[WIP][Bug Fix] Fixing the pow method on qml.TShift

doc/releases/changelog-dev.md

@@ -321,6 +321,9 @@
   [(#6278)](https://github.com/PennyLaneAI/pennylane/pull/6278)
   [(#6310)](https://github.com/PennyLaneAI/pennylane/pull/6310)
 
+* Fixes a bug preventing `qml.TAdd`, `qml.TClock`, and `qml.TShift` from being raised to the power of 2.
+  [(#6356)](https://github.com/PennyLaneAI/pennylane/pull/6356)
+
 * Fixes a test after updating to the nightly version of Catalyst.
   [(#6362)](https://github.com/PennyLaneAI/pennylane/pull/6362)
 

pennylane/operation.py

@@ -1478,16 +1478,15 @@ def pow(self, z: float) -> list["Operator"]:
             list[:class:`~.operation.Operator`]
 
         """
-        # Child methods may call super().pow(z%period) where op**period = I
-        # For example, PauliX**2 = I, SX**4 = I
-        # Hence we define 0 and 1 special cases here.
-        if z == 0:
-            return []
-        if z == 1:
-            if QueuingManager.recording():
-                return [qml.apply(self)]
-            return [copy.copy(self)]
-        raise PowUndefinedError
+        if not isinstance(z, int):
+            raise PowUndefinedError
+
+        if z < 0:
+            raise PowUndefinedError
+
+        if QueuingManager.recording():
+            return [qml.apply(self) for _ in range(z)]
+        return [copy.copy(self) for _ in range(z)]
 
     def queue(self, context: QueuingManager = QueuingManager):
         """Append the operator to the Operator queue."""

tests/ops/qutrit/test_qutrit_non_parametric_ops.py

@@ -138,12 +138,17 @@ def test_period_three_ops_pow_offset_1(self, op, offset):
     @pytest.mark.parametrize("op", period_three_ops)
     @pytest.mark.parametrize("offset", (0, 3))
     def test_period_three_ops_pow_offset_2(self, op, offset):
-        """Tests that ops with a period ==3 raise a PowUndefinedError when raised
+        """Tests that ops with a period ==3 two queued copies of themselves when
         to a power that is 2+multiple of three."""
 
         # When raising to power == 2 mod 3
-        with pytest.raises(qml.operation.PowUndefinedError):
-            op.pow(2 + offset)
+        with qml.queuing.AnnotatedQueue() as q:
+            op_list = op.pow(2 + offset)
+
+        assert q.queue[0] is op_list[0]
+        assert q.queue[1] is op_list[1]
+        qml.assert_equal(op_list[0], op)
+        qml.assert_equal(op_list[1], op)
 
     @pytest.mark.parametrize("op", period_three_ops + period_two_ops)
     def test_period_two_three_noninteger_power(self, op):
@@ -168,7 +173,7 @@ def test_no_pow_ops(self, op):
         assert len(op_pow) == 1
         assert op_pow[0].__class__ == op.__class__
 
-        pows = [0.1, 2, -2, -2.5]
+        pows = [0.1, -2.5]
 
         for pow in pows:
             with pytest.raises(qml.operation.PowUndefinedError):