Fix wires object handling in Sum.terms method

doc/releases/changelog-dev.md

@@ -616,6 +616,9 @@ same information.
 
 <h3>Bug fixes 🐛</h3>
 
+* `Identity` operator wires are properly tracked when using `qml.Sum.terms`.
+  [(#6750)](https://github.com/PennyLaneAI/pennylane/pull/6750)
+
 * `qml.ControlledQubitUnitary` has consistent behaviour with program capture enabled. 
   [(#6719)](https://github.com/PennyLaneAI/pennylane/pull/6719)
 

pennylane/ops/op_math/sum.py

@@ -465,7 +465,7 @@ def terms(self):
         # try using pauli_rep:
         if pr := self.pauli_rep:
             with qml.QueuingManager.stop_recording():
-                ops = [pauli.operation() for pauli in pr.keys()]
+                ops = [pauli.operation(self.wires) for pauli in pr.keys()]
             return list(pr.values()), ops
 
         with qml.QueuingManager.stop_recording():

tests/ops/op_math/test_sum.py

@@ -300,6 +300,17 @@ def test_terms_does_not_change_queue(self, op, coeffs_true, ops_true):
 
         assert q.queue == [op]
 
+    def test_identity_wires_are_preserved(self):
+        """Test that Identity wires are preserved after calling Sum.terms method."""
+        hamiltonian = qml.dot([1, 0.5], [qml.Identity(wires=[0, 1]), qml.PauliZ(0)])
+        coeffs, operators = hamiltonian.terms()
+        assert coeffs == [1, 0.5]
+        op1, op2 = operators
+        assert op1.name == "Identity"
+        assert op2.name == "PauliZ"
+        assert op1.wires == Wires([0, 1])
+        assert op2.wires == Wires([0])
+
     def test_eigen_caching(self):
         """Test that the eigendecomposition is stored in cache."""
         diag_sum_op = Sum(qml.PauliZ(wires=0), qml.Identity(wires=1))

tests/qchem/test_factorization.py

@@ -314,14 +314,14 @@ def test_empty_error(two_tensor):
             [  # computed manually
                 [
                     qml.PauliZ(wires=[0]),
-                    qml.Identity(wires=[0]),
+                    qml.Identity(wires=[0, 1, 2, 3]),
                     qml.PauliZ(wires=[1]),
                     qml.PauliZ(wires=[2]),
                     qml.PauliZ(wires=[3]),
                 ],
                 [
                     qml.PauliZ(wires=[0]),
-                    qml.Identity(wires=[0]),
+                    qml.Identity(wires=[0, 1, 2, 3]),
                     qml.PauliZ(wires=[1]),
                     qml.PauliZ(wires=[0]) @ qml.PauliZ(wires=[1]),
                     qml.PauliZ(wires=[2]),
@@ -338,12 +338,12 @@ def test_empty_error(two_tensor):
                     qml.PauliZ(wires=[0]) @ qml.PauliZ(wires=[3]),
                     qml.PauliZ(wires=[1]) @ qml.PauliZ(wires=[2]),
                     qml.PauliZ(wires=[1]) @ qml.PauliZ(wires=[3]),
-                    qml.Identity(wires=[2]),
+                    qml.Identity(wires=[0, 1, 2, 3]),
                     qml.PauliZ(wires=[2]) @ qml.PauliZ(wires=[3]),
                 ],
                 [
                     qml.PauliZ(wires=[0]),
-                    qml.Identity(wires=[0]),
+                    qml.Identity(wires=[0, 1, 2, 3]),
                     qml.PauliZ(wires=[1]),
                     qml.PauliZ(wires=[0]) @ qml.PauliZ(wires=[1]),
                     qml.PauliZ(wires=[2]),
@@ -392,12 +392,12 @@ def test_empty_error(two_tensor):
         ),
     ],
 )
+# pylint: disable = too-many-positional-arguments
 def test_basis_rotation_output(
     one_matrix, two_tensor, tol_factor, coeffs_ref, ops_ref, eigvecs_ref
 ):
     r"""Test that basis_rotation function returns the correct values."""
     coeffs, ops, eigvecs = qml.qchem.basis_rotation(one_matrix, two_tensor, tol_factor)
-
     for i, coeff in enumerate(coeffs):
         assert np.allclose(np.sort(coeff), np.sort(coeffs_ref[i]))