Remove deprecated opflow module, QuantumInstance and related utils

docs/api_redirects.txt

@@ -1,7 +1,3 @@
-qiskit.algorithms.AlgorithmError algorithms
-qiskit.algorithms.eval_observables algorithms
-qiskit.algorithms.estimate_observables algorithms
-
 qiskit.assembler.assemble_circuits assembler
 qiskit.assembler.assemble_schedules assembler
 qiskit.assembler.disassemble assembler
@@ -97,11 +93,6 @@ qiskit.converters.dagdependency_to_dag converters
 
 qiskit.dagcircuit.DAGCircuitError dagcircuit
 
-qiskit.opflow.commutator opflow
-qiskit.opflow.anti_commutator opflow
-qiskit.opflow.double_commutator opflow
-qiskit.opflow.OpflowError opflow
-
 qiskit.providers.QiskitBackendNotFoundError providers
 qiskit.providers.BackendPropertyError providers
 qiskit.providers.JobError providers

docs/apidoc/index.rst

@@ -44,17 +44,4 @@ API Reference
    transpiler_synthesis_plugins
    transpiler_builtin_plugins
    utils
-   utils_mitigation
    exceptions
-
-Deprecated Modules
-==================
-
-.. warning::
-
-   These modules are going to be removed in Qiskit 1.0. Consider pinning ``qiskit~=0.45`` in your dependencies if you need them.
-
-.. toctree::
-   :maxdepth: 1
-
-   opflow

docs/migration_guides/opflow_migration.rst

@@ -54,7 +54,7 @@ The functional equivalency can be roughly summarized as follows:
 
    * - Opflow Module
      - Alternative
-   * - Operators (:class:`~qiskit.opflow.OperatorBase`, :ref:`operator_globals`,
+   * - Operators (:class:`~qiskit.opflow.OperatorBase`, ``operator_globals``,
        :mod:`~qiskit.opflow.primitive_ops`, :mod:`~qiskit.opflow.list_ops`)
      - ``qiskit.quantum_info`` :ref:`Operators <quantum_info_operators>`
 
@@ -134,7 +134,7 @@ Operator Globals
 *Back to* `Contents`_
 
 Opflow provided shortcuts to define common single qubit states, operators, and non-parametrized gates in the
-:ref:`operator_globals` module.
+``operator_globals`` module.
 
 These were mainly used for didactic purposes or quick prototyping, and can easily be replaced by their corresponding
 :mod:`~qiskit.quantum_info` class: :class:`~qiskit.quantum_info.Pauli`, :class:`~qiskit.quantum_info.Clifford` or

qiskit/circuit/library/evolved_operator_ansatz.py

@@ -20,7 +20,6 @@
 from qiskit.circuit.parameter import Parameter
 from qiskit.circuit.quantumregister import QuantumRegister
 from qiskit.circuit.quantumcircuit import QuantumCircuit
-from qiskit.exceptions import QiskitError
 from qiskit.quantum_info import Operator, Pauli, SparsePauliOp
 from qiskit.synthesis.evolution import LieTrotter
 
@@ -44,15 +43,14 @@ def __init__(
     ):
         """
         Args:
-            operators (BaseOperator | OperatorBase | QuantumCircuit | list | None): The operators
+            operators (BaseOperator | QuantumCircuit | list | None): The operators
                 to evolve. If a circuit is passed, we assume it implements an already evolved
                 operator and thus the circuit is not evolved again. Can be a single operator
                 (circuit) or a list of operators (and circuits).
             reps: The number of times to repeat the evolved operators.
             evolution (EvolutionBase | EvolutionSynthesis | None):
                 A specification of which evolution synthesis to use for the
-                :class:`.PauliEvolutionGate`, if the operator is from :mod:`qiskit.quantum_info`
-                or an opflow converter object if the operator is from :mod:`qiskit.opflow`.
+                :class:`.PauliEvolutionGate`.
                 Defaults to first order Trotterization.
             insert_barriers: Whether to insert barriers in between each evolution.
             name: The name of the circuit.
@@ -113,13 +111,8 @@ def evolution(self):
         """The evolution converter used to compute the evolution.
 
         Returns:
-            EvolutionBase or EvolutionSynthesis: The evolution converter used to compute the evolution.
+            EvolutionSynthesis: The evolution converter used to compute the evolution.
         """
-        if self._evolution is None:
-            # pylint: disable=cyclic-import
-            from qiskit.opflow import PauliTrotterEvolution
-
-            return PauliTrotterEvolution()
 
         return self._evolution
 
@@ -128,8 +121,7 @@ def evolution(self, evol) -> None:
         """Sets the evolution converter used to compute the evolution.
 
         Args:
-            evol (EvolutionBase | EvolutionSynthesis): An evolution synthesis object or
-                opflow converter object to construct the evolution.
+            evol (EvolutionSynthesis): An evolution synthesis object
         """
         self._invalidate()
         self._evolution = evol
@@ -147,7 +139,7 @@ def operators(self):
     def operators(self, operators=None) -> None:
         """Set the operators to be evolved.
 
-        operators (Optional[Union[OperatorBase, QuantumCircuit, list]): The operators to evolve.
+        operators (Optional[Union[QuantumCircuit, list]): The operators to evolve.
             If a circuit is passed, we assume it implements an already evolved operator and thus
             the circuit is not evolved again. Can be a single operator (circuit) or a list of
             operators (and circuits).
@@ -174,21 +166,10 @@ def preferred_init_points(self):
             return np.zeros(self.reps * len(self.operators), dtype=float)
 
     def _evolve_operator(self, operator, time):
-        from qiskit.opflow import OperatorBase, EvolutionBase
 
         # pylint: disable=cyclic-import
         from qiskit.circuit.library.hamiltonian_gate import HamiltonianGate
 
-        if isinstance(operator, OperatorBase):
-            if not isinstance(self.evolution, EvolutionBase):
-                raise QiskitError(
-                    "If qiskit.opflow operators are evolved the evolution must be a "
-                    f"qiskit.opflow.EvolutionBase, not a {type(self.evolution)}."
-                )
-
-            evolved = self.evolution.convert((time * operator).exp_i())
-            return evolved.reduce().to_circuit()
-
         # if the operator is specified as matrix use exact matrix exponentiation
         if isinstance(operator, Operator):
             gate = HamiltonianGate(operator, time)
@@ -254,17 +235,11 @@ def _validate_prefix(parameter_prefix, operators):
 
 
 def _is_pauli_identity(operator):
-    from qiskit.opflow import PauliOp, PauliSumOp
-
-    if isinstance(operator, PauliSumOp):
-        operator = operator.to_pauli_op()
     if isinstance(operator, SparsePauliOp):
         if len(operator.paulis) == 1:
             operator = operator.paulis[0]  # check if the single Pauli is identity below
         else:
             return False
-    if isinstance(operator, PauliOp):
-        operator = operator.primitive
     if isinstance(operator, Pauli):
         return not np.any(np.logical_or(operator.x, operator.z))
     return False

qiskit/circuit/library/pauli_evolution.py

@@ -50,7 +50,10 @@ class PauliEvolutionGate(Gate):
 
         from qiskit.circuit import QuantumCircuit
         from qiskit.circuit.library import PauliEvolutionGate
-        from qiskit.opflow import I, Z, X
+        from qiskit.quantum_info import SparsePauliOp
+
+        X = SparsePauliOp("X")
+        Z = SparsePauliOp("Z")
 
         # build the evolution gate
         operator = (Z ^ Z) - 0.1 * (X ^ I)
@@ -86,7 +89,7 @@ def __init__(
     ) -> None:
         """
         Args:
-            operator (Pauli | PauliOp | SparsePauliOp | PauliSumOp | list):
+            operator (Pauli | SparsePauliOp | list):
                 The operator to evolve. Can also be provided as list of non-commuting
                 operators where the elements are sums of commuting operators.
                 For example: ``[XY + YX, ZZ + ZI + IZ, YY]``.
@@ -147,22 +150,9 @@ def validate_parameter(
 
 
 def _to_sparse_pauli_op(operator):
-    """Cast the operator to a SparsePauliOp.
+    """Cast the operator to a SparsePauliOp."""
 
-    For Opflow objects, return a global coefficient that must be multiplied to the evolution time.
-    Since this coefficient might contain unbound parameters it cannot be absorbed into the
-    coefficients of the SparsePauliOp.
-    """
-    # pylint: disable=cyclic-import
-    from qiskit.opflow import PauliSumOp, PauliOp
-
-    if isinstance(operator, PauliSumOp):
-        sparse_pauli = operator.primitive
-        sparse_pauli._coeffs *= operator.coeff
-    elif isinstance(operator, PauliOp):
-        sparse_pauli = SparsePauliOp(operator.primitive)
-        sparse_pauli._coeffs *= operator.coeff
-    elif isinstance(operator, Pauli):
+    if isinstance(operator, Pauli):
         sparse_pauli = SparsePauliOp(operator)
     elif isinstance(operator, SparsePauliOp):
         sparse_pauli = operator