Fix the inverse method of PauliEvolutionGate

qiskit/circuit/library/pauli_evolution.py

@@ -104,9 +104,6 @@ def _define(self):
         """Unroll, where the default synthesis is matrix based."""
         self.definition = self.synthesis.synthesize(self)
 
-    def inverse(self) -> "PauliEvolutionGate":
-        return PauliEvolutionGate(operator=self.operator, time=-self.time, synthesis=self.synthesis)
-
     def validate_parameter(
         self, parameter: Union[int, float, ParameterExpression]
     ) -> Union[float, ParameterExpression]:

releasenotes/notes/fix-paulievo-inverse-b53a6ecd0ff9a313.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fix :meth:`~qiskit.circuit.library.PauliEvolutionGate.inverse` which previously computed the
+    inverse by inverting the evolution time, which is only the correct inverse if the operator
+    was involved correctly. In particular, this led to the inverse of Trotterization-based time
+    evolutions being incorrect.

test/python/circuit/library/test_evolution_gate.py

@@ -261,3 +261,14 @@ def test_paulisumop_coefficients_respected(self):
             circuit.data[2][0].params[0],  # Z
         ]
         self.assertListEqual(rz_angles, [20, 30, -10])
+
+    @data(LieTrotter, MatrixExponential)
+    def test_inverse(self, synth_cls):
+        """Test calculating the inverse is correct."""
+        evo = PauliEvolutionGate(X + Y, time=0.12, synthesis=synth_cls())
+
+        circuit = QuantumCircuit(1)
+        circuit.append(evo, circuit.qubits)
+        circuit.append(evo.inverse(), circuit.qubits)
+
+        self.assertTrue(Operator(circuit).equiv(np.identity(2 ** circuit.num_qubits)))