Add qubit_properties to Target class

qiskit/providers/backend.py

@@ -474,12 +474,25 @@ def qubit_properties(
                 be a single integer for 1 qubit or a list of qubits and a list
                 of :class:`~qiskit.provider.QubitProperties` objects will be
                 returned in the same order
+        Returns:
+            qubit_properties: The :class:`~.QubitProperties` object for the
+            specified qubit. If a list of qubits is provided a list will be
+            returned. If properties are missing for a qubit this can be
+            ``None``.
 
-        raises:
+        Raises:
             NotImplementedError: if the backend doesn't support querying the
                 qubit properties
         """
-        raise NotImplementedError
+        # Since the target didn't always have a qubit properties attribute
+        # to ensure the behavior here is backwards compatible with earlier
+        # BacekendV2 implementations where this would raise a NotImplemented
+        # error.
+        if self.target.qubit_properties is None:
+            raise NotImplementedError
+        if isinstance(qubit, int):
+            return self.target.qubit_properties[qubit]
+        return [self.target.qubit_properties[q] for q in qubit]
 
     def drive_channel(self, qubit: int):
         """Return the drive channel for the given qubit.

qiskit/test/mock/fake_backend_v2.py

@@ -46,7 +46,11 @@ def __init__(self):
             online_date=datetime.datetime.utcnow(),
             backend_version="0.0.1",
         )
-        self._target = Target()
+        self._qubit_properties = [
+            QubitProperties(t1=63.48783e-6, t2=112.23246e-6, frequency=5.17538e9),
+            QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
+        ]
+        self._target = Target(qubit_properties=self._qubit_properties)
         self._theta = Parameter("theta")
         self._phi = Parameter("phi")
         self._lam = Parameter("lambda")
@@ -79,10 +83,6 @@ def __init__(self):
         }
         self._target.add_instruction(ECRGate(), ecr_props)
         self.options.set_validator("shots", (1, 4096))
-        self._qubit_properties = {
-            0: QubitProperties(t1=63.48783e-6, t2=112.23246e-6, frequency=5.17538e9),
-            1: QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
-        }
 
     @property
     def target(self):
@@ -99,6 +99,10 @@ def _default_options(cls):
     def run(self, run_input, **options):
         raise NotImplementedError
 
+
+class FakeBackendV2LegacyQubitProps(FakeBackendV2):
+    """Fake backend that doesn't use qubit properties via the target."""
+
     def qubit_properties(self, qubit):
         if isinstance(qubit, int):
             return self._qubit_properties[qubit]
@@ -116,7 +120,14 @@ def __init__(self, bidirectional=True):
             online_date=datetime.datetime.utcnow(),
             backend_version="0.0.1",
         )
-        self._target = Target()
+        qubit_properties = [
+            QubitProperties(t1=63.48783e-6, t2=112.23246e-6, frequency=5.17538e9),
+            QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
+            QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
+            QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
+            QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
+        ]
+        self._target = Target(qubit_properties=qubit_properties)
         self._theta = Parameter("theta")
         self._phi = Parameter("phi")
         self._lam = Parameter("lambda")
@@ -153,13 +164,6 @@ def __init__(self, bidirectional=True):
             ecr_props[(3, 2)] = InstructionProperties(duration=5.52e-9, error=0.0000232115)
         self._target.add_instruction(ECRGate(), ecr_props)
         self.options.set_validator("shots", (1, 4096))
-        self._qubit_properties = {
-            0: QubitProperties(t1=63.48783e-6, t2=112.23246e-6, frequency=5.17538e9),
-            1: QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
-            2: QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
-            3: QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
-            4: QubitProperties(t1=73.09352e-6, t2=126.83382e-6, frequency=5.26722e9),
-        }
 
     @property
     def target(self):
@@ -176,11 +180,6 @@ def _default_options(cls):
     def run(self, run_input, **options):
         raise NotImplementedError
 
-    def qubit_properties(self, qubit):
-        if isinstance(qubit, int):
-            return self._qubit_properties[qubit]
-        return [self._qubit_properties[i] for i in qubit]
-
 
 class FakeBackendSimple(BackendV2):
     """A fake simple backend that wraps BasicAer to implement run()."""

qiskit/transpiler/__init__.py

@@ -437,3 +437,4 @@
 from .instruction_durations import InstructionDurations
 from .target import Target
 from .target import InstructionProperties
+from .target import QubitProperties

qiskit/transpiler/target.py

@@ -27,6 +27,10 @@
 from qiskit.transpiler.instruction_durations import InstructionDurations
 from qiskit.transpiler.timing_constraints import TimingConstraints
 
+# import QubitProperties here to provide convenience alias for building a
+# full target
+from qiskit.providers.backend import QubitProperties  # pylint: disable=unused-import
+
 logger = logging.getLogger(__name__)
 
 
@@ -169,6 +173,7 @@ class Target(Mapping):
         "aquire_alignment",
         "_non_global_basis",
         "_non_global_strict_basis",
+        "qubit_properties",
     )
 
     def __init__(
@@ -180,6 +185,7 @@ def __init__(
         min_length=1,
         pulse_alignment=1,
         aquire_alignment=1,
+        qubit_properties=None,
     ):
         """
         Create a new Target object
@@ -208,6 +214,17 @@ def __init__(
                 resolution of measure instruction starting time. Measure
                 instruction should start at time which is a multiple of the
                 alignment value.
+            qubit_properties (list): A list of :class:`~.QubitProperties`
+                objects defining the characteristics of each qubit on the
+                target device. If specified the length of this list must match
+                the number of qubits in the target, where the index in the list
+                matches the qubit number the properties are defined for. If some
+                qubits don't have properties available you can set that entry to
+                ``None``
+        Raises:
+            ValueError: If both ``num_qubits`` and ``qubit_properties`` are both
+            defined and the value of ``num_qubits`` differs from the length of
+            ``qubit_properties``.
         """
         self.num_qubits = num_qubits
         # A mapping of gate name -> gate instance
@@ -227,6 +244,16 @@ def __init__(
         self.aquire_alignment = aquire_alignment
         self._non_global_basis = None
         self._non_global_strict_basis = None
+        if qubit_properties is not None:
+            if not self.num_qubits:
+                self.num_qubits = len(qubit_properties)
+            else:
+                if self.num_qubits != len(qubit_properties):
+                    raise ValueError(
+                        "The value of num_qubits specified does not match the "
+                        "length of the input qubit_properties list"
+                    )
+        self.qubit_properties = qubit_properties
 
     def add_instruction(self, instruction, properties=None, name=None):
         """Add a new instruction to the :class:`~qiskit.transpiler.Target`

releasenotes/notes/qubit-properties-target-6b1fb155a46cb942.yaml

@@ -0,0 +1,21 @@
+---
+features:
+  - |
+    Added a new attribute, :attr:`~.Target.qubit_properties` to the
+    :class:`~.Target` class. This attribute contains a list of
+    :class:`~.QubitProperties` objects for each qubit in the target.
+    For example::
+
+        target.qubit_properties[2]
+
+    will contain the :class:`~.QubitProperties` for qubit number 2 in the
+    target.
+
+    For :class:`~.BackendV2` authors, if you were previously defining
+    :class:`~.QubitProperties` directly on your :class:`~.BackendV2`
+    implementation by overriding :meth:`.BackendV2.qubit_properties` this
+    will still work fine. However, if you do move the definition to the 
+    underlying :class:`~.Target` object and remove the specialized
+    :meth:`.BackendV2.qubit_properties` implementation which will enable
+    using qubit properties in the transpiler and also maintain API compatibility
+    with your previous implementation

test/python/providers/test_backend_v2.py

@@ -24,7 +24,12 @@
 from qiskit.compiler.transpiler import _parse_inst_map
 from qiskit.pulse.instruction_schedule_map import InstructionScheduleMap
 from qiskit.test.base import QiskitTestCase
-from qiskit.test.mock.fake_backend_v2 import FakeBackendV2, FakeBackend5QV2
+from qiskit.test.mock.fake_backend_v2 import (
+    FakeBackendV2,
+    FakeBackend5QV2,
+    FakeBackendSimple,
+    FakeBackendV2LegacyQubitProps,
+)
 from qiskit.test.mock.fake_mumbai_v2 import FakeMumbaiFractionalCX
 from qiskit.quantum_info import Operator
 
@@ -53,6 +58,18 @@ def test_qubit_properties(self):
         self.assertEqual([126.83382e-6, 112.23246e-6], [x.t2 for x in props])
         self.assertEqual([5.26722e9, 5.17538e9], [x.frequency for x in props])
 
+    def test_legacy_qubit_properties(self):
+        """Test that qubit props work for backends not using properties in target."""
+        props = FakeBackendV2LegacyQubitProps().qubit_properties([1, 0])
+        self.assertEqual([73.09352e-6, 63.48783e-6], [x.t1 for x in props])
+        self.assertEqual([126.83382e-6, 112.23246e-6], [x.t2 for x in props])
+        self.assertEqual([5.26722e9, 5.17538e9], [x.frequency for x in props])
+
+    def test_no_qubit_properties_raises(self):
+        """Ensure that if no qubit properties are defined we raise correctly."""
+        with self.assertRaises(NotImplementedError):
+            FakeBackendSimple().qubit_properties(0)
+
     def test_option_bounds(self):
         """Test that option bounds are enforced."""
         with self.assertRaises(ValueError) as cm: