Deprecate QuantumInstance and Opflow

qiskit/opflow/__init__.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2019, 2020.
+# (C) Copyright IBM 2019, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -17,6 +17,12 @@
 
 .. currentmodule:: qiskit.opflow
 
+.. deprecated:: 0.24.0
+
+    The :mod::`qiskit.opflow` module is deprecated and will be removed no earlier
+    than 3 months after the release date. For code migration guidelines,
+    visit https://qisk.it/opflow_migration.
+
 Operators and State functions are the building blocks of Quantum Algorithms.
 
 A library for Quantum Algorithms & Applications is more than a collection of
@@ -77,8 +83,9 @@
 Operator Base Class
 ===================
 
-The OperatorBase serves as the base class for all Operators, State functions and measurements, and
-enforces the presence and consistency of methods to manipulate these objects conveniently.
+The OperatorBase serves as the base class for all Operators, State functions
+and measurements, and enforces the presence and consistency of methods to manipulate these
+objects conveniently.
 
 .. autosummary::
    :toctree: ../stubs/
@@ -90,8 +97,8 @@
 Operator Globals
 ================
 
-The :mod:`operator_globals` is a set of immutable Operator instances that are convenient building
-blocks to reach for while working with the Operator flow.
+The :mod:`operator_globals` is a set of immutable Operator instances that are
+convenient building blocks to reach for while working with the Operator flow.
 
 One qubit Pauli operators:
    :attr:`X`, :attr:`Y`, :attr:`Z`, :attr:`I`
@@ -108,8 +115,8 @@
 Operators
 ---------
 
-The Operators submodules include the PrimitiveOp, ListOp, and StateFn class groups which
-represent the primary Operator modules.
+The Operators submodules include the PrimitiveOp, ListOp, and StateFn class
+groups which represent the primary Operator modules.
 
 .. autosummary::
     :toctree: ../stubs/
@@ -122,12 +129,12 @@
 Converters
 ----------
 
-The Converter submodules include objects which manipulate Operators, usually recursing over an
-Operator structure and changing certain Operators' representation. For example, the
-:class:`~.expectations.PauliExpectation` traverses an Operator structure, and replaces all of the
-:class:`~.state_fns.OperatorStateFn` measurements containing non-diagonal Pauli terms into
-diagonalizing circuits following by :class:`~.state_fns.OperatorStateFn` measurement containing
-only diagonal Paulis.
+The Converter submodules include objects which manipulate Operators,
+usually recursing over an Operator structure and changing certain Operators' representation.
+For example, the :class:`~.expectations.PauliExpectation` traverses an Operator structure, and
+replaces all of the :class:`~.state_fns.OperatorStateFn` measurements containing non-diagonal
+Pauli terms into diagonalizing circuits following by :class:`~.state_fns.OperatorStateFn`
+measurement containing only diagonal Paulis.
 
 .. autosummary::
     :toctree: ../stubs/

qiskit/opflow/converters/__init__.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -16,6 +16,12 @@
 
 .. currentmodule:: qiskit.opflow.converters
 
+.. deprecated:: 0.24.0
+
+    The :mod::`qiskit.opflow` module is deprecated and will be removed no earlier
+    than 3 months after the release date. For code migration guidelines,
+    visit https://qisk.it/opflow_migration.
+
 Converters are objects which manipulate Operators, usually traversing an Operator to
 change certain sub-Operators into a desired representation. Often the converted Operator is
 isomorphic or approximate to the original Operator in some way, but not always. For example,
@@ -31,6 +37,7 @@
 exponential in the number of qubits unless a clever trick is known
 (such as the use of sparse matrices).
 
+
 Note:
      Not all converters are in this module, as :mod:`~qiskit.opflow.expectations`
      and :mod:`~qiskit.opflow.evolutions` are also converters.

qiskit/opflow/converters/abelian_grouper.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -27,6 +27,7 @@
 from qiskit.opflow.primitive_ops.pauli_op import PauliOp
 from qiskit.opflow.primitive_ops.pauli_sum_op import PauliSumOp
 from qiskit.opflow.state_fns.operator_state_fn import OperatorStateFn
+from qiskit.utils.deprecation import deprecate_func
 
 
 class AbelianGrouper(ConverterBase):
@@ -41,12 +42,17 @@ class AbelianGrouper(ConverterBase):
     diagonalized together.
     """
 
+    @deprecate_func(
+        since="0.24.0",
+        additional_msg="This deprecation is part of the opflow module deprecation effort. For code migration guidelines, visit https://qisk.it/opflow_migration.",
+    )
     def __init__(self, traverse: bool = True) -> None:
         """
         Args:
             traverse: Whether to convert only the Operator passed to ``convert``, or traverse
                 down that Operator.
         """
+        super().__init__()
         self._traverse = traverse
 
     def convert(self, operator: OperatorBase) -> OperatorBase:

qiskit/opflow/converters/circuit_sampler.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -14,6 +14,7 @@
 
 
 import logging
+import warnings
 from functools import partial
 from time import time
 from typing import Any, Dict, List, Optional, Tuple, Union, cast
@@ -32,6 +33,7 @@
 from qiskit.providers import Backend
 from qiskit.utils.backend_utils import is_aer_provider, is_statevector_backend
 from qiskit.utils.quantum_instance import QuantumInstance
+from qiskit.utils.deprecation import deprecate_func
 
 logger = logging.getLogger(__name__)
 
@@ -51,6 +53,10 @@ class CircuitSampler(ConverterBase):
     you are better off using a different CircuitSampler for each Operator to avoid cache thrashing.
     """
 
+    @deprecate_func(
+        since="0.24.0",
+        additional_msg="This deprecation is part of the opflow module deprecation effort. For code migration guidelines, visit https://qisk.it/opflow_migration.",
+    )
     def __init__(
         self,
         backend: Union[Backend, QuantumInstance],
@@ -76,12 +82,17 @@ def __init__(
         Raises:
             ValueError: Set statevector or param_qobj True when not supported by backend.
         """
-        self._quantum_instance = (
-            backend if isinstance(backend, QuantumInstance) else QuantumInstance(backend=backend)
-        )
-        self._statevector = (
-            statevector if statevector is not None else self.quantum_instance.is_statevector
-        )
+        super().__init__()
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore")
+            self._quantum_instance = (
+                backend
+                if isinstance(backend, QuantumInstance)
+                else QuantumInstance(backend=backend)
+            )
+            self._statevector = (
+                statevector if statevector is not None else self.quantum_instance.is_statevector
+            )
         self._param_qobj = param_qobj
         self._attach_results = attach_results
 
@@ -105,17 +116,19 @@ def _check_quantum_instance_and_modes_consistent(self) -> None:
         Raises:
             ValueError: statevector or param_qobj are True when not supported by backend.
         """
-        if self._statevector and not is_statevector_backend(self.quantum_instance.backend):
-            raise ValueError(
-                "Statevector mode for circuit sampling requires statevector "
-                "backend, not {}.".format(self.quantum_instance.backend)
-            )
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore")
+            if self._statevector and not is_statevector_backend(self.quantum_instance.backend):
+                raise ValueError(
+                    "Statevector mode for circuit sampling requires statevector "
+                    "backend, not {}.".format(self.quantum_instance.backend)
+                )
 
-        if self._param_qobj and not is_aer_provider(self.quantum_instance.backend):
-            raise ValueError(
-                "Parameterized Qobj mode requires Aer "
-                "backend, not {}.".format(self.quantum_instance.backend)
-            )
+            if self._param_qobj and not is_aer_provider(self.quantum_instance.backend):
+                raise ValueError(
+                    "Parameterized Qobj mode requires Aer "
+                    "backend, not {}.".format(self.quantum_instance.backend)
+                )
 
     @property
     def quantum_instance(self) -> QuantumInstance:

qiskit/opflow/converters/converter_base.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -15,6 +15,7 @@
 from abc import ABC, abstractmethod
 
 from qiskit.opflow.operator_base import OperatorBase
+from qiskit.utils.deprecation import deprecate_func
 
 
 class ConverterBase(ABC):
@@ -29,6 +30,13 @@ class ConverterBase(ABC):
     in the number of qubits unless a clever trick is known (such as the use of sparse
     matrices)."""
 
+    @deprecate_func(
+        since="0.24.0",
+        additional_msg="This deprecation is part of the opflow module deprecation effort. For code migration guidelines, visit https://qisk.it/opflow_migration.",
+    )
+    def __init__(self) -> None:
+        pass
+
     @abstractmethod
     def convert(self, operator: OperatorBase) -> OperatorBase:
         """Accept the Operator and return the converted Operator

qiskit/opflow/converters/dict_to_circuit_sum.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -18,16 +18,21 @@
 from qiskit.opflow.state_fns.circuit_state_fn import CircuitStateFn
 from qiskit.opflow.state_fns.dict_state_fn import DictStateFn
 from qiskit.opflow.state_fns.vector_state_fn import VectorStateFn
+from qiskit.utils.deprecation import deprecate_func
 
 
 class DictToCircuitSum(ConverterBase):
     r"""
-    Converts ``DictStateFns`` or ``VectorStateFns`` to equivalent ``CircuitStateFns`` or sums
-    thereof. The behavior of this class can be mostly replicated by calling ``to_circuit_op`` on
-    an Operator, but with the added control of choosing whether to convert only ``DictStateFns``
+    Deprecation: Converts ``DictStateFns`` or ``VectorStateFns`` to equivalent ``CircuitStateFns``
+    or sums thereof. The behavior of this class can be mostly replicated by calling ``to_circuit_op``
+    on an Operator, but with the added control of choosing whether to convert only ``DictStateFns``
     or ``VectorStateFns``, rather than both.
     """
 
+    @deprecate_func(
+        since="0.24.0",
+        additional_msg="This deprecation is part of the opflow module deprecation effort. For code migration guidelines, visit https://qisk.it/opflow_migration.",
+    )
     def __init__(
         self, traverse: bool = True, convert_dicts: bool = True, convert_vectors: bool = True
     ) -> None:
@@ -38,6 +43,7 @@ def __init__(
             convert_dicts: Whether to convert VectorStateFn.
             convert_vectors: Whether to convert DictStateFns.
         """
+        super().__init__()
         self._traverse = traverse
         self._convert_dicts = convert_dicts
         self._convert_vectors = convert_vectors

qiskit/opflow/converters/pauli_basis_change.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -30,6 +30,7 @@
 from qiskit.opflow.state_fns.operator_state_fn import OperatorStateFn
 from qiskit.opflow.state_fns.state_fn import StateFn
 from qiskit.quantum_info import Pauli
+from qiskit.utils.deprecation import deprecate_func
 
 
 class PauliBasisChange(ConverterBase):
@@ -55,6 +56,10 @@ class PauliBasisChange(ConverterBase):
     this method, such as the placement of the CNOT chains.
     """
 
+    @deprecate_func(
+        since="0.24.0",
+        additional_msg="This deprecation is part of the opflow module deprecation effort. For code migration guidelines, visit https://qisk.it/opflow_migration.",
+    )
     def __init__(
         self,
         destination_basis: Optional[Union[Pauli, PauliOp]] = None,
@@ -83,6 +88,7 @@ def __init__(
                        beginning and ending operators are equivalent.
 
         """
+        super().__init__()
         if destination_basis is not None:
             self.destination = destination_basis  # type: ignore
         else:

qiskit/opflow/converters/two_qubit_reduction.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2020.
+# (C) Copyright IBM 2020, 2023.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -20,27 +20,33 @@
 from qiskit.opflow.primitive_ops.pauli_sum_op import PauliSumOp
 from qiskit.opflow.primitive_ops.tapered_pauli_sum_op import Z2Symmetries
 from qiskit.quantum_info import Pauli
+from qiskit.utils.deprecation import deprecate_func
 
 logger = logging.getLogger(__name__)
 
 
 class TwoQubitReduction(ConverterBase):
     """
-    Two qubit reduction converter which eliminates the central and last qubit in a list of Pauli
-    that has diagonal operators (Z,I) at those positions.
+    Two qubit reduction converter which eliminates the central and last
+    qubit in a list of Pauli that has diagonal operators (Z,I) at those positions.
 
     Chemistry specific method:
     It can be used to taper two qubits in parity and binary-tree mapped
     fermionic Hamiltonians when the spin orbitals are ordered in two spin
     sectors, (block spin order) according to the number of particles in the system.
     """
 
+    @deprecate_func(
+        since="0.24.0",
+        additional_msg="This deprecation is part of the opflow module deprecation effort. For code migration guidelines, visit https://qisk.it/opflow_migration.",
+    )
     def __init__(self, num_particles: Union[int, List[int], Tuple[int, int]]):
         """
         Args:
             num_particles: number of particles, if it is a list,
                            the first number is alpha and the second number if beta.
         """
+        super().__init__()
         if isinstance(num_particles, (tuple, list)):
             num_alpha = num_particles[0]
             num_beta = num_particles[1]