Remove input arg control wires of MultiControlledX

doc/development/deprecations.rst

@@ -73,6 +73,11 @@ for details on how to port your legacy code to the new system. The following fun
 Completed deprecation cycles
 ----------------------------
 
+* The input argument ``control_wires`` of ``MultiControlledX`` has been removed.
+
+  - Deprecated in v0.22
+  - Removed in v0.41
+
 * The ``QNode.get_best_method`` and ``QNode.best_method_str`` methods have been removed. 
   Instead, use the ``qml.workflow.get_best_diff_method`` function. 
 

doc/releases/changelog-dev.md

@@ -17,6 +17,9 @@
 
 <h3>Breaking changes 💔</h3>
 
+* The input argument `control_wires` of `MultiControlledX` has been removed.
+  [(#6832)](https://github.com/PennyLaneAI/pennylane/pull/6832)
+
 * The ``QNode.get_best_method`` and ``QNode.best_method_str`` methods have been removed. 
   Instead, use the ``qml.workflow.get_best_diff_method`` function. 
   [(#6823)](https://github.com/PennyLaneAI/pennylane/pull/6823)

pennylane/ops/op_math/controlled_ops.py

@@ -1157,12 +1157,10 @@ def _primitive_bind_call(cls, wires, control_values=None, work_wires=None, id=No
     # pylint: disable=too-many-arguments
     def __init__(
         self,
-        control_wires: WiresLike = (),
         wires: WiresLike = (),
         control_values=None,
         work_wires: WiresLike = (),
     ):
-        control_wires = Wires(() if control_wires is None else control_wires)
         wires = Wires(() if wires is None else wires)
         work_wires = Wires(() if work_wires is None else work_wires)
 
@@ -1173,27 +1171,17 @@ def __init__(
                 "supported in future releases, Use a list of booleans or integers instead.",
                 qml.PennyLaneDeprecationWarning,
             )
-        if len(control_wires) > 0:
-            warnings.warn(
-                "The control_wires keyword for MultiControlledX is deprecated, and will "
-                "be removed soon. Use wires = (*control_wires, target_wire) instead.",
-                UserWarning,
-            )
 
         if len(wires) == 0:
             raise ValueError("Must specify the wires where the operation acts on")
 
-        if len(control_wires) > 0:
-            if len(wires) != 1:
-                raise ValueError("MultiControlledX accepts a single target wire.")
-        else:
-            if len(wires) < 2:
-                raise ValueError(
-                    f"MultiControlledX: wrong number of wires. {len(wires)} wire(s) given. "
-                    f"Need at least 2."
-                )
-            control_wires = wires[:-1]
-            wires = wires[-1:]
+        if len(wires) < 2:
+            raise ValueError(
+                f"MultiControlledX: wrong number of wires. {len(wires)} wire(s) given. "
+                f"Need at least 2."
+            )
+        control_wires = wires[:-1]
+        wires = wires[-1:]
 
         control_values = _check_and_convert_control_values(control_values, control_wires)
 

tests/ops/qubit/test_non_parametric_ops.py

@@ -631,33 +631,6 @@ def test_invalid_arguments_to_init(self, wires, control_values, error_message):
         with pytest.raises(ValueError, match=error_message):
             _ = qml.MultiControlledX(wires=wires, control_values=control_values)
 
-    @pytest.mark.parametrize(
-        "control_wires, wires, control_values, error_message",
-        [
-            (
-                [0, 1],
-                [2],
-                [0, 1, 0],
-                "Length of control values must equal number of control wires.",
-            ),
-            ([0], None, [1], "Must specify the wires where the operation acts on"),
-            ([0, 1], 2, [0, 1, 1], "Length of control values must equal number of control wires."),
-            ([0, 1], [2, 3], [1, 0], "MultiControlledX accepts a single target wire."),
-        ],
-    )
-    def test_invalid_arguments_to_init_old(
-        self, control_wires, wires, control_values, error_message
-    ):
-        """Tests initializing a MultiControlledX with invalid arguments with the old interface"""
-        with pytest.warns(
-            UserWarning,
-            match="The control_wires keyword for MultiControlledX is deprecated",
-        ):
-            with pytest.raises(ValueError, match=error_message):
-                _ = qml.MultiControlledX(
-                    control_wires=control_wires, wires=wires, control_values=control_values
-                )
-
     @pytest.mark.parametrize(
         "wires, control_values, error_message",
         [
@@ -678,69 +651,6 @@ def test_invalid_str_control_values(self, wires, control_values, error_message):
             with pytest.raises(ValueError, match=error_message):
                 _ = qml.MultiControlledX(wires=wires, control_values=control_values)
 
-    @pytest.mark.parametrize(
-        "control_wires,wires,control_values",
-        [
-            ([0], 1, [0]),
-            ([0, 1], 2, [0, 0]),
-            ([0, 1], 2, [1, 0]),
-            ([1, 0], 2, [1, 0]),
-            ([0, 1], 2, [1, 1]),
-            ([0, 2], 1, [1, 0]),
-            ([1, 2, 0], 3, [1, 0, 0]),
-            ([1, 0, 2, 4], 3, [1, 0, 0, 1]),
-            ([0, 1, 2, 5, 3, 6], 4, [1, 0, 0, 0, 0, 1]),
-        ],
-    )
-    def test_mixed_polarity_controls_old(self, control_wires, wires, control_values):
-        """Test if MultiControlledX properly applies mixed-polarity
-        control values with old version of the arguments."""
-
-        target_wires = Wires(wires)
-        dev = qml.device("default.qubit", wires=len(control_wires + target_wires))
-
-        # Pick random starting state for the control and target qubits
-        control_state_weights = np.random.normal(size=2 ** (len(control_wires) + 1) - 2)
-        target_state_weights = np.random.normal(size=2 ** (len(target_wires) + 1) - 2)
-
-        @qml.qnode(dev)
-        def circuit_mpmct():
-            qml.templates.ArbitraryStatePreparation(control_state_weights, wires=control_wires)
-            qml.templates.ArbitraryStatePreparation(target_state_weights, wires=target_wires)
-
-            qml.MultiControlledX(
-                control_wires=control_wires, wires=target_wires, control_values=control_values
-            )
-            return qml.state()
-
-        # The result of applying the mixed-polarity gate should be the same as
-        # if we conjugated the specified control wires with Pauli X and applied the
-        # "regular" ControlledQubitUnitary in between.
-
-        x_locations = [x for x in range(len(control_values)) if control_values[x] == 0]
-
-        @qml.qnode(dev)
-        def circuit_pauli_x():
-            qml.templates.ArbitraryStatePreparation(control_state_weights, wires=control_wires)
-            qml.templates.ArbitraryStatePreparation(target_state_weights, wires=target_wires)
-
-            for wire in x_locations:
-                qml.PauliX(wires=control_wires[wire])
-
-            qml.ControlledQubitUnitary(X, control_wires=control_wires, wires=target_wires)
-
-            for wire in x_locations:
-                qml.PauliX(wires=control_wires[wire])
-
-            return qml.state()
-
-        with pytest.warns(UserWarning, match="deprecated"):
-            mpmct_state = circuit_mpmct()
-
-        pauli_x_state = circuit_pauli_x()
-
-        assert qml.math.allclose(mpmct_state, pauli_x_state)
-
     def test_decomposition_not_enough_wires(self):
         """Test that the decomposition raises an error if the number of wires is lower than two"""
         with pytest.raises(ValueError, match="Wrong number of wires"):