Fix: Ensure QubitOperator is simplified before sparse conversion

src/openfermion/linalg/sparse_tools.py

@@ -13,6 +13,7 @@
 
 import itertools
 from functools import reduce
+import warnings
 import numpy.linalg
 import numpy
 
@@ -1270,6 +1271,13 @@ def get_sparse_operator(operator, n_qubits=None, trunc=None, hbar=1.0):
     elif isinstance(operator, FermionOperator):
         return jordan_wigner_sparse(operator, n_qubits)
     elif isinstance(operator, QubitOperator):
+        if hasattr(operator, "simplify"):
+            operator.simplify()
+        else:
+            warnings.warn(
+                "QubitOperator.simplify() not found. "
+                "Ensure your operator is simplified to avoid errors."
+            )
         return qubit_operator_sparse(operator, n_qubits)
     elif isinstance(operator, (BosonOperator, QuadOperator)):
         return boson_operator_sparse(operator, trunc, hbar)

src/openfermion/linalg/sparse_tools_test.py

@@ -1841,6 +1841,11 @@ def test_sparse_matrix_linearity(self):
         self.assertEqual(list(sparse2.data), [2] * 8)
         self.assertEqual(list(sparse2.indices), [0, 3, 5, 6, 9, 10, 12, 15])
 
+    def test_get_sparse_operator_simplifies_qubit_operator(self):
+        op = QubitOperator('X0') + QubitOperator('X0')
+        sparse = get_sparse_operator(op)
+        self.assertIsNotNone(sparse)
+
 
 class GetSparseOperatorFermionTest(unittest.TestCase):
     def test_sparse_matrix_zero_n_qubit(self):