Replace PauliSumOp with SparsePauliOp

qiskit_nature/second_q/algorithms/excited_states_solvers/excited_states_eigensolver.py

@@ -20,6 +20,7 @@
 
 from qiskit.algorithms.eigensolvers import Eigensolver
 from qiskit.opflow import PauliSumOp
+from qiskit.quantum_info import SparsePauliOp
 
 from qiskit_nature.second_q.mappers import QubitConverter, QubitMapper
 from qiskit_nature.second_q.operators import SparseLabelOp
@@ -63,8 +64,8 @@ def solver(self, solver: Union[Eigensolver, EigensolverFactory]) -> None:
     def get_qubit_operators(
         self,
         problem: BaseProblem,
-        aux_operators: Optional[dict[str, Union[SparseLabelOp, PauliSumOp]]] = None,
-    ) -> Tuple[PauliSumOp, Optional[dict[str, PauliSumOp]]]:
+        aux_operators: Optional[dict[str, SparseLabelOp | PauliSumOp | SparsePauliOp]] = None,
+    ) -> Tuple[PauliSumOp | SparsePauliOp, Optional[dict[str, PauliSumOp | SparsePauliOp]]]:
         # Note that ``aux_ops`` contains not only the transformed ``aux_operators`` passed by the
         # user but also additional ones from the transformation
         main_second_q_op, aux_second_q_ops = problem.second_q_ops()
@@ -127,7 +128,7 @@ def get_qubit_operators(
     def solve(
         self,
         problem: BaseProblem,
-        aux_operators: Optional[dict[str, Union[SparseLabelOp, PauliSumOp]]] = None,
+        aux_operators: Optional[dict[str, SparseLabelOp | PauliSumOp | SparsePauliOp]] = None,
     ) -> EigenstateResult:
         """Compute Ground and Excited States properties.
 

qiskit_nature/second_q/algorithms/excited_states_solvers/excited_states_solver.py

@@ -15,9 +15,10 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
-from typing import Optional, Union, Tuple
+from typing import Optional, Tuple
 
 from qiskit.opflow import PauliSumOp
+from qiskit.quantum_info import SparsePauliOp
 
 from qiskit_nature.second_q.operators import SparseLabelOp
 from qiskit_nature.second_q.problems import BaseProblem
@@ -31,7 +32,7 @@ class ExcitedStatesSolver(ABC):
     def solve(
         self,
         problem: BaseProblem,
-        aux_operators: Optional[dict[str, Union[SparseLabelOp, PauliSumOp]]] = None,
+        aux_operators: Optional[dict[str, SparseLabelOp | PauliSumOp | SparsePauliOp]] = None,
     ) -> EigenstateResult:
         r"""Compute the excited states energies of the molecule that was supplied via the driver.
 
@@ -54,8 +55,8 @@ def solver(self):
     def get_qubit_operators(
         self,
         problem: BaseProblem,
-        aux_operators: Optional[dict[str, Union[SparseLabelOp, PauliSumOp]]] = None,
-    ) -> Tuple[PauliSumOp, Optional[dict[str, PauliSumOp]]]:
+        aux_operators: Optional[dict[str, SparseLabelOp | PauliSumOp]] = None,
+    ) -> Tuple[PauliSumOp | SparseLabelOp, Optional[dict[str, PauliSumOp | SparseLabelOp]]]:
         """Gets the operator and auxiliary operators, and transforms the provided auxiliary operators
         using a ``QubitConverter`` or ``QubitMapper``.
         If the user-provided ``aux_operators`` contain a name which clashes with an internally

qiskit_nature/second_q/algorithms/excited_states_solvers/qeom_electronic_ops_builder.py

@@ -17,6 +17,7 @@
 from typing import Callable, Dict, List, Tuple
 
 from qiskit.opflow import PauliSumOp
+from qiskit.quantum_info import SparsePauliOp
 from qiskit.tools import parallel_map
 from qiskit.utils import algorithm_globals
 
@@ -38,7 +39,7 @@ def build_electronic_ops(
     ],
     qubit_converter: QubitConverter | QubitMapper,
 ) -> Tuple[
-    Dict[str, PauliSumOp],
+    Dict[str, PauliSumOp | SparsePauliOp],
     Dict[str, List[bool]],
     Dict[str, Tuple[Tuple[int, ...], Tuple[int, ...]]],
 ]:
@@ -71,7 +72,7 @@ def build_electronic_ops(
     size = len(excitations_list)
 
     # build all hopping operators
-    hopping_operators: Dict[str, PauliSumOp] = {}
+    hopping_operators: Dict[str, PauliSumOp | SparsePauliOp] = {}
     type_of_commutativities: Dict[str, List[bool]] = {}
     excitation_indices: Dict[str, Tuple[Tuple[int, ...], Tuple[int, ...]]] = {}
     to_be_executed_list = []
@@ -102,7 +103,7 @@ def _build_single_hopping_operator(
     excitation: Tuple[Tuple[int, ...], Tuple[int, ...]],
     num_spatial_orbitals: int,
     qubit_converter: QubitConverter | QubitMapper,
-) -> Tuple[PauliSumOp, List[bool]]:
+) -> Tuple[PauliSumOp | SparsePauliOp, List[bool]]:
     label = []
     for occ in excitation[0]:
         label.append(f"+_{occ}")

qiskit_nature/second_q/algorithms/excited_states_solvers/qeom_vibrational_ops_builder.py

@@ -17,6 +17,7 @@
 from typing import Callable, Dict, List, Tuple
 
 from qiskit.opflow import PauliSumOp
+from qiskit.quantum_info import SparsePauliOp
 from qiskit.tools import parallel_map
 from qiskit.utils import algorithm_globals
 
@@ -36,7 +37,7 @@ def build_vibrational_ops(
     ],
     qubit_converter: QubitConverter | QubitMapper,
 ) -> Tuple[
-    Dict[str, PauliSumOp],
+    Dict[str, PauliSumOp | SparsePauliOp],
     Dict[str, List[bool]],
     Dict[str, Tuple[Tuple[int, ...], Tuple[int, ...]]],
 ]:
@@ -61,7 +62,7 @@ def build_vibrational_ops(
     excitations_list = ansatz._get_excitation_list()
     size = len(excitations_list)
 
-    hopping_operators: Dict[str, PauliSumOp] = {}
+    hopping_operators: Dict[str, PauliSumOp | SparsePauliOp] = {}
     excitation_indices: Dict[str, Tuple[Tuple[int, ...], Tuple[int, ...]]] = {}
     to_be_executed_list = []
     for idx in range(size):

qiskit_nature/second_q/algorithms/ground_state_solvers/ground_state_solver.py

@@ -19,13 +19,14 @@
 
 from qiskit.opflow import PauliSumOp
 from qiskit.quantum_info.operators.base_operator import BaseOperator
+from qiskit.quantum_info import SparsePauliOp
 
 from qiskit_nature.second_q.operators import SparseLabelOp
 from qiskit_nature.second_q.mappers import QubitConverter, QubitMapper
 from qiskit_nature.second_q.problems import BaseProblem
 from qiskit_nature.second_q.problems import EigenstateResult
 
-QubitOperator = Union[BaseOperator, PauliSumOp]
+QubitOperator = Union[BaseOperator, PauliSumOp, SparsePauliOp]
 
 
 class GroundStateSolver(ABC):

qiskit_nature/second_q/circuit/library/initial_states/hartree_fock.py

@@ -16,7 +16,7 @@
 import numpy as np
 from qiskit import QuantumRegister
 from qiskit.circuit.library import BlueprintCircuit
-from qiskit.opflow import PauliSumOp
+from qiskit.quantum_info import SparsePauliOp
 from qiskit.utils.validation import validate_min
 
 from qiskit_nature.second_q.mappers import (
@@ -241,7 +241,7 @@ def hartree_fock_bitstring_mapped(
     )
 
     # map the `FermionicOp` to a qubit operator
-    qubit_op: PauliSumOp
+    qubit_op: SparsePauliOp
     if isinstance(qubit_converter, QubitConverter):
         if match_convert:
             qubit_op = qubit_converter.convert_match(bitstr_op, check_commutes=False)
@@ -254,10 +254,13 @@ def hartree_fock_bitstring_mapped(
     else:
         qubit_op = qubit_converter.map(bitstr_op)
 
+    if not isinstance(qubit_op, SparsePauliOp):
+        qubit_op = qubit_op.primitive
+
     # We check the mapped operator `x` part of the paulis because we want to have particles
     # i.e. True, where the initial state introduced a creation (`+`) operator.
     bits = []
-    for bit in qubit_op.primitive.paulis.x[0]:
+    for bit in qubit_op.paulis.x[0]:
         bits.append(bit)
 
     return bits

qiskit_nature/second_q/circuit/library/initial_states/vscf.py

@@ -20,7 +20,7 @@
 
 from qiskit import QuantumRegister
 from qiskit.circuit.library import BlueprintCircuit
-from qiskit.opflow import PauliSumOp
+from qiskit.quantum_info import SparsePauliOp
 from qiskit_nature.second_q.mappers import DirectMapper
 from qiskit_nature.second_q.mappers import QubitConverter, QubitMapper, TaperedQubitMapper
 from qiskit_nature.second_q.operators import VibrationalOp
@@ -196,7 +196,7 @@ def vscf_bitstring_mapped(
         num_modals=num_modals,
     )
     # map the `VibrationalOp` to a qubit operator
-    qubit_op: PauliSumOp
+    qubit_op: SparsePauliOp
     if isinstance(qubit_converter, QubitConverter):
         qubit_op = qubit_converter.convert_match(bitstr_op, check_commutes=False)
     elif isinstance(qubit_converter, TaperedQubitMapper):
@@ -206,10 +206,13 @@ def vscf_bitstring_mapped(
     else:
         qubit_op = qubit_converter.map(bitstr_op)
 
+    if not isinstance(qubit_op, SparsePauliOp):
+        qubit_op = qubit_op.primitive
+
     # We check the mapped operator `x` part of the paulis because we want to have particles
     # i.e. True, where the initial state introduced a creation (`+`) operator.
     bits = []
-    for bit in qubit_op.primitive.paulis.x[0]:
+    for bit in qubit_op.paulis.x[0]:
         bits.append(bit)
 
     return bits

qiskit_nature/second_q/mappers/bksf.py

@@ -19,10 +19,13 @@
 import numpy as np
 
 from qiskit.opflow import PauliSumOp
-from qiskit.quantum_info.operators import Pauli, SparsePauliOp
+from qiskit.quantum_info import SparsePauliOp
+from qiskit.quantum_info.operators import Pauli
 
+from qiskit_nature import settings
 from qiskit_nature.second_q.operators import FermionicOp
 from .fermionic_mapper import FermionicMapper
+from .qubit_mapper import QubitOperator
 
 
 class BravyiKitaevSuperFastMapper(FermionicMapper):
@@ -38,7 +41,7 @@ class BravyiKitaevSuperFastMapper(FermionicMapper):
 
     def _map_single(
         self, second_q_op: FermionicOp, *, register_length: int | None = None
-    ) -> PauliSumOp:
+    ) -> QubitOperator:
         if register_length is None:
             register_length = second_q_op.register_length
 
@@ -55,7 +58,7 @@ def _map_single(
         coeffs = sparse_pauli.coeffs[indices]
         sorted_sparse_pauli = SparsePauliOp(table, coeffs)
 
-        return PauliSumOp(sorted_sparse_pauli)
+        return PauliSumOp(sorted_sparse_pauli) if settings.use_pauli_sum_op else sorted_sparse_pauli
 
 
 class TermType(Enum):

qiskit_nature/second_q/mappers/direct_mapper.py

@@ -27,9 +27,8 @@
 class DirectMapper(VibrationalMapper):
     """The Direct mapper.
 
-    This mapper maps a :class:`~.VibrationalOp` to a
-    :class:`~qiskit.opflow.primitive_ops.PauliSumOp`. In doing so, each modal
-    of the the ``VibrationalOp`` gets mapped to a single qubit.
+    This mapper maps a :class:`~.VibrationalOp` to a qubit operator.In doing so, each modal of the
+    ``VibrationalOp`` gets mapped to a single qubit.
     """
 
     @classmethod

qiskit_nature/second_q/mappers/fermionic_mapper.py

@@ -14,11 +14,9 @@
 
 from __future__ import annotations
 
-from qiskit.opflow.primitive_ops import PauliSumOp
-
 from qiskit_nature.second_q.operators import FermionicOp
 
-from .qubit_mapper import ListOrDictType, QubitMapper
+from .qubit_mapper import ListOrDictType, QubitMapper, QubitOperator
 
 
 class FermionicMapper(QubitMapper):
@@ -29,5 +27,5 @@ def map(
         second_q_ops: FermionicOp | ListOrDictType[FermionicOp],
         *,
         register_length: int | None = None,
-    ) -> PauliSumOp | ListOrDictType[PauliSumOp]:
+    ) -> QubitOperator | ListOrDictType[QubitOperator]:
         return super().map(second_q_ops, register_length=register_length)

qiskit_nature/second_q/mappers/interleaved_qubit_mapper.py

@@ -17,9 +17,11 @@
 from qiskit.opflow import PauliSumOp
 from qiskit.quantum_info import SparsePauliOp
 
+from qiskit_nature import settings
 from qiskit_nature.second_q.operators import FermionicOp
 
 from .fermionic_mapper import FermionicMapper
+from .qubit_mapper import QubitOperator
 
 
 class InterleavedQubitMapper(FermionicMapper):
@@ -94,7 +96,7 @@ def __init__(self, mapper: FermionicMapper):
 
     def _map_single(
         self, second_q_op: FermionicOp, *, register_length: int | None = None
-    ) -> PauliSumOp:
+    ) -> QubitOperator:
         blocked_op = self.mapper._map_single(second_q_op, register_length=register_length).primitive
 
         def blocked_to_interleaved(label: str) -> str:
@@ -104,4 +106,4 @@ def blocked_to_interleaved(label: str) -> str:
             [(blocked_to_interleaved(label), coeff) for label, coeff in blocked_op.to_list()]
         )
 
-        return PauliSumOp(interleaved_op)
+        return PauliSumOp(interleaved_op) if settings.use_pauli_sum_op else interleaved_op

qiskit_nature/second_q/mappers/linear_mapper.py

@@ -22,16 +22,21 @@
 import numpy as np
 
 from qiskit.opflow import PauliSumOp
-from qiskit.quantum_info.operators import Pauli, SparsePauliOp
+from qiskit.quantum_info import SparsePauliOp
+from qiskit.quantum_info.operators import Pauli
 
+from qiskit_nature import settings
 from qiskit_nature.second_q.operators import SpinOp
+from .qubit_mapper import QubitOperator
 from .spin_mapper import SpinMapper
 
 
 class LinearMapper(SpinMapper):
     """The Linear spin-to-qubit mapping."""
 
-    def _map_single(self, second_q_op: SpinOp, *, register_length: int | None = None) -> PauliSumOp:
+    def _map_single(
+        self, second_q_op: SpinOp, *, register_length: int | None = None
+    ) -> QubitOperator:
         if register_length is None:
             register_length = second_q_op.register_length
 
@@ -55,8 +60,7 @@ def _map_single(self, second_q_op: SpinOp, *, register_length: int | None = None
             qubit_ops_list.append(coeff * reduce(operator.xor, reversed(operatorlist)))
 
         qubit_op = reduce(operator.add, qubit_ops_list)
-
-        return qubit_op
+        return qubit_op if settings.use_pauli_sum_op else qubit_op.primitive.simplify()
 
     def _linear_encoding(self, spin: Fraction | float) -> list[PauliSumOp]:
         """

qiskit_nature/second_q/mappers/logarithmic_mapper.py

@@ -22,9 +22,12 @@
 import numpy as np
 
 from qiskit.opflow import PauliSumOp
-from qiskit.quantum_info.operators import SparsePauliOp, Operator
+from qiskit.quantum_info import SparsePauliOp
+from qiskit.quantum_info.operators import Operator
 
+from qiskit_nature import settings
 from qiskit_nature.second_q.operators import SpinOp
+from .qubit_mapper import QubitOperator
 from .spin_mapper import SpinMapper
 
 
@@ -71,7 +74,9 @@ def __init__(self, *, padding: float = 1, embed_upper: bool = True) -> None:
         self._padding = padding
         self._embed_upper = embed_upper
 
-    def _map_single(self, second_q_op: SpinOp, *, register_length: int | None = None) -> PauliSumOp:
+    def _map_single(
+        self, second_q_op: SpinOp, *, register_length: int | None = None
+    ) -> QubitOperator:
         """Map spins to qubits using the Logarithmic encoding.
 
         Args:
@@ -104,7 +109,7 @@ def _map_single(self, second_q_op: SpinOp, *, register_length: int | None = None
 
         qubit_op = reduce(operator.add, qubit_ops_list)
 
-        return qubit_op
+        return qubit_op if settings.use_pauli_sum_op else qubit_op.primitive
 
     def _logarithmic_encoding(
         self, spin: Fraction | int

qiskit_nature/second_q/mappers/parity_mapper.py

@@ -25,9 +25,11 @@
 from qiskit.quantum_info.analysis.z2_symmetries import Z2Symmetries
 from qiskit.quantum_info.operators import Pauli, PauliList, SparsePauliOp
 
+from qiskit_nature import settings
 from qiskit_nature.deprecation import deprecate_arguments, deprecate_property
 from qiskit_nature.second_q.operators import FermionicOp
 from .fermionic_mapper import FermionicMapper
+from .qubit_mapper import QubitOperator
 
 logger = logging.getLogger(__name__)
 
@@ -131,10 +133,11 @@ def _two_qubit_reduce(self, operator: SparsePauliOp) -> SparsePauliOp:
 
     def _map_single(
         self, second_q_op: FermionicOp, *, register_length: int | None = None
-    ) -> PauliSumOp:
-        mapped_op = ParityMapper.mode_based_mapping(
-            second_q_op, register_length=register_length
-        ).primitive
+    ) -> QubitOperator:
+        mapped_op = ParityMapper.mode_based_mapping(second_q_op, register_length=register_length)
+
+        if isinstance(mapped_op, PauliSumOp):
+            mapped_op = mapped_op.primitive
 
         reduced_op = mapped_op
         if self.num_particles is not None:
@@ -147,4 +150,4 @@ def _map_single(
                     mapped_op.num_qubits,
                 )
 
-        return PauliSumOp(reduced_op)
+        return PauliSumOp(reduced_op) if settings.use_pauli_sum_op else reduced_op