Add tensor unwrapping in BaseQNode for keyword arguments

.github/CHANGELOG.md

@@ -208,6 +208,11 @@
 
 <h3>Bug fixes</h3>
 
+* PennyLane tensor objects are now unwrapped in BaseQNode when passed as a
+  keyword argument to the quantum function.
+  [(#903)](https://github.com/PennyLaneAI/pennylane/pull/903)
+  [(#893)](https://github.com/PennyLaneAI/pennylane/pull/893)
+
 * The new tape mode now prevents multiple observables from being evaluated on the same wire
   if the observables are not qubit-wise commuting Pauli words.
   [(#882)](https://github.com/PennyLaneAI/pennylane/pull/882)
@@ -229,7 +234,7 @@
 This release contains contributions from (in alphabetical order):
 
 Thomas Bromley, Christina Lee, Olivia Di Matteo, Anthony Hayes, Josh Izaac, Nathan Killoran,
-Romain Moyard, Maria Schuld
+Romain Moyard, Maria Schuld, Antal Száva
 
 
 # Release 0.12.0 (current release)

pennylane/qnodes/base.py

@@ -453,6 +453,8 @@ def qfunc(a, w):
                 Each positional argument is replaced with a :class:`~.variable.Variable` instance.
             kwargs (dict[str, Any]): Auxiliary arguments passed to the quantum function.
         """
+        kwargs = self.unwrap_tensor_kwargs(kwargs)
+
         # Get the name of the qfunc's arguments
         full_argspec = inspect.getfullargspec(self.func)
 
@@ -525,6 +527,25 @@ def qfunc(a, w):
 
         return arg_vars, kwarg_vars
 
+    @staticmethod
+    def unwrap_tensor_kwargs(kwargs):
+        """Unwraps the pennylane.numpy.tensor objects that were passed as
+        keyword arguments so that they can be handled as gate parameters by
+        arbitrary devices.
+
+        Args:
+            kwargs (dict[str, Any]): Auxiliary arguments passed to the quantum function.
+
+        Returns:
+            dict[str, Any]: Auxiliary arguments passed to the quantum function
+            in an unwrapped form (if applicable).
+        """
+        for k, v in kwargs.items():
+            if isinstance(v, qml.numpy.tensor):
+                kwargs[k] = v.unwrap()
+
+        return kwargs
+
     def _construct(self, args, kwargs):
         """Construct the quantum circuit graph by calling the quantum function.
 

pennylane/templates/layers/random.py

@@ -25,7 +25,6 @@
     get_shape,
 )
 from pennylane.wires import Wires
-from pennylane.numpy import tensor
 
 
 def random_layer(weights, wires, ratio_imprim, imprimitive, rotations, seed):
@@ -51,10 +50,7 @@ def random_layer(weights, wires, ratio_imprim, imprimitive, rotations, seed):
             gate = np.random.choice(rotations)
             rnd_wire = wires.select_random(1)
 
-            if isinstance(weights[i], tensor):
-                gate(weights[i].unwrap(), wires=rnd_wire)
-            else:
-                gate(weights[i], wires=rnd_wire)
+            gate(weights[i], wires=rnd_wire)
 
             i += 1
         else:

tests/templates/test_subroutines.py

@@ -913,7 +913,7 @@ def test_uccsd_operations(self, s_wires, d_wires, weights, ref_gates):
                 [[0, 1, 2]],
                 [],
                 np.array([1.2, 1, 0, 0]),
-                "BasisState parameter must consist of 0 or 1 integers",
+                "Elements of 'init_state' must be integers",
             ),
             (
                 np.array([-2.8]),

tests/test_numpy_wrapper.py

@@ -497,3 +497,62 @@ def test_convert_array(self):
         assert np.all(res == data)
         assert isinstance(res, np.ndarray)
         assert not isinstance(res, np.tensor)
+
+    def test_single_gate_parameter(self, monkeypatch):
+        """Test that when supplied a PennyLane tensor, a QNode passes an
+        unwrapped tensor as the argument to a gate taking a single parameter"""
+        dev = qml.device("default.qubit", wires=4)
+
+        @qml.qnode(dev)
+        def circuit(phi=None):
+            for y in phi:
+                for idx, x in enumerate(y):
+                    qml.RX(x, wires=idx)
+            return qml.expval(qml.PauliZ(0))
+
+        phi = np.tensor([[0.04439891, 0.14490549, 3.29725643, 2.51240058]])
+
+        with qml._queuing.OperationRecorder() as rec:
+            circuit(phi=phi)
+
+        for i in range(phi.shape[1]):
+            # Test each rotation applied
+            assert rec.queue[0].name == "RX"
+            assert len(rec.queue[0].parameters) == 1
+
+            # Test that the gate parameter is not a PennyLane tensor, but a
+            # float
+            assert not isinstance(rec.queue[0].parameters[0], np.tensor)
+            assert isinstance(rec.queue[0].parameters[0], float)
+
+    def test_multiple_gate_parameter(self):
+        """Test that when supplied a PennyLane tensor, a QNode passes arguments
+        as unwrapped tensors to a gate taking multiple parameters"""
+        dev = qml.device("default.qubit", wires=1)
+
+        @qml.qnode(dev)
+        def circuit(phi=None):
+            for idx, x in enumerate(phi):
+                qml.Rot(*x, wires=idx)
+            return qml.expval(qml.PauliZ(0))
+
+        phi = np.tensor([[0.04439891, 0.14490549, 3.29725643]])
+
+
+        with qml._queuing.OperationRecorder() as rec:
+            circuit(phi=phi)
+
+        # Test the rotation applied
+        assert rec.queue[0].name == "Rot"
+        assert len(rec.queue[0].parameters) == 3
+
+        # Test that the gate parameters are not PennyLane tensors, but a
+        # floats
+        assert not isinstance(rec.queue[0].parameters[0], np.tensor)
+        assert isinstance(rec.queue[0].parameters[0], float)
+
+        assert not isinstance(rec.queue[0].parameters[1], np.tensor)
+        assert isinstance(rec.queue[0].parameters[1], float)
+
+        assert not isinstance(rec.queue[0].parameters[2], np.tensor)
+        assert isinstance(rec.queue[0].parameters[2], float)