V0.14.1 bump (#1083)

* PR 1082

* PR 1072

* Update vqe.py (#1077)

update `genearate_hamiltonian` refs

* PR 1074

* Add jax skip (#1066)

Co-authored-by: Josh Izaac <josh146@gmail.com>

* update changelog

* update version number

* Apply suggestions from code review

Co-authored-by: Tom Bromley <49409390+trbromley@users.noreply.github.com>
Co-authored-by: antalszava <antalszava@gmail.com>

Co-authored-by: antalszava <antalszava@gmail.com>
Co-authored-by: Tom Bromley <49409390+trbromley@users.noreply.github.com>

.github/CHANGELOG.md

@@ -1,4 +1,42 @@
-# Release 0.14.0 (current release)
+# Release 0.14.1 (current release)
+
+<h3>Bug fixes</h3>
+
+* Fixes a bug where inverse operations could not be differentiated
+  using backpropagation on `default.qubit`.
+  [(#1072)](https://github.com/PennyLaneAI/pennylane/pull/1072)
+
+* The QNode has a new keyword argument, `max_expansion`, that determines the maximum number of times
+  the internal circuit should be expanded when executed on a device. In addition, the default number
+  of max expansions has been increased from 2 to 10, allowing devices that require more than two
+  operator decompositions to be supported.
+  [(#1074)](https://github.com/PennyLaneAI/pennylane/pull/1074)
+
+* Fixes a bug where `Hamiltonian` objects created with non-list arguments
+  raised an error for arithmetic operations.
+  [(#1082)](https://github.com/PennyLaneAI/pennylane/pull/1082)
+
+* Fixes a bug where `Hamiltonian` objects with no coefficients or operations
+  would return a faulty result when used with `ExpvalCost`.
+  [(#1082)](https://github.com/PennyLaneAI/pennylane/pull/1082)
+
+* Fixes a testing bug where tests that required JAX would fail if JAX was not installed.
+  The tests will now instead be skipped if JAX cannot be imported.
+  [(#1066)](https://github.com/PennyLaneAI/pennylane/pull/1066)
+
+<h3>Documentation</h3>
+
+* Updates mentions of `generate_hamiltonian` to `molecular_hamiltonian` in the
+  docstrings of the `ExpvalCost` and `Hamiltonian` classes.
+  [(#1077)](https://github.com/PennyLaneAI/pennylane/pull/1077)
+
+<h3>Contributors</h3>
+
+This release contains contributions from (in alphabetical order):
+
+Thomas Bromley, Josh Izaac, Antal Száva.
+
+# Release 0.14.0
 
 <h3>New features since last release</h3>
 

pennylane/_version.py

@@ -16,4 +16,4 @@
 Version number (major.minor.patch[-label])
 """
 
-__version__ = "0.14.0"
+__version__ = "0.14.1"

pennylane/devices/default_qubit_autograd.py

@@ -157,11 +157,18 @@ def _get_unitary_matrix(self, unitary):
             the unitary in the computational basis, or, in the case of a diagonal unitary,
             a 1D array representing the matrix diagonal.
         """
-        op_name = unitary.name
+        op_name = unitary.name.split(".inv")[0]
+
         if op_name in self.parametric_ops:
             if op_name == "MultiRZ":
-                return self.parametric_ops[unitary.name](*unitary.parameters, len(unitary.wires))
-            return self.parametric_ops[unitary.name](*unitary.parameters)
+                mat = self.parametric_ops[op_name](*unitary.parameters, len(unitary.wires))
+            else:
+                mat = self.parametric_ops[op_name](*unitary.parameters)
+
+            if unitary.inverse:
+                mat = self._transpose(self._conj(mat))
+
+            return mat
 
         if isinstance(unitary, DiagonalOperation):
             return unitary.eigvals

pennylane/devices/default_qubit_jax.py

@@ -204,11 +204,18 @@ def _get_unitary_matrix(self, unitary):
             the unitary in the computational basis, or, in the case of a diagonal unitary,
             a 1D array representing the matrix diagonal.
         """
-        op_name = unitary.name
+        op_name = unitary.name.split(".inv")[0]
+
         if op_name in self.parametric_ops:
             if op_name == "MultiRZ":
-                return self.parametric_ops[unitary.name](*unitary.parameters, len(unitary.wires))
-            return self.parametric_ops[unitary.name](*unitary.parameters)
+                mat = self.parametric_ops[op_name](*unitary.parameters, len(unitary.wires))
+            else:
+                mat = self.parametric_ops[op_name](*unitary.parameters)
+
+            if unitary.inverse:
+                mat = self._transpose(self._conj(mat))
+
+            return mat
 
         if isinstance(unitary, DiagonalOperation):
             return unitary.eigvals

pennylane/devices/default_qubit_tf.py

@@ -214,10 +214,18 @@ def _get_unitary_matrix(self, unitary):
             the return type will be a ``np.ndarray``. For parametric unitaries, a ``tf.Tensor``
             object will be returned.
         """
-        if unitary.name in self.parametric_ops:
-            if unitary.name == "MultiRZ":
-                return self.parametric_ops[unitary.name](unitary.parameters, len(unitary.wires))
-            return self.parametric_ops[unitary.name](*unitary.parameters)
+        op_name = unitary.name.split(".inv")[0]
+
+        if op_name in self.parametric_ops:
+            if op_name == "MultiRZ":
+                mat = self.parametric_ops[op_name](*unitary.parameters, len(unitary.wires))
+            else:
+                mat = self.parametric_ops[op_name](*unitary.parameters)
+
+            if unitary.inverse:
+                mat = self._transpose(self._conj(mat))
+
+            return mat
 
         if isinstance(unitary, DiagonalOperation):
             return unitary.eigvals

pennylane/tape/qnode.py

@@ -107,6 +107,11 @@ class QNode:
             and is stored and re-used for further quantum evaluations. Only set this to False
             if it is known that the underlying quantum structure is **independent of QNode input**.
 
+        max_expansion (int): The number of times the internal circuit should be expanded when
+            executed on a device. Expansion occurs when an operation or measurement is not
+            supported, and results in a gate decomposition. If any operations in the decomposition
+            remain unsupported by the device, another expansion occurs.
+
     Keyword Args:
         h=1e-7 (float): step size for the finite difference method
         order=1 (int): The order of the finite difference method to use. ``1`` corresponds
@@ -125,7 +130,14 @@ class QNode:
     # pylint:disable=too-many-instance-attributes,too-many-arguments
 
     def __init__(
-        self, func, device, interface="autograd", diff_method="best", mutable=True, **diff_options
+        self,
+        func,
+        device,
+        interface="autograd",
+        diff_method="best",
+        mutable=True,
+        max_expansion=10,
+        **diff_options,
     ):
 
         if interface is not None and interface not in self.INTERFACE_MAP:
@@ -156,7 +168,7 @@ def __init__(
         self.diff_options.update(tape_diff_options)
 
         self.dtype = np.float64
-        self.max_expansion = 2
+        self.max_expansion = max_expansion
 
     # pylint: disable=too-many-return-statements
     @staticmethod
@@ -765,7 +777,9 @@ def to_jax(self):
     INTERFACE_MAP = {"autograd": to_autograd, "torch": to_torch, "tf": to_tf, "jax": to_jax}
 
 
-def qnode(device, interface="autograd", diff_method="best", mutable=True, **diff_options):
+def qnode(
+    device, interface="autograd", diff_method="best", mutable=True, max_expansion=10, **diff_options
+):
     """Decorator for creating QNodes.
 
     This decorator is used to indicate to PennyLane that the decorated function contains a
@@ -842,6 +856,11 @@ def qnode(device, interface="autograd", diff_method="best", mutable=True, **diff
             and is stored and re-used for further quantum evaluations. Only set this to False
             if it is known that the underlying quantum structure is **independent of QNode input**.
 
+        max_expansion (int): The number of times the internal circuit should be expanded when
+            executed on a device. Expansion occurs when an operation or measurement is not
+            supported, and results in a gate decomposition. If any operations in the decomposition
+            remain unsupported by the device, another expansion occurs.
+
     Keyword Args:
         h=1e-7 (float): Step size for the finite difference method.
         order=1 (int): The order of the finite difference method to use. ``1`` corresponds
@@ -865,6 +884,7 @@ def qfunc_decorator(func):
             interface=interface,
             diff_method=diff_method,
             mutable=mutable,
+            max_expansion=max_expansion,
             **diff_options,
         )
         return update_wrapper(qn, func)

pennylane/vqe/vqe.py

@@ -42,7 +42,7 @@ class Hamiltonian:
         simplify (bool): Specifies whether the Hamiltonian is simplified upon initialization
                          (like-terms are combined). The default value is `False`.
 
-    .. seealso:: :class:`~.ExpvalCost`, :func:`~.generate_hamiltonian`
+    .. seealso:: :class:`~.ExpvalCost`, :func:`~.molecular_hamiltonian`
 
     **Example:**
 
@@ -66,7 +66,7 @@ class Hamiltonian:
     >>> print(H)
     (0.8) [Hermitian0'1]
 
-    Alternatively, the :func:`~.generate_hamiltonian` function from the
+    Alternatively, the :func:`~.molecular_hamiltonian` function from the
     :doc:`/introduction/chemistry` module can be used to generate a molecular
     Hamiltonian.
     """
@@ -90,8 +90,8 @@ def __init__(self, coeffs, observables, simplify=False):
                     "Could not create circuits. Some or all observables are not valid."
                 )
 
-        self._coeffs = coeffs
-        self._ops = observables
+        self._coeffs = list(coeffs)
+        self._ops = list(observables)
 
         if simplify:
             self.simplify()
@@ -396,7 +396,7 @@ class ExpvalCost:
         callable: a cost function with signature ``cost_fn(params, **kwargs)`` that evaluates
         the expectation of the Hamiltonian on the provided device(s)
 
-    .. seealso:: :class:`~.Hamiltonian`, :func:`~.generate_hamiltonian`, :func:`~.map`, :func:`~.dot`
+    .. seealso:: :class:`~.Hamiltonian`, :func:`~.molecular_hamiltonian`, :func:`~.map`, :func:`~.dot`
 
     **Example:**
 
@@ -486,6 +486,10 @@ def __init__(
         self._multiple_devices = isinstance(device, Sequence)
         """Bool: Records if multiple devices are input"""
 
+        if all(c == 0 for c in coeffs) or not coeffs:
+            self.cost_fn = lambda *args, **kwargs: np.array(0)
+            return
+
         tape_mode = qml.tape_mode_active()
         self._optimize = optimize
 

tests/conftest.py

@@ -140,6 +140,11 @@ def skip_if_no_tf_support(tf_support):
         pytest.skip("Skipped, no tf support")
 
 
+@pytest.fixture
+def skip_if_no_jax_support():
+    pytest.importorskip("jax")
+
+
 @pytest.fixture(scope="module",
                 params=[1, 2, 3])
 def seed(request):

tests/devices/test_default_qubit_autograd.py

@@ -395,6 +395,23 @@ def circuit(param):
         res = qml.jacobian(circuit)(param)
         assert np.allclose(res, np.zeros(wires **2))
 
+    def test_inverse_operation_jacobian_backprop(self, tol):
+        """Test that inverse operations work in backprop
+        mode"""
+        dev = qml.device('default.qubit.autograd', wires=1)
+
+        @qml.qnode(dev, diff_method="backprop")
+        def circuit(param):
+            qml.RY(param, wires=0).inv()
+            return qml.expval(qml.PauliX(0))
+
+        x = 0.3
+        res = circuit(x)
+        assert np.allclose(res, -np.sin(x), atol=tol, rtol=0)
+
+        grad = qml.grad(circuit)(x)
+        assert np.allclose(grad, -np.cos(x), atol=tol, rtol=0)
+
     def test_full_subsystem(self, mocker):
         """Test applying a state vector to the full subsystem"""
         dev = DefaultQubitAutograd(wires=['a', 'b', 'c'])

tests/devices/test_default_qubit_jax.py

@@ -475,6 +475,24 @@ def circuit(param):
         res = jacobian_transform(circuit)(param)
         assert jnp.allclose(res, jnp.zeros(wires ** 2))
 
+    def test_inverse_operation_jacobian_backprop(self, tol):
+        """Test that inverse operations work in backprop
+        mode"""
+        dev = qml.device('default.qubit.jax', wires=1)
+
+        @qml.qnode(dev, diff_method="backprop", interface="jax")
+        def circuit(param):
+            qml.RY(param, wires=0).inv()
+            return qml.expval(qml.PauliX(0))
+
+        x = 0.3
+        res = circuit(x)
+        assert np.allclose(res, -np.sin(x), atol=tol, rtol=0)
+
+        # Adjust grad func to be compatible when tested with both old and new cores of PennyLane
+        grad = jax.grad(lambda a: circuit(a).reshape(()))(x)
+        assert np.allclose(grad, -np.cos(x), atol=tol, rtol=0)
+
     def test_full_subsystem(self, mocker):
         """Test applying a state vector to the full subsystem"""
         dev = DefaultQubitJax(wires=["a", "b", "c"])

tests/devices/test_default_qubit_tf.py

@@ -1238,6 +1238,26 @@ def cost(params):
         )
         assert np.allclose(res.numpy(), expected_grad, atol=tol, rtol=0)
 
+    def test_inverse_operation_jacobian_backprop(self, tol):
+        """Test that inverse operations work in backprop
+        mode"""
+        dev = qml.device('default.qubit.tf', wires=1)
+
+        @qml.qnode(dev, diff_method="backprop", interface="tf")
+        def circuit(param):
+            qml.RY(param, wires=0).inv()
+            return qml.expval(qml.PauliX(0))
+
+        x = tf.Variable(0.3)
+
+        with tf.GradientTape() as tape:
+            res = circuit(x)
+
+        assert np.allclose(res, -tf.sin(x), atol=tol, rtol=0)
+
+        grad = tape.gradient(res, x)
+        assert np.allclose(grad, -tf.cos(x), atol=tol, rtol=0)
+
     @pytest.mark.parametrize("interface", ["autograd", "torch"])
     def test_error_backprop_wrong_interface(self, interface, tol):
         """Tests that an error is raised if diff_method='backprop' but not using

tests/qnn/test_cost.py

@@ -42,7 +42,9 @@ def skip_if_no_torch_support():
 
 
 @pytest.mark.parametrize("interface", ALLOWED_INTERFACES)
-@pytest.mark.usefixtures("skip_if_no_torch_support", "skip_if_no_tf_support")
+@pytest.mark.usefixtures(
+    "skip_if_no_torch_support", "skip_if_no_tf_support", "skip_if_no_jax_support"
+)
 class TestSquaredErrorLoss:
     def test_no_target(self, interface):
         with pytest.raises(ValueError, match="The target cannot be None"):