Enable qpu.backend for IonQ backends (#81)

* add to changelog

* add custom backends to qpu class

* use any backend

* update changelog

* add backend classes

* make qpu classes visible

* add docstrings and remove os import

* include both backend methods in readme

* add backends to test

* remove byte 0xe2

* only use backend field + update docs and tests

* fix line length

* run black formatter

CHANGELOG.md

@@ -4,6 +4,9 @@
 
 ### Improvements 🛠
 
+* Use new `backend` field to specify `qpu`.
+  [(#81)](https://github.com/PennyLaneAI/PennyLane-IonQ/pull/81)
+
 ### Breaking changes 💔
 
 ### Deprecations 👋
@@ -16,6 +19,8 @@
 
 This release contains contributions from (in alphabetical order):
 
+Spencer Churchill
+
 ---
 # Release 0.32.0
 

README.rst

@@ -108,7 +108,7 @@ You can instantiate the IonQ devices for PennyLane as follows:
 
     import pennylane as qml
     dev1 = qml.device('ionq.simulator', wires=2, shots=1000)
-    dev2 = qml.device('ionq.qpu', wires=2, shots=1000)
+    dev2 = qml.device('ionq.qpu', backend='aria-1', wires=2, shots=1000)
 
 These devices can then be used just like other devices for the definition and evaluation of
 quantum circuits within PennyLane. For more details and ideas, see the
@@ -119,7 +119,7 @@ to the `PennyLane documentation <https://pennylane.readthedocs.io>`_.
 Contributing
 ============
 
-We welcome contributions—simply fork the PennyLane-IonQ repository, and then make a
+We welcome contributions-simply fork the PennyLane-IonQ repository, and then make a
 `pull request <https://help.github.com/articles/about-pull-requests/>`_ containing your contribution.
 All contributers to PennyLane-IonQ will be listed as contributors on the releases.
 

doc/devices.rst

@@ -38,16 +38,17 @@ directly in PennyLane by specifying ``"ionq.simulator"``:
 Trapped-Ion QPU
 ---------------
 
-This device provides access to IonQ's trapped-ion QPU.
+This device provides access to IonQ's trapped-ion QPUs.
 Once the plugin has been installed, you can use this device
-directly in PennyLane by specifying ``"ionq.qpu"``:
+directly in PennyLane by specifying ``"ionq.qpu"`` with a
+``"backend"`` from `available backends <https://docs.ionq.com/#tag/jobs>`_:
 
 .. code-block:: python
 
     import pennylane as qml
     from pennylane_ionq import ops
 
-    dev = qml.device("ionq.qpu", wires=2)
+    dev = qml.device("ionq.qpu", backend="harmony", wires=2)
 
     @qml.qnode(dev)
     def circuit(x, y):

pennylane_ionq/device.py

@@ -14,9 +14,7 @@
 """
 This module contains the device class for constructing IonQ devices for PennyLane.
 """
-import itertools
-import functools
-import warnings
+import os, warnings
 from time import sleep
 
 import numpy as np
@@ -137,7 +135,11 @@ def apply(self, operations, **kwargs):
             warnings.warn("Circuit is empty. Empty circuits return failures. Submitting anyway.")
 
         for i, operation in enumerate(operations):
-            if i > 0 and operation.name in {"BasisState", "QubitStateVector", "StatePrep"}:
+            if i > 0 and operation.name in {
+                "BasisState",
+                "QubitStateVector",
+                "StatePrep",
+            }:
                 raise DeviceError(
                     f"The operation {operation.name} is only supported at the beginning of a circuit."
                 )
@@ -269,6 +271,7 @@ class QPUDevice(IonQDevice):
             or iterable that contains unique labels for the subsystems as numbers (i.e., ``[-1, 0, 2]``)
             or strings (``['ancilla', 'q1', 'q2']``).
         gateset (str): the target gateset, either ``"qis"`` or ``"native"``.
+        backend (str): Optional specifier for an IonQ backend. Can be ``"harmony"``, ``"aria-1"``, etc.
         shots (int, list[int]): Number of circuit evaluations/random samples used to estimate
             expectation values of observables. If ``None``, the device calculates probability, expectation values,
             and variances analytically. If an integer, it specifies the number of samples to estimate these quantities.
@@ -279,8 +282,26 @@ class QPUDevice(IonQDevice):
     name = "IonQ QPU PennyLane plugin"
     short_name = "ionq.qpu"
 
-    def __init__(self, wires, *, target="qpu", gateset="qis", shots=1024, api_key=None):
-        super().__init__(wires=wires, target=target, gateset=gateset, shots=shots, api_key=api_key)
+    def __init__(
+        self,
+        wires,
+        *,
+        target="qpu",
+        backend=None,
+        gateset="qis",
+        shots=1024,
+        api_key=None,
+    ):
+        self.backend = backend
+        if self.backend is not None:
+            target += "." + self.backend
+        super().__init__(
+            wires=wires,
+            target=target,
+            gateset=gateset,
+            shots=shots,
+            api_key=api_key,
+        )
 
     def generate_samples(self):
         """Generates samples from the qpu.

setup.py

@@ -33,13 +33,11 @@
     "maintainer_email": "[email protected]",
     "url": "http://xanadu.ai",
     "license": "Apache License 2.0",
-    "packages": [
-        "pennylane_ionq"
-    ],
+    "packages": ["pennylane_ionq"],
     "entry_points": {
         "pennylane.plugins": [
             "ionq.simulator = pennylane_ionq:SimulatorDevice",
-            "ionq.qpu = pennylane_ionq:QPUDevice"
+            "ionq.qpu = pennylane_ionq:QPUDevice",
         ]
     },
     "description": "PennyLane plugin for IonQ",

tests/conftest.py

@@ -51,7 +51,7 @@
 # List of all devices that do *not* support analytic expectation
 # value computation. This generally includes hardware devices
 # and hardware simulators.
-hw_devices = [SimulatorDevice]
+hw_devices = [SimulatorDevice, QPUDevice]
 
 # List of all device shortnames
 shortnames = [d.short_name for d in analytic_devices + hw_devices]

tests/test_device.py

@@ -96,7 +96,6 @@ def mock_submit_job(*args):
             dev.apply([])
 
     def test_failedcircuit(self, monkeypatch):
-
         monkeypatch.setattr(
             requests, "post", lambda url, timeout, data, headers: (url, data, headers)
         )
@@ -182,6 +181,23 @@ def test_prob_no_results(self, d):
         dev = qml.device(d, wires=1, shots=1)
         assert dev.prob is None
 
+    @pytest.mark.parametrize(
+        "backend", ["harmony", "aria-1", "aria-2", "forte-1", None]
+    )
+    def test_backend_initialization(self, backend):
+        """Test that the device initializes with the correct backend."""
+        if backend:
+            dev = qml.device(
+                "ionq.qpu",
+                wires=2,
+                shots=1000,
+                backend=backend,
+            )
+            assert dev.backend == backend
+        else:
+            dev = qml.device("ionq.qpu", wires=2, shots=1000)
+            assert dev.backend == None
+
 
 class TestJobAttribute:
     """Tests job creation with mocked submission."""
@@ -246,7 +262,7 @@ def mock_submit_job(*args):
             pass
 
         mocker.patch("pennylane_ionq.device.IonQDevice._submit_job", mock_submit_job)
-        dev = IonQDevice(wires=(0,1,2), gateset="native")
+        dev = IonQDevice(wires=(0, 1, 2), gateset="native")
 
         with qml.tape.QuantumTape() as tape:
             GPI(0.1, wires=[0])
@@ -275,6 +291,3 @@ def mock_submit_job(*args):
             "targets": [1, 2],
             "phases": [0.2, 0.3],
         }
-
-
-