/
pauli_utils.py
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/
pauli_utils.py
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# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2020
#
# 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
# that they have been altered from the originals.
"""
PauliList utility functions.
"""
from __future__ import annotations
from qiskit.quantum_info.operators.symplectic.pauli_list import PauliList
def pauli_basis(num_qubits: int, weight: bool = False) -> PauliList:
"""Return the ordered PauliList for the n-qubit Pauli basis.
Args:
num_qubits (int): number of qubits
weight (bool): if True optionally return the basis sorted by Pauli weight
rather than lexicographic order (Default: False)
Returns:
PauliList: the Paulis for the basis
"""
pauli_1q = PauliList(["I", "X", "Y", "Z"])
if num_qubits == 1:
return pauli_1q
pauli = pauli_1q
for _ in range(num_qubits - 1):
pauli = pauli_1q.tensor(pauli)
if weight:
return pauli.sort(weight=True)
return pauli