Bugfix: ctrl_decomp_zyz - isclose => allclose

doc/releases/changelog-dev.md

@@ -512,8 +512,11 @@
 
 <h3>Bug fixes 🐛</h3>
 
+* `ctrl_decomp_zyz` is now differentiable.
+  [(#5198)](https://github.com/PennyLaneAI/pennylane/pull/5198)
+
 * `qml.ops.Pow.matrix()` is now differentiable with TensorFlow with integer exponents.
-[(#5178)](https://github.com/PennyLaneAI/pennylane/pull/5178)
+  [(#5178)](https://github.com/PennyLaneAI/pennylane/pull/5178)
 
 * The `qml.MottonenStatePreparation` template is updated to include a global phase operation.
   [(#5166)](https://github.com/PennyLaneAI/pennylane/pull/5166)

pennylane/ops/op_math/controlled_decompositions.py

@@ -193,9 +193,9 @@ def decomp_circuit(op):
 
     decomp = []
 
-    if not qml.math.isclose(0.0, phi, atol=1e-8, rtol=0):
+    if not qml.math.allclose(0.0, phi, atol=1e-8, rtol=0):
         decomp.append(qml.RZ(phi, wires=target_wire))
-    if not qml.math.isclose(0.0, theta / 2, atol=1e-8, rtol=0):
+    if not qml.math.allclose(0.0, theta / 2, atol=1e-8, rtol=0):
         decomp.extend(
             [
                 qml.RY(theta / 2, wires=target_wire),
@@ -205,10 +205,10 @@ def decomp_circuit(op):
         )
     else:
         decomp.append(qml.ctrl(qml.PauliX(wires=target_wire), control=control_wires))
-    if not qml.math.isclose(0.0, -(phi + omega) / 2, atol=1e-6, rtol=0):
+    if not qml.math.allclose(0.0, -(phi + omega) / 2, atol=1e-6, rtol=0):
         decomp.append(qml.RZ(-(phi + omega) / 2, wires=target_wire))
     decomp.append(qml.ctrl(qml.PauliX(wires=target_wire), control=control_wires))
-    if not qml.math.isclose(0.0, (omega - phi) / 2, atol=1e-8, rtol=0):
+    if not qml.math.allclose(0.0, (omega - phi) / 2, atol=1e-8, rtol=0):
         decomp.append(qml.RZ((omega - phi) / 2, wires=target_wire))
 
     return decomp

pennylane/ops/op_math/controlled_ops.py

@@ -939,7 +939,6 @@ def compute_decomposition(wires):  # pylint: disable=arguments-differ
 
 
 def _check_and_convert_control_values(control_values, control_wires):
-
     if isinstance(control_values, str):
         # Make sure all values are either 0 or 1
         if not set(control_values).issubset({"1", "0"}):

tests/ops/op_math/test_controlled_decompositions.py

@@ -133,6 +133,41 @@ def expected_circuit():
 
         assert np.allclose(res, expected, atol=tol, rtol=0)
 
+    @pytest.mark.parametrize("control_wires", ([1], [1, 2], [1, 2, 3]))
+    def test_decomposition_circuit_gradient(self, control_wires, tol):
+        """Tests that the controlled decomposition of a single-qubit operation
+        behaves as expected in a quantum circuit"""
+        n_qubits = 4
+        np.random.seed(1337)
+
+        dev = qml.device("default.qubit", wires=n_qubits)
+        init_state = np.random.rand(2**n_qubits) + 1.0j * np.random.rand(2**n_qubits)
+        init_state /= np.sqrt(np.dot(np.conj(init_state), init_state))
+        init_state = np.array(init_state)
+        target_wires = [0]
+        control_values = [True] * len(control_wires)
+
+        def circuit(p):
+            qml.StatePrep(init_state, wires=range(n_qubits))
+            qml.ctrl(
+                qml.Rot(*p, wires=target_wires),
+                control_wires,
+                control_values=control_values,
+            )
+            return qml.probs(wires=target_wires)
+
+        circ_ad = qml.QNode(circuit, dev, diff_method="adjoint")
+        circ_bp = qml.QNode(circuit, dev, diff_method="backprop")
+        par = qml.numpy.array([0.1234, 0.235, 0.5678])
+        jac_ad = qml.jacobian(circ_ad)(par)
+        jac_bp = qml.jacobian(circ_bp)(par)
+
+        # different methods must agree
+        assert jac_ad.size == 2 * 3
+        assert np.allclose(jac_ad.shape, [2, 3])
+        assert np.allclose(jac_ad.shape, jac_bp.shape)
+        assert np.allclose(jac_ad, jac_bp, atol=tol, rtol=0)
+
     @pytest.mark.parametrize("op", su2_ops)
     @pytest.mark.parametrize("control_wires", ([1], [1, 2], [1, 2, 3]))
     def test_decomposition_matrix(self, op, control_wires, tol):