Fix stopping condition thresholds

.github/CHANGELOG.md

@@ -46,6 +46,9 @@
 
 ### Bug fixes
 
+* Ensure the stopping condition decompositions are respected for larger templated QFT and Grover operators.
+  [(#609)](https://github.com/PennyLaneAI/pennylane-lightning/pull/609)
+
 * Move concurrency group specifications from reusable Docker build workflow to the root workflows.
   [(#604)](https://github.com/PennyLaneAI/pennylane-lightning/pull/604)
 

pennylane_lightning/core/lightning_base.py

@@ -93,13 +93,13 @@ def stopping_condition(self):
         and observable) and returns ``True`` if supported by the device."""
 
         def accepts_obj(obj):
-            if obj.name == "QFT" and len(obj.wires) < 10:
-                return True
-            if obj.name == "GroverOperator" and len(obj.wires) < 13:
-                return True
-            return (not isinstance(obj, qml.tape.QuantumTape)) and getattr(
-                self, "supports_operation", lambda name: False
-            )(obj.name)
+            if obj.name == "QFT":
+                return len(obj.wires) < 10
+            if obj.name == "GroverOperator":
+                return len(obj.wires) < 13
+            is_not_tape = not isinstance(obj, qml.tape.QuantumTape)
+            is_supported = getattr(self, "supports_operation", lambda name: False)(obj.name)
+            return is_not_tape and is_supported
 
         return qml.BooleanFn(accepts_obj)
 

tests/test_decomposition.py

@@ -31,12 +31,14 @@ class TestDenseMatrixDecompositionThreshold:
     input = [
         (qml.QFT, 8, True),
         (qml.QFT, 10, False),
+        (qml.QFT, 14, False),
         (qml.GroverOperator, 8, True),
         (qml.GroverOperator, 13, False),
     ]
 
     @pytest.mark.parametrize("op, n_wires, condition", input)
     def test_threshold(self, op, n_wires, condition):
-        wires = np.linspace(0, n_wires - 1, n_wires, dtype=int)
+        wires = range(n_wires)
         op = op(wires=wires)
-        assert ld.stopping_condition.__get__(op)(op) == condition
+        dev = ld(n_wires)
+        assert dev.stopping_condition(op) == condition