extend fix to general PauliSumOp

qiskit/opflow/primitive_ops/pauli_sum_op.py

@@ -54,7 +54,7 @@ def __init__(
                 f"PauliSumOp can only be instantiated with SparsePauliOp, not {type(primitive)}"
             )
 
-        super().__init__(primitive, coeff=coeff)
+        super().__init__(primitive.copy(), coeff=coeff)
         self._grouping_type = grouping_type
 
     def primitive_strings(self) -> Set[str]:
@@ -210,13 +210,15 @@ def permute(self, permutation: List[int]) -> "PauliSumOp":
         if length > self.num_qubits:
             spop = self.primitive.tensor(SparsePauliOp(Pauli("I" * (length - self.num_qubits))))
         else:
-            spop = self.primitive.copy()
+            spop = self.primitive
+
+        permuted = PauliSumOp(spop, self.coeff)
 
         permutation = [i for i in range(length) if i not in permutation] + permutation
         permu_arr = np.arange(length)[np.argsort(permutation)]
-        spop.paulis.x = spop.paulis.x[:, permu_arr]
-        spop.paulis.z = spop.paulis.z[:, permu_arr]
-        return PauliSumOp(spop, self.coeff)
+        permuted.primitive.paulis.x = permuted.primitive.paulis.x[:, permu_arr]
+        permuted.primitive.paulis.z = permuted.primitive.paulis.z[:, permu_arr]
+        return permuted
 
     def compose(
         self,

releasenotes/notes/fix-pauli-sum-op-permute-a9b742f3a2fad934.yaml

@@ -1,7 +1,8 @@
 ---
 fixes:
   - |
-    Fix a bug in :meth:`qiskit.opflow.PauliSumOp.permute` where the original object on which
-    the method is called is permuted, instead of only returning a new, permuted copy. 
-    This bug only occured for permutations that left the number of qubits in the operator 
-    unchanged.
+    Fix a bug in the :class:`~qiskit.opflow.PauliSumOp` which previously stored the
+    :class:`~qiskit.quantum_info.SparsePauliOp` it was instantiated with by reference and not
+    by value. This led to several bugs, where e.g. the ``PauliSumOp`` was affected by changes in the
+    original ``SparsePauliOp`` or methods such as :meth:`~qiskit.opflow.PauliSumOp.permute` modified
+    the object they are called on instead of leaving them unchanged.

test/python/opflow/test_pauli_sum_op.py

@@ -56,6 +56,17 @@ def test_construct(self):
         self.assertEqual(pauli_sum.coeff, coeff)
         self.assertEqual(pauli_sum.num_qubits, 4)
 
+    def test_primitive_is_copied(self):
+        """Test the PauliSumOp is not affected by changes of the primitive after construction."""
+        sparse_pauli = SparsePauliOp(Pauli("X"), coeffs=[1.0])
+        pauli_sum = PauliSumOp(sparse_pauli)
+
+        # change SparsePauliOp from which PauliSumOp is constructed
+        sparse_pauli.coeffs[0] = 2
+
+        # assert PauliSumOp is unchanged
+        self.assertEqual(pauli_sum.primitive.coeffs[0], 1)
+
     def test_coeffs(self):
         """ListOp.coeffs test"""
         sum1 = SummedOp(