sympy>=1.8,
     tqdm>=4.1.0,
     qulacs>=0.6.0,
 

src/squlearn/util/optree/optree_evaluate.py

@@ -25,7 +25,14 @@
 )
 
 QISKIT_SMALLER_1_2 = version.parse(qiskit_version) < version.parse("1.2.0")
-QISKIT_SMALLER_2_0 = version.parse(qiskit_version) < version.parse("2.0.0")
+
+from ..executor import (
+    QISKIT_SMALLER_2_0,
+    BaseSamplerV1,
+    BaseEstimatorV1,
+    BaseSamplerV2,
+    BaseEstimatorV2,
+)
 
 if QISKIT_SMALLER_1_2:
 
@@ -40,17 +47,18 @@ class BitArray:
 else:
 
     def _pauli_expval_with_variance(counts, paulis):
-        """Dummy function for Qiskit >= 2.0."""
-        pass
-
+        """Placeholder for Qiskit >= 2.0 when using legacy V1 sampler results.
 
-from ..executor import (
-    QISKIT_SMALLER_2_0,
-    BaseSamplerV1,
-    BaseEstimatorV1,
-    BaseSamplerV2,
-    BaseEstimatorV2,
-)
+        For Qiskit 2.x, `_pauli_expval_with_variance` from `backend_estimator` is no longer
+        available in the same form. If this function is reached, it indicates that a
+        legacy (V1) sampler result is being processed with Qiskit >= 2.0, which is not
+        supported by this compatibility layer.
+        """
+        raise NotImplementedError(
+            "Support for evaluating expectation values via `_pauli_expval_with_variance` "
+            "with Qiskit >= 2.0 is not implemented. Ensure that you are not using a V1 "
+            "sampler with Qiskit 2.x, or update the code to use the V2 primitives."
+        )
 
 
 def _check_tree_for_matrix_compatibility(element: Union[OpTreeNodeBase, OpTreeLeafBase]):

src/squlearn/util/pennylane/pennylane_circuit.py

@@ -337,8 +337,17 @@ def build_circuit_instructions(self, circuit: QuantumCircuit) -> tuple:
                 pennylane_gates_wires.extend(if_else_pennylane_gates_wires)
 
             else:
-                # Add the condition None to the list of conditions
-                pennylane_conditions.append(None)
+                # Extract classical condition for non-if_else operations, if any
+                condition = None
+                if hasattr(op.operation, "condition") and op.operation.condition is not None:
+                    classical_bits = op.operation.condition[0]
+                    val = op.operation.condition[1]
+                    if isinstance(classical_bits, Clbit):
+                        bit_index = circuit.find_bit(classical_bits).index
+                    else:
+                        bit_index = [circuit.find_bit(b).index for b in classical_bits]
+                    condition = (bit_index, val)
+                pennylane_conditions.append(condition)
 
                 # Get the parameter tuple of the operation
                 param_tuple = None

tests/util/test_pennylane_circuit.py

@@ -1,9 +1,6 @@
 """Tests for PennyLaneCircuit, focusing on if_else gate handling."""
 
 import pytest
-import numpy as np
-import pennylane as qml
-import pennylane.numpy as pnp
 
 from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
 from qiskit.circuit import ParameterVector