qdk_chemistry.plugins.openfermion.qubit_mapper module

OpenFermion-based qubit mappers to map electronic structure Hamiltonians to qubit operators.

This module provides an OpenFermionQubitMapper class to convert Hamiltonians to QubitHamiltonians using different mapping strategies. The encoding is determined by the MajoranaMapping passed to run().

class qdk_chemistry.plugins.openfermion.qubit_mapper.OpenFermionQubitMapper

Bases: QubitMapper

Map an electronic structure Hamiltonian to a QubitOperator using OpenFermion.

This is a third-party backend: it reads mapping.base_encoding to select the corresponding OpenFermion transform function and ignores mapping.table. The qubit operator is built from scratch using OpenFermion’s own fermion-to-qubit pipeline.

Warning

Because this backend chooses its transform by encoding name rather than from the Pauli table, it relies on the mapping’s base_encoding string being consistent with its table. This is guaranteed for factory-produced mappings (MajoranaMapping.jordan_wigner(), .bravyi_kitaev(), etc.) and is verified by cross-backend eigenvalue tests in the test suite. Manually built mappings with mismatched names will produce silently incorrect results.

Tapering-based encodings (e.g. symmetry-conserving Bravyi-Kitaev) are supported — each backend handles tapering in its own _run_impl() via the QubitMapper._taper_result() helper.

Both restricted (RHF) and unrestricted (UHF) Hamiltonians are supported. For unrestricted systems, separate alpha/beta spin channels are handled via hamiltonian_to_interaction_operator.

Supported base encodings:

• "jordan-wigner" → openfermion.transforms.jordan_wigner

• "bravyi-kitaev" → openfermion.transforms.bravyi_kitaev

• "bravyi-kitaev-tree" → openfermion.transforms.bravyi_kitaev_tree

Examples

>>> from qdk_chemistry.algorithms import create
>>> from qdk_chemistry.data import MajoranaMapping
>>> mapper = create("qubit_mapper", "openfermion")
>>> mapping = MajoranaMapping.jordan_wigner(num_modes=n_spin_orbitals)
>>> qh = mapper.run(hamiltonian, mapping)

__init__()

Initialize OpenFermionQubitMapper.

name()

Return the algorithm name openfermion.

Return type:

str

class qdk_chemistry.plugins.openfermion.qubit_mapper.OpenFermionQubitMapperSettings

Bases: QubitMapperSettings

Settings configuration for an OpenFermionQubitMapper.

__init__()

Initialize OpenFermionQubitMapperSettings.