Merge branch 'master' into grover_matrix

.github/CHANGELOG.md

@@ -139,6 +139,8 @@
 and requirements-ci.txt (unpinned). This latter would be used by the CI.
   [(#1535)](https://github.com/PennyLaneAI/pennylane/pull/1535)
 
+* The `qml.ResetError` is now supported for `default.mixed` device. 
+  [(#1541)](https://github.com/PennyLaneAI/pennylane/pull/1541)
 
 <h3>Breaking changes</h3>
 
@@ -158,7 +160,8 @@ and requirements-ci.txt (unpinned). This latter would be used by the CI.
 
 This release contains contributions from (in alphabetical order):
 
-Thomas Bromley, Josh Izaac, Prateek Jain, Johannes Jakob Meyer, Akash Narayanan, Maria Schuld, Ingrid Strandberg.
+Thomas Bromley, Josh Izaac, Prateek Jain, Johannes Jakob Meyer, Akash Narayanan, Maria Schuld,
+Ingrid Strandberg, Vincent Wong.
 
 # Release 0.17.0 (current release)
 

doc/introduction/operations.rst

@@ -136,6 +136,7 @@ Noisy channels
     ~pennylane.DepolarizingChannel
     ~pennylane.BitFlip
     ~pennylane.PhaseFlip
+    ~pennylane.ResetError
     ~pennylane.QubitChannel
 
 :html:`</div>`

pennylane/devices/default_mixed.py

@@ -91,6 +91,7 @@ class DefaultMixed(QubitDevice):
         "DepolarizingChannel",
         "BitFlip",
         "PhaseFlip",
+        "ResetError",
         "QubitChannel",
         "QFT",
         "SingleExcitation",

tests/devices/test_default_mixed.py

@@ -19,7 +19,16 @@
 import pennylane as qml
 from pennylane import QubitStateVector, BasisState, DeviceError
 from pennylane.devices import DefaultMixed
-from pennylane.ops import PauliZ, CZ, PauliX, Hadamard, CNOT, AmplitudeDamping, DepolarizingChannel
+from pennylane.ops import (
+    PauliZ,
+    CZ,
+    PauliX,
+    Hadamard,
+    CNOT,
+    AmplitudeDamping,
+    DepolarizingChannel,
+    ResetError,
+)
 from pennylane.wires import Wires
 
 import numpy as np
@@ -99,11 +108,18 @@ def test_state_after_twoqubit(self, nr_wires, op, tol):
 
         assert np.allclose(dev.state, current_state, atol=tol, rtol=0)
 
-    @pytest.mark.parametrize("op", [AmplitudeDamping, DepolarizingChannel])
+    @pytest.mark.parametrize(
+        "op",
+        [
+            AmplitudeDamping(0.5, wires=0),
+            DepolarizingChannel(0.5, wires=0),
+            ResetError(0.1, 0.5, wires=0),
+        ],
+    )
     def test_state_after_channel(self, nr_wires, op, tol):
         """Tests that state is correctly retrieved after applying a channel on the first wires"""
         dev = qml.device("default.mixed", wires=nr_wires)
-        dev.apply([op(0.5, wires=0)])
+        dev.apply([op])
         current_state = np.reshape(dev._state, (2 ** nr_wires, 2 ** nr_wires))
 
         assert np.allclose(dev.state, current_state, atol=tol, rtol=0)
@@ -139,12 +155,19 @@ def test_reset_after_twoqubit(self, nr_wires, op, tol):
 
         assert np.allclose(dev._state, dev._create_basis_state(0), atol=tol, rtol=0)
 
-    @pytest.mark.parametrize("op", [AmplitudeDamping, DepolarizingChannel])
+    @pytest.mark.parametrize(
+        "op",
+        [
+            AmplitudeDamping(0.5, wires=[0]),
+            DepolarizingChannel(0.5, wires=[0]),
+            ResetError(0.1, 0.5, wires=[0]),
+        ],
+    )
     def test_reset_after_channel(self, nr_wires, op, tol):
         """Tests that state is correctly reset after applying a channel on the first
         wires"""
         dev = qml.device("default.mixed", wires=nr_wires)
-        dev.apply([op(0.5, wires=[0])])
+        dev.apply([op])
         dev.reset()
 
         assert np.allclose(dev._state, dev._create_basis_state(0), atol=tol, rtol=0)
@@ -242,17 +265,32 @@ def test_diagonal_kraus(self, ops, tol):
         assert np.allclose(dev._get_kraus(ops[0]), ops[1], atol=tol, rtol=0)
 
     p = 0.5
-    K0 = np.sqrt(1 - p) * np.eye(2)
-    K1 = np.sqrt(p / 3) * np.array([[0, 1], [1, 0]])
-    K2 = np.sqrt(p / 3) * np.array([[0, -1j], [1j, 0]])
-    K3 = np.sqrt(p / 3) * np.array([[1, 0], [0, -1]])
+    p_0, p_1 = 0.1, 0.5
 
     channel_ops = [
         (
             AmplitudeDamping(p, wires=0),
             [np.diag([1, np.sqrt(1 - p)]), np.sqrt(p) * np.array([[0, 1], [0, 0]])],
         ),
-        (DepolarizingChannel(p, wires=0), [K0, K1, K2, K3]),
+        (
+            DepolarizingChannel(p, wires=0),
+            [
+                np.sqrt(1 - p) * np.eye(2),
+                np.sqrt(p / 3) * np.array([[0, 1], [1, 0]]),
+                np.sqrt(p / 3) * np.array([[0, -1j], [1j, 0]]),
+                np.sqrt(p / 3) * np.array([[1, 0], [0, -1]]),
+            ],
+        ),
+        (
+            ResetError(p_0, p_1, wires=0),
+            [
+                np.sqrt(1 - p_0 - p_1) * np.eye(2),
+                np.sqrt(p_0) * np.array([[1, 0], [0, 0]]),
+                np.sqrt(p_0) * np.array([[0, 1], [0, 0]]),
+                np.sqrt(p_1) * np.array([[0, 0], [1, 0]]),
+                np.sqrt(p_1) * np.array([[0, 0], [0, 1]]),
+            ],
+        ),
     ]
 
     @pytest.mark.parametrize("ops", channel_ops)
@@ -276,6 +314,11 @@ class TestApplyChannel:
             DepolarizingChannel(0.5, wires=0),
             np.array([[2 / 3 + 0.0j, 0.0 + 0.0j], [0.0 + 0.0j, 1 / 3 + 0.0j]]),
         ],
+        [
+            1,
+            ResetError(0.1, 0.5, wires=0),
+            np.array([[0.5 + 0.0j, 0.0 + 0.0j], [0.0 + 0.0j, 0.5 + 0.0j]]),
+        ],
     ]
 
     @pytest.mark.parametrize("x", x_apply_channel_init)
@@ -289,7 +332,6 @@ def test_channel_init(self, x, tol):
         if op == CNOT:
             dev._apply_channel(kraus, wires=Wires([0, 1]))
         else:
-            kraus = dev._get_kraus(op)
             dev._apply_channel(kraus, wires=Wires(0))
 
         assert np.allclose(dev._state, target_state, atol=tol, rtol=0)
@@ -308,6 +350,11 @@ def test_channel_init(self, x, tol):
             DepolarizingChannel(0.5, wires=0),
             np.array([[0.5 + 0.0j, 0.0 + 0.0j], [0.0 + 0.0j, 0.5 + 0.0j]]),
         ],
+        [
+            1,
+            ResetError(0.1, 0.5, wires=0),
+            np.array([[0.3 + 0.0j, 0.0 + 0.0j], [0.0 + 0.0j, 0.7 + 0.0j]]),
+        ],
     ]
 
     @pytest.mark.parametrize("x", x_apply_channel_mixed)
@@ -323,7 +370,6 @@ def test_channel_mixed(self, x, tol):
         if op == CNOT:
             dev._apply_channel(kraus, wires=Wires([0, 1]))
         else:
-            kraus = dev._get_kraus(op)
             dev._apply_channel(kraus, wires=Wires(0))
 
         assert np.allclose(dev._state, target_state, atol=tol, rtol=0)
@@ -353,6 +399,11 @@ def test_channel_mixed(self, x, tol):
             DepolarizingChannel(0.5, wires=0),
             np.array([[0.5 + 0.0j, -1 / 6 + 0.0j], [-1 / 6 + 0.0j, 0.5 + 0.0j]]),
         ],
+        [
+            1,
+            ResetError(0.1, 0.5, wires=0),
+            np.array([[0.3 + 0.0j, -0.2 + 0.0j], [-0.2 + 0.0j, 0.7 + 0.0j]]),
+        ],
     ]
 
     @pytest.mark.parametrize("x", x_apply_channel_root)
@@ -368,7 +419,6 @@ def test_channel_root(self, x, tol):
         if op == CNOT:
             dev._apply_channel(kraus, wires=Wires([0, 1]))
         else:
-            kraus = dev._get_kraus(op)
             dev._apply_channel(kraus, wires=Wires(0))
 
         assert np.allclose(dev._state, target_state, atol=tol, rtol=0)
@@ -390,7 +440,6 @@ def test_diag_init(self, x, tol):
         if op == CZ:
             dev._apply_channel(kraus, wires=Wires([0, 1]))
         else:
-            kraus = dev._get_kraus(op)
             dev._apply_channel(kraus, wires=Wires(0))
 
         assert np.allclose(dev._state, target_state, atol=tol, rtol=0)
@@ -410,7 +459,6 @@ def test_diag_mixed(self, x, tol):
         if op == CZ:
             dev._apply_channel(kraus, wires=Wires([0, 1]))
         else:
-            kraus = dev._get_kraus(op)
             dev._apply_channel(kraus, wires=Wires(0))
 
         assert np.allclose(dev._state, target_state, atol=tol, rtol=0)
@@ -444,7 +492,6 @@ def test_diag_root(self, x, tol):
         if op == CZ:
             dev._apply_channel(kraus, wires=Wires([0, 1]))
         else:
-            kraus = dev._get_kraus(op)
             dev._apply_channel(kraus, wires=Wires(0))
 
         assert np.allclose(dev._state, target_state, atol=tol, rtol=0)

tests/ops/test_channel_ops.py

@@ -279,6 +279,40 @@ def test_p0_p1_sum_not_normalized(self):
         with pytest.raises(ValueError, match="must be between"):
             channel.ResetError(1.0, 1.0, wires=0).kraus_matrices
 
+    @pytest.mark.parametrize("angle", np.linspace(0, 2 * np.pi, 7))
+    def test_grad_reset_error(self, angle, tol):
+        """Test that gradient is computed correctly for different states. Channel
+        grad recipes are independent of channel parameter"""
+
+        dev = qml.device("default.mixed", wires=1)
+        p_0, p_1 = 0.0, 0.5
+
+        @qml.qnode(dev)
+        def circuit(p_0, p_1):
+            qml.RX(angle, wires=0)
+            qml.ResetError(p_0, p_1, wires=0)
+            return qml.expval(qml.PauliZ(0))
+
+        gradient = np.squeeze(qml.grad(circuit)(p_0, p_1))
+        assert np.allclose(
+            gradient,
+            np.array(
+                [
+                    (1 / 0.1) * (circuit(0.1, p_1) - circuit(0.0, p_1)),
+                    (1 / 0.1) * (circuit(p_0, 0.1) - circuit(p_0, 0.0)),
+                ]
+            ),
+        )
+        assert np.allclose(
+            gradient,
+            np.array(
+                [
+                    (2 * np.sin(angle / 2) * np.sin(angle / 2)),
+                    (-2 * np.cos(angle / 2) * np.cos(angle / 2)),
+                ]
+            ),
+        )
+
 
 class TestQubitChannel:
     """Tests for the quantum channel QubitChannel"""