[WIP] Fix TrotterProduct differentiability with parameter-shift bug

doc/releases/changelog-dev.md

@@ -320,6 +320,9 @@
 
 <h3>Bug fixes 🐛</h3>
 
+* Fixes incorrect differentiation of `TrotterProduct` when using `diff_method="parameter-shift"`.
+  [(#6432)](https://github.com/PennyLaneAI/pennylane/pull/6432)
+
 * Patches the `math` module to function with autoray 0.7.0.
   [(#6429)](https://github.com/PennyLaneAI/pennylane/pull/6429)
 

pennylane/ops/op_math/exp.py

@@ -164,6 +164,7 @@ class Exp(ScalarSymbolicOp, Operation):
 
     """
 
+    grad_method = None
     control_wires = Wires([])
     _name = "Exp"
 

pennylane/templates/subroutines/trotter.py

@@ -186,6 +186,8 @@ def my_circ(c1, c2, time):
         (tensor(0.00961064, requires_grad=True), tensor(-0.12338274, requires_grad=True), tensor(-5.43401259, requires_grad=True))
     """
 
+    grad_method = None
+
     @classmethod
     def _primitive_bind_call(cls, *args, **kwargs):
         # accepts no wires, so bypasses the wire processing.

tests/ops/functions/conftest.py

@@ -57,7 +57,7 @@
     (qml.s_prod(1.1, qml.RX(1.1, 0)), {}),
     (qml.prod(qml.PauliX(0), qml.PauliY(1), qml.PauliZ(0)), {}),
     (qml.ctrl(qml.RX(1.1, 0), 1), {}),
-    (qml.exp(qml.PauliX(0), 1.1), {}),
+    (qml.exp(qml.PauliX(0), 1.1), {"skip_differentiation": True}),
     (qml.pow(qml.IsingXX(1.1, [0, 1]), 2.5), {}),
     (qml.ops.Evolution(qml.PauliX(0), 5.2), {}),
     (qml.QutritBasisState([1, 2, 0], wires=[0, 1, 2]), {"skip_differentiation": True}),

tests/templates/test_subroutines/test_trotter.py

@@ -447,7 +447,6 @@ def test_copy(self, hamiltonian, time, n, order):
         assert op.hyperparameters == new_op.hyperparameters
         assert op is not new_op
 
-    @pytest.mark.xfail(reason="https://github.com/PennyLaneAI/pennylane/issues/6333", strict=False)
     @pytest.mark.parametrize("hamiltonian", test_hamiltonians)
     def test_standard_validity(self, hamiltonian):
         """Test standard validity criteria using assert_valid."""