Remove deprecated BackendV1 elements, including base class, `provid…

…ers.models` and `qobj` modules (#13793)

* Remove BackendV1, converters, models, qobj and update tests.

* Add reno

* Update releasenotes/notes/remove-backend-v1-et-al-cccd8f6b71a97ffc.yaml

Co-authored-by: Eli Arbel <46826214+eliarbel@users.noreply.github.com>

* Include qobj_id removal in reno. Modify result args to kwargs as specified in 1.4 deprecation warning.

* Update __init__.py

* Remove unused import

* Remove remaining qobj references (including test names and comments). Remove json decoding utils that weren't part of the public API and flew under the radar in the Fake Backend removal PR.

* Document migration of MeasLevel and MeasReturnType

* Mix malformed table

* Apply comments from Matt's review

---------

Co-authored-by: Eli Arbel <46826214+eliarbel@users.noreply.github.com>
Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

docs/apidoc/index.rst

@@ -50,7 +50,6 @@ Primitives and providers:
    providers
    providers_basic_provider
    providers_fake_provider
-   providers_models
 
 Results and visualizations:
 
@@ -83,5 +82,4 @@ Other:
 
    compiler
    exceptions
-   qobj
    utils

qiskit/compiler/transpiler.py

@@ -22,7 +22,6 @@
 from qiskit.circuit.quantumcircuit import QuantumCircuit
 from qiskit.dagcircuit import DAGCircuit
 from qiskit.providers.backend import Backend
-from qiskit.providers.backend_compat import BackendV2Converter
 from qiskit.pulse import Schedule
 from qiskit.transpiler import Layout, CouplingMap, PropertySet
 from qiskit.transpiler.basepasses import BasePass
@@ -95,21 +94,20 @@ def transpile(  # pylint: disable=too-many-return-statements
     (``basis_gates``, ``coupling_map``, ``instruction_durations``,
     ``dt`` or ``timing_constraints``). If a ``backend`` is provided together with any loose constraint
     from the list above, the loose constraint will take priority over the corresponding backend
-    constraint. This behavior is independent of whether the ``backend`` instance is of type
-    :class:`.BackendV1` or :class:`.BackendV2`, as summarized in the table below. The first column
+    constraint. This behavior is summarized in the table below. The first column
     in the table summarizes the potential user-provided constraints, and each cell shows whether
     the priority is assigned to that specific constraint input or another input
-    (`target`/`backend(V1)`/`backend(V2)`).
-
-    ============================ ========= ======================== =======================
-    User Provided                target    backend(V1)              backend(V2)
-    ============================ ========= ======================== =======================
-    **basis_gates**              target    basis_gates              basis_gates
-    **coupling_map**             target    coupling_map             coupling_map
-    **instruction_durations**    target    instruction_durations    instruction_durations
-    **dt**                       target    dt                       dt
-    **timing_constraints**       target    timing_constraints       timing_constraints
-    ============================ ========= ======================== =======================
+    (`target`/`backend(V2)`).
+
+    ============================ ========= ========================
+    User Provided                target    backend(V2)
+    ============================ ========= ========================
+    **basis_gates**              target    basis_gates
+    **coupling_map**             target    coupling_map
+    **instruction_durations**    target    instruction_durations
+    **dt**                       target    dt
+    **timing_constraints**       target    timing_constraints
+    ============================ ========= ========================
 
     Args:
         circuits: Circuit(s) to transpile
@@ -320,30 +318,6 @@ def callback_func(**kwargs):
         config = user_config.get_config()
         optimization_level = config.get("transpile_optimization_level", 2)
 
-    if backend is not None and getattr(backend, "version", 0) <= 1:
-        warnings.warn(
-            "The `transpile` function will stop supporting inputs of "
-            f"type `BackendV1` ( {backend} ) in the `backend` parameter in a future "
-            "release no earlier than 2.0. `BackendV1` is deprecated and implementations "
-            "should move to `BackendV2`.",
-            category=DeprecationWarning,
-            stacklevel=2,
-        )
-        with warnings.catch_warnings():
-            # This is a temporary conversion step to allow for a smoother transition
-            # to a fully target-based transpiler pipeline while maintaining the behavior
-            # of `transpile` with BackendV1 inputs.
-            # TODO BackendV1 is deprecated and this path can be
-            #   removed once it gets removed:
-            #   https://github.com/Qiskit/qiskit/pull/12850
-            warnings.filterwarnings(
-                "ignore",
-                category=DeprecationWarning,
-                message=r".+qiskit\.providers\.backend_compat\.BackendV2Converter.+",
-                module="qiskit",
-            )
-            backend = BackendV2Converter(backend)
-
     if (
         scheduling_method is not None
         and backend is None

qiskit/primitives/backend_estimator_v2.py

@@ -23,7 +23,7 @@
 
 from qiskit.circuit import ClassicalRegister, QuantumCircuit, QuantumRegister
 from qiskit.exceptions import QiskitError
-from qiskit.providers import BackendV1, BackendV2
+from qiskit.providers import BackendV2
 from qiskit.quantum_info import Pauli, PauliList
 from qiskit.result import Counts, Result
 from qiskit.transpiler import PassManager, PassManagerConfig
@@ -38,7 +38,7 @@
 
 def _run_circuits(
     circuits: QuantumCircuit | list[QuantumCircuit],
-    backend: BackendV1 | BackendV2,
+    backend: BackendV2,
     clear_metadata: bool = True,
     **run_options,
 ) -> tuple[list[Result], list[dict]]:
@@ -59,9 +59,7 @@ def _run_circuits(
         metadata.append(circ.metadata)
         if clear_metadata:
             circ.metadata = {}
-    if isinstance(backend, BackendV1):
-        max_circuits = getattr(backend.configuration(), "max_experiments", None)
-    elif isinstance(backend, BackendV2):
+    if isinstance(backend, BackendV2):
         max_circuits = backend.max_circuits
     else:
         raise RuntimeError("Backend version not supported")
@@ -174,7 +172,7 @@ class BackendEstimatorV2(BaseEstimatorV2):
 
     The :class:`~.BackendEstimatorV2` class is a generic implementation of the
     :class:`~.BaseEstimatorV2` interface that is used to wrap a :class:`~.BackendV2`
-    (or :class:`~.BackendV1`) object in the :class:`~.BaseEstimatorV2` API. It
+    object in the :class:`~.BaseEstimatorV2` API. It
     facilitates using backends that do not provide a native
     :class:`~.BaseEstimatorV2` implementation in places that work with
     :class:`~.BaseEstimatorV2`. However,
@@ -225,7 +223,7 @@ class BackendEstimatorV2(BaseEstimatorV2):
     def __init__(
         self,
         *,
-        backend: BackendV1 | BackendV2,
+        backend: BackendV2,
         options: dict | None = None,
     ):
         """
@@ -251,7 +249,7 @@ def options(self) -> Options:
         return self._options
 
     @property
-    def backend(self) -> BackendV1 | BackendV2:
+    def backend(self) -> BackendV2:
         """Returns the backend which this sampler object based on."""
         return self._backend
 

qiskit/primitives/backend_sampler_v2.py

@@ -36,7 +36,7 @@
 from qiskit.primitives.containers.bit_array import _min_num_bytes
 from qiskit.primitives.containers.sampler_pub import SamplerPub
 from qiskit.primitives.primitive_job import PrimitiveJob
-from qiskit.providers.backend import BackendV1, BackendV2
+from qiskit.providers.backend import BackendV2
 from qiskit.result import Result
 
 
@@ -83,7 +83,7 @@ class BackendSamplerV2(BaseSamplerV2):
 
     The :class:`~.BackendSamplerV2` class is a generic implementation of the
     :class:`~.BaseSamplerV2` interface that is used to wrap a :class:`~.BackendV2`
-    (or :class:`~.BackendV1`) object in the class :class:`~.BaseSamplerV2` API. It
+    object in the class :class:`~.BaseSamplerV2` API. It
     facilitates using backends that do not provide a native
     :class:`~.BaseSamplerV2` implementation in places that work with
     :class:`~.BaseSamplerV2`. However,
@@ -119,7 +119,7 @@ class BackendSamplerV2(BaseSamplerV2):
     def __init__(
         self,
         *,
-        backend: BackendV1 | BackendV2,
+        backend: BackendV2,
         options: dict | None = None,
     ):
         """
@@ -132,7 +132,7 @@ def __init__(
         self._options = Options(**options) if options else Options()
 
     @property
-    def backend(self) -> BackendV1 | BackendV2:
+    def backend(self) -> BackendV2:
         """Returns the backend which this sampler object based on."""
         return self._backend
 

qiskit/providers/__init__.py

@@ -21,7 +21,7 @@
 provider is anything that provides an external service to Qiskit. The typical
 example of this is a Backend provider which provides
 :class:`~qiskit.providers.Backend` objects which can be used for executing
-:class:`~qiskit.circuit.QuantumCircuit` and/or :class:`~qiskit.pulse.Schedule`
+:class:`~qiskit.circuit.QuantumCircuit`
 objects. This module contains the abstract classes which are used to define the
 interface between a provider and Qiskit.
 
@@ -82,11 +82,8 @@
    :toctree: ../stubs/
 
    Backend
-   BackendV1
    BackendV2
    QubitProperties
-   BackendV2Converter
-   convert_to_target
 
 Options
 -------
@@ -117,10 +114,8 @@
 ----------
 
 .. autoexception:: QiskitBackendNotFoundError
-.. autoexception:: BackendPropertyError
 .. autoexception:: JobError
 .. autoexception:: JobTimeoutError
-.. autoexception:: BackendConfigurationError
 
 Writing a New Backend
 =====================
@@ -559,7 +554,7 @@ def _default_options(cls):
 For some backends (mainly local simulators) the execution of circuits is a
 synchronous operation and there is no need to return a handle to a running job
 elsewhere. For sync jobs its expected that the
-:obj:`~qiskit.providers.BackendV1.run` method on the backend will block until a
+:obj:`~qiskit.providers.BackendV2.run` method on the backend will block until a
 :class:`~qiskit.result.Result` object is generated and the sync job will return
 with that inner :class:`~qiskit.result.Result` object.
 
@@ -603,7 +598,6 @@ def result(self, timeout=None, wait=5):
                 'backend_name': self._backend.configuration().backend_name,
                 'backend_version': self._backend.configuration().backend_version,
                 'job_id': self._job_id,
-                'qobj_id': ', '.join(x.name for x in self.circuits),
                 'success': True,
             })
 
@@ -666,118 +660,12 @@ def status(self):
 implementations. Also, the built-in implementations: :class:`~.Sampler`,
 :class:`~.Estimator`, :class:`~.BackendSampler`, and :class:`~.BackendEstimator`
 can serve as references/models on how to implement these as well.
-
-Migrating from BackendV1 to BackendV2
-=====================================
-
-The :obj:`~BackendV2` class re-defined user access for most properties of a
-backend to make them work with native Qiskit data structures and have flatter
-access patterns. However this means when using a provider that upgrades
-from :obj:`~BackendV1` to :obj:`~BackendV2` existing access patterns will need
-to be adjusted. It is expected for existing providers to deprecate the old
-access where possible to provide a graceful migration, but eventually users
-will need to adjust code. The biggest change to adapt to in :obj:`~BackendV2` is
-that most of the information accessible about a backend is contained in its
-:class:`~qiskit.transpiler.Target` object and the backend's attributes often query
-its :attr:`~qiskit.providers.BackendV2.target`
-attribute to return information, however in many cases the attributes only provide
-a subset of information the target can contain. For example, ``backend.coupling_map``
-returns a :class:`~qiskit.transpiler.CouplingMap` constructed from the
-:class:`~qiskit.transpiler.Target` accessible in the
-:attr:`~qiskit.providers.BackendV2.target` attribute, however the target may contain
-instructions that operate on more than two qubits (which can't be represented in a
-:class:`~qiskit.transpiler.CouplingMap`) or has instructions that only operate on
-a subset of qubits (or two qubit links for a two qubit instruction) which won't be
-detailed in the full coupling map returned by
-:attr:`~qiskit.providers.BackendV2.coupling_map`. So depending on your use case
-it might be necessary to look deeper than just the equivalent access with
-:obj:`~BackendV2`.
-
-Below is a table of example access patterns in :obj:`~BackendV1` and the new form
-with :obj:`~BackendV2`:
-
-.. list-table:: Migrate from :obj:`~BackendV1` to :obj:`~BackendV2`
-   :header-rows: 1
-
-   * - :obj:`~BackendV1`
-     - :obj:`~BackendV2`
-     - Notes
-   * - ``backend.configuration().n_qubits``
-     - ``backend.num_qubits``
-     -
-   * - ``backend.configuration().coupling_map``
-     - ``backend.coupling_map``
-     - The return from :obj:`~BackendV2` is a :class:`~qiskit.transpiler.CouplingMap` object.
-       while in :obj:`~BackendV1` it is an edge list. Also this is just a view of
-       the information contained in ``backend.target`` which may only be a subset of the
-       information contained in :class:`~qiskit.transpiler.Target` object.
-   * - ``backend.configuration().backend_name``
-     - ``backend.name``
-     -
-   * - ``backend.configuration().backend_version``
-     - ``backend.backend_version``
-     - The :attr:`~qiskit.providers.BackendV2.version` attribute represents
-       the version of the abstract :class:`~qiskit.providers.Backend` interface
-       the object implements while :attr:`~qiskit.providers.BackendV2.backend_version`
-       is metadata about the version of the backend itself.
-   * - ``backend.configuration().basis_gates``
-     - ``backend.operation_names``
-     - The :obj:`~BackendV2` return is a list of operation names contained in the
-       ``backend.target`` attribute. The :class:`~qiskit.transpiler.Target` may contain more
-       information that can be expressed by this list of names. For example, that some
-       operations only work on a subset of qubits or that some names implement the same gate
-       with different parameters.
-   * - ``backend.configuration().dt``
-     - ``backend.dt``
-     -
-   * - ``backend.configuration().dtm``
-     - ``backend.dtm``
-     -
-   * - ``backend.configuration().max_experiments``
-     - ``backend.max_circuits``
-     -
-   * - ``backend.configuration().online_date``
-     - ``backend.online_date``
-     -
-   * - ``InstructionDurations.from_backend(backend)``
-     - ``backend.instruction_durations``
-     -
-   * - ``backend.defaults().instruction_schedule_map``
-     - ``backend.instruction_schedule_map``
-     -
-   * - ``backend.properties().t1(0)``
-     - ``backend.qubit_properties(0).t1``
-     -
-   * - ``backend.properties().t2(0)``
-     - ``backend.qubit_properties(0).t2``
-     -
-   * - ``backend.properties().frequency(0)``
-     - ``backend.qubit_properties(0).frequency``
-     -
-   * - ``backend.properties().readout_error(0)``
-     - ``backend.target["measure"][(0,)].error``
-     - In :obj:`~BackendV2` the error rate for the :class:`~qiskit.circuit.library.Measure`
-       operation on a given qubit is used to model the readout error. However a
-       :obj:`~BackendV2` can implement multiple measurement types and list them
-       separately in a :class:`~qiskit.transpiler.Target`.
-   * - ``backend.properties().readout_length(0)``
-     - ``backend.target["measure"][(0,)].duration``
-     - In :obj:`~BackendV2` the duration for the :class:`~qiskit.circuit.library.Measure`
-       operation on a given qubit is used to model the readout length. However, a
-       :obj:`~BackendV2` can implement multiple measurement types and list them
-       separately in a :class:`~qiskit.transpiler.Target`.
-
-There is also a :class:`~.BackendV2Converter` class available that enables you
-to wrap a :class:`~.BackendV1` object with a :class:`~.BackendV2` interface.
 """
 
 # Providers interface
 from qiskit.providers.backend import Backend
-from qiskit.providers.backend import BackendV1
 from qiskit.providers.backend import BackendV2
 from qiskit.providers.backend import QubitProperties
-from qiskit.providers.backend_compat import BackendV2Converter
-from qiskit.providers.backend_compat import convert_to_target
 from qiskit.providers.options import Options
 from qiskit.providers.job import Job
 from qiskit.providers.job import JobV1
@@ -786,7 +674,5 @@ def status(self):
     JobError,
     JobTimeoutError,
     QiskitBackendNotFoundError,
-    BackendPropertyError,
-    BackendConfigurationError,
 )
 from qiskit.providers.jobstatus import JobStatus