Daily rc sync to master 2022-08-09 (#2914)

* Update the Hermiticity check of `qml.Hermitian` to use `qml.math` (#2895)

* fix

* changelog

* lint

* important typo fix (#2901)

* test lightning (#2903)

* Update the readme and PennyLane Logo (#2912)

* Update PennyLane Logo

* remove wordmark from readme

* update citation

* et al

* Update the logo

* replace with svg

* exclude files from pr

Co-authored-by: antalszava <antalszava@gmail.com>
Co-authored-by: David Wierichs <davidwierichs@gmail.com>
Co-authored-by: Josh Izaac <josh146@gmail.com>
Co-authored-by: GitHub Actions Bot <>
Co-authored-by: Romain Moyard <rmoyard@gmail.com>

README.md

@@ -1,9 +1,3 @@
-<p align="center">
-  <a href="https://pennylane.ai">
-    <img width=80% src="https://raw.githubusercontent.com/PennyLaneAI/pennylane/master/doc/_static/pennylane_thin.png">
-  </a>
-</p>
-
 <p align="center">
   <!-- Tests (GitHub actions) -->
   <a href="https://github.com/PennyLaneAI/pennylane/actions?query=workflow%3ATests">
@@ -147,10 +141,8 @@ PennyLane is the work of [many contributors](https://github.com/PennyLaneAI/penn
 
 If you are doing research using PennyLane, please cite [our paper](https://arxiv.org/abs/1811.04968):
 
-> Ville Bergholm, Josh Izaac, Maria Schuld, Christian Gogolin, M. Sohaib Alam, Shahnawaz Ahmed,
-> Juan Miguel Arrazola, Carsten Blank, Alain Delgado, Soran Jahangiri, Keri McKiernan, Johannes Jakob Meyer,
-> Zeyue Niu, Antal Száva, and Nathan Killoran.
-> *PennyLane: Automatic differentiation of hybrid quantum-classical computations.* 2018. arXiv:1811.04968
+> Ville Bergholm et al. *PennyLane: Automatic differentiation of hybrid quantum-classical
+> computations.* 2018. arXiv:1811.04968
 
 ## License
 

doc/conf.py

@@ -226,7 +226,8 @@
 
 # Xanadu theme options (see theme.conf for more information).
 html_theme_options = {
-    "navbar_wordmark_path": "_static/pl_wordmark.png",
+    "navbar_logo_path": "_static/logo.png",
+    "navbar_wordmark_path": "_static/pennylane.svg",
     # Specifying #19b37b is more correct but does not match the other PL websites.
     "navbar_logo_colour": "#2d7c7f",
     "navbar_home_link": "https://pennylane.ai",

doc/index.rst

@@ -116,11 +116,9 @@ If you are doing research using PennyLane, please cite
 
 .. rst-class:: admonition warning
 
-    Ville Bergholm, Josh Izaac, Maria Schuld, Christian Gogolin, M. Sohaib Alam, Shahnawaz Ahmed,
-    Juan Miguel Arrazola, Carsten Blank, Alain Delgado, Soran Jahangiri, Keri McKiernan, Johannes Jakob Meyer,
-    Zeyue Niu, Antal Száva, and Nathan Killoran.
-    *PennyLane: Automatic differentiation of hybrid quantum-classical computations.* 2018.
-    `arXiv:1811.04968 <https://arxiv.org/abs/1811.04968>`_
+    Ville Bergholm et al. *PennyLane: Automatic differentiation of hybrid
+    quantum-classical computations.* 2018. `arXiv:1811.04968
+    <https://arxiv.org/abs/1811.04968>`_
 
 Support and contribution
 ------------------------

doc/releases/changelog-0.25.0.md

@@ -624,7 +624,7 @@ of operators.
   1. The custom device inherits from `DefaultQubit`, not `QubitDevice`.
   2. The device implements custom methods in the simulation pipeline that are incompatible
      with broadcasting (for example `expval`, `apply_operation` or `analytic_probability`).
-  3. The custom device maintains the flag `"supports_broadcasting": False` in its `capabilities`
+  3. The custom device maintains the flag `"supports_broadcasting": True` in its `capabilities`
      dictionary *or* it overwrites `Device.batch_transform` without applying `broadcast_expand`
      (or both).
 
@@ -700,6 +700,11 @@ of operators.
 
 <h3>Bug fixes 🐞</h3>
 
+* Reworked the Hermiticity check in `qml.Hermitian` by using `qml.math` calls
+  because calling `.conj()` on an `EagerTensor` from TensorFlow raised an
+  error.
+  [(#2895)](https://github.com/PennyLaneAI/pennylane/pull/2895)
+
 * Updated IsingXY gate docstring.
   [(#2858)](https://github.com/PennyLaneAI/pennylane/pull/2858)
 

pennylane/ops/qubit/observables.py

@@ -16,13 +16,15 @@
 excepting the Pauli gates and Hadamard gate in ``non_parametric_ops.py``.
 """
 
-from scipy.sparse import csr_matrix
+from copy import copy
 
 import numpy as np
+from scipy.sparse import csr_matrix
 
 import pennylane as qml
 from pennylane.operation import AllWires, AnyWires, Observable
 from pennylane.wires import Wires
+
 from .matrix_ops import QubitUnitary
 
 
@@ -93,7 +95,7 @@ def compute_matrix(A):  # pylint: disable=arguments-differ
         if A.shape[0] != A.shape[1]:
             raise ValueError("Observable must be a square matrix.")
 
-        if not qml.math.allclose(A, A.conj().T):
+        if not qml.math.allclose(A, qml.math.T(qml.math.conj(A))):
             raise ValueError("Observable must be Hermitian.")
 
         return A
@@ -458,4 +460,4 @@ def compute_diagonalizing_gates(
         return []
 
     def pow(self, z):
-        return [self.__copy__()] if (isinstance(z, int) and z > 0) else super().pow(z)
+        return [copy(self)] if (isinstance(z, int) and z > 0) else super().pow(z)

tests/devices/test_default_qubit_tf.py

@@ -2112,6 +2112,22 @@ def circuit(x, w=None):
         ):
             qml.qnode(dev, diff_method="backprop", interface=interface)(circuit)
 
+    def test_hermitian_backprop(self, tol):
+        """Test that backprop with qml.Hermitian works correctly"""
+        dev = qml.device("default.qubit.tf", wires=2)
+
+        K = tf.linalg.diag([1, 2, 3, 4])
+
+        @qml.qnode(dev, interface="tf", diff_method="backprop")
+        def circuit(op):
+            qml.PauliX(0)
+            qml.PauliX(1)
+            return qml.expval(op)
+
+        res = circuit(qml.Hermitian(K, wires=range(2)))
+        assert isinstance(res, tf.Tensor)
+        assert res == 4.0
+
 
 @pytest.mark.tf
 class TestSamples:

tests/returntypes/test_new_return_types_qnode.py

@@ -20,7 +20,7 @@
 import pennylane as qml
 
 wires = [2, 3, 4]
-devices = ["default.qubit", "default.mixed"]
+devices = ["default.qubit", "lightning.qubit", "default.mixed"]
 
 
 class TestIntegrationSingleReturn:
@@ -36,7 +36,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.state()
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == (2**wires,)
@@ -52,7 +52,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.state()
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == (2**wires, 2**wires)
@@ -69,7 +69,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.density_matrix(wires=range(0, d_wires))
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == (2**d_wires, 2**d_wires)
@@ -85,7 +85,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.expval(qml.PauliZ(wires=1))
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == ()
@@ -101,7 +101,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.var(qml.PauliZ(wires=1))
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == ()
@@ -117,7 +117,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.vn_entropy(wires=0)
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == ()
@@ -133,7 +133,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.mutual_info(wires0=[0], wires1=[1])
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert res.shape == ()
@@ -158,7 +158,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.probs(op=op, wires=wires)
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         if wires is None:
@@ -246,7 +246,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.state()
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(tf.Variable(0.5))
 
         assert res.shape == (2**wires, 2**wires)
@@ -461,7 +461,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.state()
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(torch.tensor(0.5, requires_grad=True))
 
         assert res.shape == (2**wires, 2**wires)
@@ -675,7 +675,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.state()
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(jax.numpy.array(0.5))
 
         assert res.shape == (2**wires, 2**wires)
@@ -854,7 +854,7 @@ def circuit(x):
 
 wires = [([0], [1]), ([1], [0]), ([0], [0]), ([1], [1])]
 
-devices = ["default.qubit", "default.mixed"]
+devices = ["default.qubit", "lightning.qubit", "default.mixed"]
 
 
 class TestIntegrationMultipleReturns:
@@ -872,7 +872,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.expval(qml.Projector([0], wires=0)), qml.expval(qml.PauliZ(wires=1))
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert isinstance(res, tuple)
@@ -894,7 +894,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.var(qml.PauliZ(wires=0)), qml.var(qml.Hermitian([[1, 0], [0, 1]], wires=1))
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert isinstance(res, tuple)
@@ -929,7 +929,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.probs(op=op1, wires=wires1), qml.probs(op=op2, wires=wires2)
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert isinstance(res, tuple)
@@ -964,7 +964,7 @@ def circuit(x):
                 qml.expval(qml.PauliZ(wires=wires4)),
             )
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         if wires1 is None:
@@ -1045,7 +1045,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return [qml.expval(qml.PauliZ(wires=0))]
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         assert isinstance(res, list)
@@ -2354,7 +2354,7 @@ def circuit(x):
             qml.CRX(x, wires=[0, 1])
             return qml.apply(meas1), qml.apply(meas2)
 
-        qnode = qml.QNode(circuit, dev)
+        qnode = qml.QNode(circuit, dev, diff_method=None)
         res = qnode(0.5)
 
         all_shots = sum([shot_tuple.copies for shot_tuple in dev.shot_vector])