Feat: Added Verstraete-Cirac fermion-to-qubit encoding (#482)#515
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luffy-orf wants to merge 3 commits into
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Feat: Added Verstraete-Cirac fermion-to-qubit encoding (#482)#515luffy-orf wants to merge 3 commits into
luffy-orf wants to merge 3 commits into
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Pull request overview
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Adds Verstraete–Cirac (auxiliary-qubit) fermion-to-qubit encoding support, including stabilizer exposure/serialization and a generic mapper-side stabilizer penalty to recover the physical (codespace) spectrum.
Changes:
- Implement
MajoranaMapping::verstraete_cirac(LatticeGraph)and expose it (plusstabilizers) to Python via pybind11. - Add generic stabilizer penalty injection in the mapping engine and extend JSON serialization to persist stabilizers (and explicit qubit count for bilinear-only mappings).
- Add documentation + references and Python tests covering spectrum/locality/round-trips.
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
| python/tests/test_verstraete_cirac.py | New acceptance tests for VC factory, mapper integration, spectrum match, locality, and serialization round-trips. |
| python/src/pybind11/data/majorana_mapping.cpp | Exposes stabilizers and the verstraete_cirac factory to Python. |
| docs/source/user/comprehensive/algorithms/qubit_mapper.rst | Documents Verstraete–Cirac encoding and its stabilizer penalty behavior. |
| docs/source/references.bib | Adds VC-related citations. |
| cpp/src/qdk/chemistry/data/majorana_mapping_factories.cpp | Implements VC factory and stabilizer construction. |
| cpp/src/qdk/chemistry/data/majorana_mapping.cpp | Adds stabilizers storage + JSON persistence; adjusts without_tapering() and summary. |
| cpp/src/qdk/chemistry/data/majorana_map_engine.cpp | Adds generic stabilizer penalty term merging into the mapped Hamiltonian. |
| cpp/include/qdk/chemistry/data/majorana_mapping.hpp | Adds stabilizers() API and verstraete_cirac() factory declaration/docs. |
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| with tempfile.NamedTemporaryFile(suffix=".h5") as f: | ||
| with h5py.File(f.name, "w") as hf: | ||
| mapping.to_hdf5(hf) | ||
| with h5py.File(f.name, "r") as hf: | ||
| reloaded = MajoranaMapping.from_hdf5(hf) |
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| std::unordered_map<SparsePauliWord, std::complex<double>, SparsePauliWordHash> | ||
| merged; | ||
| merged.reserve(result.words.size() + stabilizers.size() + 1); | ||
| for (std::size_t i = 0; i < result.words.size(); ++i) { | ||
| merged[result.words[i]] += result.coefficients[i]; | ||
| } |
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| MajoranaMapResult penalized; | ||
| penalized.words.reserve(merged.size()); | ||
| penalized.coefficients.reserve(merged.size()); | ||
| for (auto& [word, coeff] : merged) { | ||
| if (protected_words.count(word) || std::abs(coeff) >= threshold) { | ||
| penalized.words.push_back(word); | ||
| penalized.coefficients.push_back(coeff); | ||
| } | ||
| } |
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| std::vector<std::pair<std::complex<double>, SparsePauliWord>> bilinears; | ||
| bilinears.reserve(M * (M - 1) / 2); | ||
| for (std::size_t J = 0; J < M; ++J) { | ||
| std::size_t p = J / 2, ap = J % 2; | ||
| std::size_t qp_qubit = 2 * sigma(p); | ||
| auto gamma_J = vc_jw_majorana(qp_qubit, ap == 0 ? op_x : op_y); | ||
| for (std::size_t K = J + 1; K < M; ++K) { | ||
| std::size_t q = K / 2, bq = K % 2; | ||
| std::size_t qq_qubit = 2 * sigma(q); | ||
| auto gamma_K = vc_jw_majorana(qq_qubit, bq == 0 ? op_x : op_y); | ||
|
|
||
| auto bare = PauliTermAccumulator::multiply_uncached(gamma_J, gamma_K); |
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Summary
Adds the Verstraete-Cirac (VC) locality-preserving fermion-to-qubit encoding as a
new
MajoranaMapping.verstraete_cirac(lattice)factory, consumable byQubitMapperwith no special-casing.
MajoranaMapping: introduces a generic, optionalstabilizers_member (a list of Pauli terms) with accessor + JSON/HDF5 serialization. No grid
metadata is stored on the data class.
verstraete_ciracrecovers latticecoordinates directly from a rectangular
LatticeGraph's adjacency, emits one VCblock per spin sector (
num_modes == 2 * n_sites,num_qubits == 4 * n_sites),and produces codespace stabilizers.
λ·(I − S)per stabilizeruniformly — no encoding-name checks, no grid logic — so non-redundant encodings
(Jordan-Wigner, etc.) are completely unaffected.
verstraete_ciracfactory and astabilizersaccessor.Test plan
New module
python/tests/test_verstraete_cirac.pycovering the acceptance criteria:QubitMapperconsumes eachwithout error; non-rectangular lattices are rejected.
match Jordan-Wigner to < 1e-10.
L in {2, 3, 4}.
Closes #482