draft: Fix how wire mapping is handled by the QuantumComputer device

doc/conf.py

@@ -20,7 +20,7 @@
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 sys.path.insert(0, os.path.abspath(".."))
 sys.path.insert(0, os.path.abspath("_ext"))
-sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath('.')), 'doc'))
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(".")), "doc"))
 
 # -- General configuration ------------------------------------------------
 
@@ -39,8 +39,8 @@
     "sphinx.ext.napoleon",
     "sphinx.ext.inheritance_diagram",
     "sphinx.ext.intersphinx",
-    'sphinx.ext.viewcode',
-    "sphinx_automodapi.automodapi"
+    "sphinx.ext.viewcode",
+    "sphinx_automodapi.automodapi",
 ]
 
 autosummary_generate = True
@@ -50,6 +50,7 @@
 
 # Add any paths that contain templates here, relative to this directory.
 from pennylane_sphinx_theme import templates_dir
+
 templates_path = [templates_dir()]
 
 # The suffix(es) of source filenames.
@@ -111,7 +112,7 @@
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-#html_theme = "sphinx_rtd_theme"
+# html_theme = "sphinx_rtd_theme"
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
@@ -135,12 +136,12 @@
 # The name of an image file (relative to this directory) to use as a favicon of
 # the docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-html_favicon = '_static/favicon.ico'
+html_favicon = "_static/favicon.ico"
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = ["_static"]
 
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied
@@ -220,7 +221,7 @@
 htmlhelp_basename = "PennyLane-Rigettidoc"
 
 # # -- Xanadu theme ---------------------------------------------------------
-html_theme = 'pennylane'
+html_theme = "pennylane"
 
 # Register the theme as an extension to generate a sitemap.xml
 # extensions.append("guzzle_sphinx_theme")
@@ -229,16 +230,15 @@
 html_theme_options = {
     "navbar_name": "PennyLane-Rigetti",
     "extra_copyrights": [
-        "TensorFlow, the TensorFlow logo, and any related marks are trademarks "
-        "of Google Inc."
+        "TensorFlow, the TensorFlow logo, and any related marks are trademarks " "of Google Inc."
     ],
     "toc_overview": True,
     "navbar_active_link": 3,
-    "google_analytics_tracking_id": "G-C480Z9JL0D"
+    "google_analytics_tracking_id": "G-C480Z9JL0D",
 }
 
-edit_on_github_project = 'PennyLaneAI/pennylane-rigetti'
-edit_on_github_branch = 'master/doc'
+edit_on_github_project = "PennyLaneAI/pennylane-rigetti"
+edit_on_github_branch = "master/doc"
 
 # -- Options for LaTeX output ---------------------------------------------
 
@@ -263,7 +263,13 @@
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).
 latex_documents = [
-    (master_doc, "PennyLane-Rigetti.tex", "PennyLane-Rigetti Documentation", "Xanadu Inc.", "manual"),
+    (
+        master_doc,
+        "PennyLane-Rigetti.tex",
+        "PennyLane-Rigetti Documentation",
+        "Xanadu Inc.",
+        "manual",
+    ),
 ]
 
 
@@ -295,10 +301,10 @@
 # ============================================================
 
 # the order in which autodoc lists the documented members
-autodoc_member_order = 'bysource'
+autodoc_member_order = "bysource"
 
 # inheritance_diagram graphviz attributes
-inheritance_node_attrs = dict(color='lightskyblue1', style='filled')
+inheritance_node_attrs = dict(color="lightskyblue1", style="filled")
 
-#autodoc_default_flags = ['members']
+# autodoc_default_flags = ['members']
 autosummary_generate = True

pennylane_rigetti/qc.py

@@ -20,17 +20,16 @@
 """
 
 from abc import ABC, abstractmethod
-from typing import Dict
 from collections import OrderedDict
+from typing import Dict
+from pennylane.utils import Iterable
+from pennylane import DeviceError, numpy as np
 
 from pyquil import Program
-from pyquil.api import QAMExecutionResult, QuantumComputer, QuantumExecutable
+from pyquil.api import QPU, QAMExecutionResult, QuantumComputer, QuantumExecutable
 from pyquil.gates import RESET, MEASURE
 from pyquil.quil import Pragma
 
-from pennylane import DeviceError, numpy as np
-from pennylane.wires import Wires
-
 from .device import RigettiDevice
 from ._version import __version__
 
@@ -45,26 +44,25 @@ class QuantumComputerDevice(RigettiDevice, ABC):
         device (str): the name of the device to initialise.
         shots (int): number of circuit evaluations/random samples used
             to estimate expectation values of observables.
-         wires (Iterable[Number, str]): Iterable that contains unique labels for the
-            qubits as numbers or strings (i.e., ``['q1', ..., 'qN']``).
-            The number of labels must match the number of qubits accessible on the backend.
-            If not provided, qubits are addressed as consecutive integers ``[0, 1, ...]``, and their number
-            is inferred from the backend.
         active_reset (bool): whether to actively reset qubits instead of waiting for
             for qubits to decay to the ground state naturally.
             Setting this to ``True`` results in a significantly faster expectation value
             evaluation when the number of shots is larger than ~1000.
 
     Keyword args:
         compiler_timeout (int): number of seconds to wait for a response from quilc (default 10).
+        wires (Optional[Union[int, Iterable[Number, str]]]): Number of qubits represented by the device, or an iterable that contains
+            unique labels for the qubits as numbers or strings (i.e., ``['q1', ..., 'qN']``). When an integer is provided, qubits
+            are addressed as consecutive integers ``[0, 1, n]`` and mapped to the first available qubits on the device. `wires` must
+            be provided for QPU devices. If not provided for a QVM device, then the number of wires is inferred from the QVM.
         execution_timeout (int): number of seconds to wait for a response from the QVM (default 10).
         parametric_compilation (bool): a boolean value of whether or not to use parametric
             compilation.
     """
     version = __version__
     author = "Rigetti Computing Inc."
 
-    def __init__(self, device, *, shots=1000, wires=None, active_reset=False, **kwargs):
+    def __init__(self, device, *, wires=None, shots=1000, active_reset=False, **kwargs):
         if shots is not None and shots <= 0:
             raise ValueError("Number of shots must be a positive integer or None.")
 
@@ -94,27 +92,43 @@ def __init__(self, device, *, shots=1000, wires=None, active_reset=False, **kwar
 
         self.qc = self.get_qc(device, **timeout_args)
 
-        self.num_wires = len(self.qc.qubits())
+        qubits = sorted(
+            [
+                qubit.id
+                for qubit in self.qc.quantum_processor.to_compiler_isa().qubits.values()
+                if qubit.dead is False
+            ]
+        )
 
         if wires is None:
-            # infer the number of modes from the device specs
-            # and use consecutive integer wire labels
-            wires = range(self.num_wires)
+            if not isinstance(self.qc.qam, QPU):
+                wires = len(qubits)
+            else:
+                raise ValueError("Wires must be specified for a QPU device. Got None for wires.")
 
         if isinstance(wires, int):
+            if wires > len(qubits):
+                raise ValueError(
+                    "Wires must not exceed available qubits on the device. ",
+                    f"The requested device only has {len(qubits)} qubits, received {wires}.",
+                )
+            wires = dict(zip(range(wires), qubits[:wires]))
+        elif isinstance(wires, Iterable):
+            if len(wires) > len(qubits):
+                raise ValueError(
+                    "Wires must not exceed available qubits on the device. ",
+                    f"The requested device only has {len(qubits)} qubits, received {len(wires)}.",
+                )
+            wires = dict(zip(wires, qubits[: len(wires)]))
+        else:
             raise ValueError(
-                f"Device has a fixed number of {self.num_wires} qubits. The wires argument can only be used "
-                "to specify an iterable of wire labels."
-            )
-
-        if self.num_wires != len(wires):
-            raise ValueError(
-                f"Device has a fixed number of {self.num_wires} qubits and "
-                f"cannot be created with {len(wires)} wires."
+                "Wires for a device must be an integer or an iterable of numbers or strings."
             )
 
-        self.wiring = dict(enumerate(self.qc.qubits()))
+        self.num_wires = len(qubits)
+        self._qubits = qubits[: len(wires)]
         self.active_reset = active_reset
+        self.wiring = wires
 
         super().__init__(wires, shots)
 
@@ -170,20 +184,13 @@ def _get_timeout_args(self, **kwargs) -> Dict[str, float]:
         return timeout_args
 
     def define_wire_map(self, wires):
-        if hasattr(self, "wiring"):
-            device_wires = Wires(self.wiring)
-        else:
-            # if no wiring given, use consecutive wire labels
-            device_wires = Wires(range(self.num_wires))
-
-        return OrderedDict(zip(wires, device_wires))
+        return OrderedDict(zip(range(len(self._qubits)), self._qubits))
 
     def apply(self, operations, **kwargs):
         """Applies the given quantum operations."""
-        prag = Program(Pragma("INITIAL_REWIRING", ['"PARTIAL"']))
+        self.prog = Program(Pragma("INITIAL_REWIRING", ['"PARTIAL"']))
         if self.active_reset:
-            prag += RESET()
-        self.prog = prag + self.prog
+            self.prog += RESET()
 
         if self.parametric_compilation:
             self.prog += self.apply_parametric_operations(operations)
@@ -193,7 +200,7 @@ def apply(self, operations, **kwargs):
         rotations = kwargs.get("rotations", [])
         self.prog += self.apply_rotations(rotations)
 
-        qubits = sorted(self.wiring.values())
+        qubits = self._qubits
         ro = self.prog.declare("ro", "BIT", len(qubits))
         for i, q in enumerate(qubits):
             self.prog.inst(MEASURE(q, ro[i]))
@@ -207,15 +214,19 @@ def apply_parametric_operations(self, operations):
             operations (List[pennylane.Operation]): quantum operations that need to be applied
 
         Returns:
-            pyquil.Prgram(): a pyQuil Program with the given operations
+            pyquil.Program(): a pyQuil Program with the given operations
         """
         prog = Program()
         # Apply the circuit operations
         for i, operation in enumerate(operations):
             # map the operation wires to the physical device qubits
             device_wires = self.map_wires(operation.wires)
 
-            if i > 0 and operation.name in ("QubitStateVector", "StatePrep", "BasisState"):
+            if i > 0 and operation.name in (
+                "QubitStateVector",
+                "StatePrep",
+                "BasisState",
+            ):
                 raise DeviceError(
                     f"Operation {operation.name} cannot be used after other Operations have already been applied "
                     f"on a {self.short_name} device."

pennylane_rigetti/qpu.py

@@ -47,13 +47,11 @@ class QPUDevice(QuantumComputerDevice):
 
     Args:
         device (str): the name of the device to initialise.
+        wires (Iterable[Number, str]): Iterable that contains unique labels for the
+            qubits as numbers or strings (i.e., ``['q1', ..., 'qN']``). The number of labels must
+            not exceed the number of qubits accessible on the backend.
         shots (int): number of circuit evaluations/random samples used
             to estimate expectation values of observables.
-         wires (Iterable[Number, str]): Iterable that contains unique labels for the
-            qubits as numbers or strings (i.e., ``['q1', ..., 'qN']``).
-            The number of labels must match the number of qubits accessible on the backend.
-            If not provided, qubits are addressed as consecutive integers ``[0, 1, ...]``, and their number
-            is inferred from the backend.
         active_reset (bool): whether to actively reset qubits instead of waiting for
             for qubits to decay to the ground state naturally.
             Setting this to ``True`` results in a significantly faster expectation value
@@ -80,9 +78,9 @@ class QPUDevice(QuantumComputerDevice):
     def __init__(
         self,
         device,
+        wires,
         *,
         shots=1000,
-        wires=None,
         active_reset=True,
         load_qc=True,
         readout_error=None,

pennylane_rigetti/qvm.py

@@ -51,9 +51,8 @@ class QVMDevice(QuantumComputerDevice):
             If a list of integers is passed, the circuit evaluations are batched over the list of shots.
         wires (Iterable[Number, str]): Iterable that contains unique labels for the
             qubits as numbers or strings (i.e., ``['q1', ..., 'qN']``).
-            The number of labels must match the number of qubits accessible on the backend.
-            If not provided, qubits are addressed as consecutive integers [0, 1, ...], and their number
-            is inferred from the backend.
+            The number of labels must match the number of qubits accessible for the selected QMV.
+            If not provided, qubits are addressed as consecutive integers [0, 1, ...], and their number is inferred from the QVM.
         noisy (bool): set to ``True`` to add noise models to your QVM.
 
     Keyword args:
@@ -65,7 +64,7 @@ class QVMDevice(QuantumComputerDevice):
     name = "Rigetti QVM Device"
     short_name = "rigetti.qvm"
 
-    def __init__(self, device, *, shots=1000, wires=None, noisy=False, **kwargs):
+    def __init__(self, device, *, wires=None, shots=1000, noisy=False, **kwargs):
         if shots is None:
             raise ValueError("QVM device cannot be used for analytic computations.")
 

tests/test_gradients.py

@@ -12,7 +12,7 @@ def test_simulator_qvm_default_agree(tol, qvm, compiler):
 
     dev1 = qml.device("default.qubit", wires=w)
     dev2 = qml.device("rigetti.wavefunction", wires=w)
-    dev3 = qml.device("rigetti.qvm", device="9q-square-qvm", shots=5000)
+    dev3 = qml.device("rigetti.qvm", wires=9, device="9q-square-qvm", shots=5000)
 
     in_state = np.zeros([w], dtype=np.int64, requires_grad=False)
     in_state[0] = 1
@@ -56,7 +56,7 @@ def test_gradient_with_custom_operator(qvm, compiler):
     w = 9
 
     dev2 = qml.device("rigetti.wavefunction", wires=w)
-    dev3 = qml.device("rigetti.qvm", device="9q-square-qvm", shots=5000)
+    dev3 = qml.device("rigetti.qvm", wires=9, device="9q-square-qvm", shots=5000)
 
     def func(x, y):
         """Reference QNode"""