utils.py

from typing import Tuple, Union
import itertools

from openfermion import QubitOperator, count_qubits


hamiltonian_names = ["h2_4bk.data", "h2_8bk.data", "LiH_12bk.data", "BeH2_14bk.data"]


def pad_op(op: QubitOperator, num_qubit: int = None):
    if num_qubit is None:
        num_qubit = count_qubits(op)

    pad_idx = set(range(num_qubit))
    for op_label, coef in op.terms.items():
        if coef != 0:
            pad_idx -= set(itertools.chain.from_iterable(op_label))
        if len(pad_idx) == 0:
            break
    padder = QubitOperator(" ".join(f"Z{i}" for i in pad_idx))
    return op * padder


def if_single_pauli_product(operator):
    return len(str(operator).split("+")) == 1


def create_pauli_id_from_openfermion(operator: Union[QubitOperator, Tuple], n_qubit):
    if type(operator) == QubitOperator:
        assert if_single_pauli_product(operator), "input is not single product of pauli."
        terms = list(operator.terms.keys())[0]
    elif type(operator) == tuple:
        terms = operator

    qidx_list = []
    pauli_id_list = []
    plist = ["I", "X", "Y", "Z"]
    for _term in terms:
        qidx_list.append(_term[0])
        pauli_id_list.append(plist.index(_term[1]))

    ret = [0] * n_qubit
    for _qid, _pid in zip(qidx_list, pauli_id_list):
        ret[_qid] = _pid
    return ret