Quellcode für qiskit.opflow.converters.two_qubit_reduction

# This code is part of Qiskit.
# (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
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
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"""Z2 Symmetry Tapering Converter Class"""

import logging
from typing import List, Tuple, Union, cast

from qiskit.opflow.converters.converter_base import ConverterBase
from qiskit.opflow.operator_base import OperatorBase
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__)

[Doku]class TwoQubitReduction(ConverterBase): """ Deprecated: 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="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] else: num_alpha = num_particles // 2 num_beta = num_particles // 2 par_1 = 1 if (num_alpha + num_beta) % 2 == 0 else -1 par_2 = 1 if num_alpha % 2 == 0 else -1 self._tapering_values = [par_2, par_1]
[Doku] def convert(self, operator: OperatorBase) -> OperatorBase: """ Converts the Operator to tapered one by Z2 symmetries. Args: operator: the operator Returns: A new operator whose qubit number is reduced by 2. """ if not isinstance(operator, PauliSumOp): return operator operator = cast(PauliSumOp, operator) if operator.is_zero(): logger.info( "Operator is empty, can not do two qubit reduction. Return the empty operator back." ) return PauliSumOp.from_list([("I" * (operator.num_qubits - 2), 0)]) num_qubits = operator.num_qubits last_idx = num_qubits - 1 mid_idx = num_qubits // 2 - 1 sq_list = [mid_idx, last_idx] # build symmetries, sq_paulis: symmetries, sq_paulis = [], [] for idx in sq_list: pauli_str = ["I"] * num_qubits pauli_str[idx] = "Z" z_sym = Pauli("".join(pauli_str)[::-1]) symmetries.append(z_sym) pauli_str[idx] = "X" sq_pauli = Pauli("".join(pauli_str)[::-1]) sq_paulis.append(sq_pauli) z2_symmetries = Z2Symmetries(symmetries, sq_paulis, sq_list, self._tapering_values) return z2_symmetries.taper(operator)