TernaryTreeMapper¶

class TernaryTreeMapper(pauli_priority='ZXY')[source]¶

Bases: MajoranaMapper, ModeBasedMapper

Ternary Tree fermion-to-qubit mapping.

As described by Jiang, Kalev, Mruczkiewicz, and Neven, Quantum 4, 276 (2020), preprint at arXiv:1910.10746.

This is a mapper for MajoranaOp. For mapping FermionicOp convert to a Majorana operator first:

from qiskit_nature.second_q.operators import FermionicOp, MajoranaOp
from qiskit_nature.second_q.mappers import TernaryTreeMapper
fermionic_op = FermionicOp(...)
majorana_op = MajoranaOp.from_fermionic_op(fermionic_op)
majorana_op = majorana_op.index_order().simplify()
pauli_op = TernaryTreeMapper().map(majorana_op)

Use the Pauli priority argument (one of XYZ, XZY, YXZ, YZX, ZXY, ZYX) to influence which Pauli operators appear most frequently in the Pauli strings. The default is ‘ZXY’, due to the fact that the Z gate is usually the most directly supported gate.

Parameters:: pauli_priority (str) – Priority with which Pauli operators are assigned.
Raises:: ValueError – if pauli_priority is not one of XYZ, XZY, YXZ, YZX, ZXY, ZYX

Methods

map(second_q_ops, *, register_length=None)¶

Maps a second quantized operator or a list, dict of second quantized operators based on the current mapper.

Parameters:

second_q_ops (MajoranaOp | List[MajoranaOp | None] | Dict[str, MajoranaOp]) – A second quantized operator, or list thereof.
register_length (int | None) – when provided, this will be used to overwrite the register_length attribute of the SparseLabelOp being mapped. This is possible because the register_length is considered a lower bound in a SparseLabelOp.

Returns:

A qubit operator in the form of a SparsePauliOp, or list (resp. dict) thereof if a list (resp. dict) of second quantized operators was supplied.

Return type:

SparsePauliOp | List[SparsePauliOp | None] | Dict[str, SparsePauliOp]

mode_based_mapping(second_q_op, register_length=None)¶

Utility method to map a SparseLabelOp to a qubit operator using a pauli table.

Parameters:

second_q_op (SparseLabelOp) – the SparseLabelOp to be mapped.
register_length (int | None) – when provided, this will be used to overwrite the register_length attribute of the operator being mapped. This is possible because the register_length is considered a lower bound.

Returns:

The qubit operator corresponding to the problem-Hamiltonian in the qubit space.

Raises:

QiskitNatureError – If number length of pauli table does not match the number of operator modes, or if the operator has unexpected label content

Return type:

SparsePauliOp

pauli_table(register_length)[source]¶

This method is implemented for TernaryTreeMapper only for compatibility. TernaryTreeMapper.map only uses the sparse_pauli_operators method which overrides the corresponding method in ModeBasedMapper.

Return type:: list[tuple[PauliList | SparsePauliOp | Pauli | list | str, PauliList | SparsePauliOp | Pauli | list | str]]

sparse_pauli_operators(register_length)[source]¶

Generates the SparsePauliOp terms.

This uses pauli_table() to construct a list of operators used to translate the second-quantization symbols into qubit operators.

Parameters:: register_length (int) – the register length for which to generate the operators.
Returns:: Two lists stored in a tuple, consisting of the creation and annihilation operators, applied on the individual modes.
Return type:: tuple[list[SparsePauliOp], list[SparsePauliOp]]