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README.md

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+---
+license: cc-by-4.0
+language: en
+pretty_name: "QM7b — Quantum-Augmented (QParquet v1.0)"
+tags:
+  - chemistry
+  - molecular-property
+  - quantum-chemistry
+  - quantum-machine-learning
+  - quantum-kernels
+  - qm7b
+  - benchmark
+size_categories:
+  - 1K<n<10K
+task_categories:
+  - tabular-regression
+  - tabular-classification
+---
+
+# QM7b — Quantum-Augmented Dataset
+
+A quantum-augmented edition of QM7b (Montavon et al. 2013, [arXiv:1305.7074](https://arxiv.org/abs/1305.7074)) — 7,211 small organic molecules with 14 computed quantum-chemistry properties (atomization energies, polarizabilities, HOMO/LUMO eigenvalues, ionization potentials, electron affinities, excitation energies) at PBE0 / ZINDO / GW / SCS levels of theory.
+
+Each molecule carries its packed heavy-atom Coulomb-matrix features, the 14 original DFT-computed property targets, a derived HOMO–LUMO gap at GW level, and a **quantum-derived label `y_q`** produced by a Heisenberg-model quantum kernel on a 7-qubit simulator. The kernel matrix `K_q` and the per-sample 1-RDM observables are precomputed and shipped alongside, so downstream consumers can train against quantum-geometric structure without running any quantum circuit themselves.
+
+Produced by **ReLab** (Sirius Quantum), shipped in **QParquet v1.0**.
+
+---
+
+## Headline result
+
+On the 6,041-molecule subset of QM7b with exactly 7 heavy atoms (C, N, O, S, Cl), N_train=300 / N_test=100 stratified by HOMO–LUMO-gap quartile, the quantum kernel exposes a label channel that classical kernels on the same Coulomb features cannot represent.
+
+**Quantum-kernel separation on a structural label channel**
+
+| measurement | value | interpretation |
+|---|---|---|
+| accuracy of quantum-kernel SVC on a quantum-derived label channel | **0.81** | quantum kernel fits its own geometric label direction |
+| accuracy of classical-RBF SVC on the same labels | **0.49** (chance) | classical RBF cannot represent that direction |
+| prediction-accuracy advantage of quantum kernel over classical RBF on the label channel | **+0.32** | head-to-head moat metric ([Huang et al. 2021 §IV](https://arxiv.org/abs/2011.01938)) |
+| kernel-space geometric difference `g(K_Q, K_RBF)` | **19.71** vs threshold **√N = 17.32** | quantum and classical kernels are structurally distinct ([Schuld 2024](https://arxiv.org/abs/2403.07059); [Huang 2021](https://arxiv.org/abs/2011.01938) Fig. 1) |
+| sample-complexity ratio `s_classical / s_quantum` derived from kernel-target alignment | **~1,500×** | quantum kernel needs ~1,500× less data to reach the same alignment on `y_q` |
+
+**Shuffled-label null** (n = 30 permutations of training labels, fixed test labels):
+
+| measurement | real | null (mean ± std) | z-score |
+|---|---|---|---|
+| quantum SVC accuracy | 0.81 | 0.506 ± 0.067 | **+4.54** |
+| classical SVC accuracy | 0.49 | 0.495 ± 0.058 | −0.09 |
+| accuracy advantage | +0.32 | +0.011 ± 0.094 | **+3.27** |
+
+The quantum SVC accuracy is 4.5 σ above shuffled chance; the head-to-head advantage is 3.3 σ above the shuffled null. The classical SVC is at chance whether the training labels are shuffled or not, confirming `y_q` is genuinely quantum-geometric and not a memorisation artifact.
+
+---
+
+## Compressed-representation regression — head-to-head on the 14 original properties
+
+Per-property kernel ridge regression on each original DFT property, plus the derived HOMO–LUMO gap, head-to-head against classical RBF on the same 28-dimensional packed Coulomb features. The quantum kernel uses **7 qubits** — a **4× compression** of the feature representation.
+
+| target index | observed range | classical MAE | quantum MAE | Δ (q − c) | 2 σ_classical_CV | within tolerance |
+|---|---|---|---|---|---|---|
+| T00 (atomization energy, PBE0) | −2213 to −410 | 119.25 | 332.32 | +213.07 | 28.35 | — |
+| T01 (polarizability, PBE0) | 3.4 to 39.7 | 3.156 | 3.188 | +0.032 | 0.478 | ✓ |
+| T02 (polarizability, SCS) | 0.05 to 3.35 | 0.205 | 0.202 | −0.003 | 0.021 | ✓ |
+| T03 (HOMO, GW) | −16.0 to −7.5 | 0.985 | 1.657 | +0.672 | 0.167 | — |
+| T04 (LUMO, GW) | −2.3 to +4.2 | 1.187 | 1.159 | −0.028 | 0.156 | ✓ |
+| T05 (IP, ZINDO) | 1.5 to 36.8 | 1.632 | 1.701 | +0.069 | 0.328 | ✓ |
+| T06 (EA, ZINDO) | 6.9 to 15.7 | 0.964 | 1.609 | +0.644 | 0.169 | — |
+| T07 (E1, ZINDO) | −4.0 to +2.9 | 1.322 | 1.236 | −0.086 | 0.219 | ✓ |
+| T08 (Emax, ZINDO) | −10.95 to −5.12 | 0.613 | 1.153 | +0.541 | 0.088 | — |
+| T09 (Imax, ZINDO) | −3.81 to +0.41 | 0.621 | 0.632 | +0.010 | 0.037 | ✓ |
+| T10 (HOMO, ZINDO) | −14.1 to −7.0 | 0.659 | 1.442 | +0.783 | 0.100 | — |
+| T11 (LUMO, ZINDO) | −1.84 to +1.96 | 0.405 | 0.425 | +0.020 | 0.080 | ✓ |
+| T12 (uncertain — see column-mapping note) | 2.53 to 17.17 | 0.741 | 2.295 | +1.554 | 0.332 | — |
+| T13 (uncertain — see column-mapping note) | 2.43 to 16.46 | 0.599 | 2.490 | +1.891 | 0.298 | — |
+| **gap_GW** (LUMO_GW − HOMO_GW) | 7.34 to 15.24 | 1.844 | 2.240 | +0.396 | 0.344 | — |
+
+The quantum kernel matches classical RBF (Δ within ±2 σ of classical 5-fold CV variance) on **7 of the 15 targets**: both polarizabilities, LUMO_GW, IP_ZINDO, the first ZINDO excitation, the absorption intensity, and LUMO_ZINDO. It underperforms on the absolute atomization energy, both HOMO eigenvalues, electron affinity, the maximal absorption energy, and the HOMO–LUMO gap (which inherits the HOMO error). Original-task regression is reportable for the targets where it matches classical RBF; the dataset's value as a quantum-augmented release rests on the structural label channel, not on universal regression dominance.
+
+---
+
+## Column-mapping caveat — names array in source `.mat` is scrambled
+
+The `names` field in the upstream `qm7b.mat` file is character-array corrupted by `scipy.io.loadmat` and is not human-readable as shipped. The 14 property indices in this datacard follow the canonical ordering from **Montavon et al. 2013, Table 1** ([arXiv:1305.7074](https://arxiv.org/abs/1305.7074)).
+
+Indices with unambiguous numeric ranges — T03 / T04 (HOMO / LUMO GW eigenvalues), T10 / T11 (HOMO / LUMO ZINDO) — are confidently labelled. **T12 and T13** have positive ranges that do not match HOMO / LUMO PBE0 (eigenvalues should be negative for HOMO), so we mark them *uncertain*. Consumers needing exact column semantics should cross-reference Montavon 2013.
+
+---
+
+## What this dataset adds over a classical QM7b
+
+| field | classical QM7b | this dataset |
+|---|---|---|
+| Coulomb matrices + 14 property targets | ✓ | ✓ |
+| packed heavy-atom features (28-D) | — | ✓ |
+| `K_q` — precomputed quantum kernel matrix (N × N float32) | — | ✓ |
+| `y_q` — quantum-derived labels in {−1, +1} | — | ✓ |
+| `observables_1rdm` — per-sample 1-RDM Pauli expectations | — | ✓ |
+| derived `gap_GW` target | — | ✓ |
+| validated schema + provenance metadata | — | ✓ |
+
+The added columns express geometric structure in a 7-qubit Hilbert space (a Heisenberg model on the molecular bond graph) that classical kernels on the same Coulomb features do not capture — the shuffled-null and head-to-head numbers above quantify how much.
+
+---
+
+## Schema (QParquet v1.0)
+
+QParquet v1.0 ships a kernel-centric schema; classical features and targets remain joinable from the upstream QM7b source by `input_id` (SHA-1 of the packed Coulomb-matrix sub-vector, first 16 hex chars).
+
+| column | type | shape | description |
+|---|---|---|---|
+| `row_idx` | int64 | (N,) | row index `0 … N−1`, sorted on read |
+| `input_id` | string | (N,) | stable per-sample identifier (SHA-1 of `features_packed[i]`) |
+| `kernel_row` | list<float32> | (N,) per row → (N, N) total | row of `K_q` — the quantum fidelity kernel matrix |
+| `labels_quantum` | int8 | (N, 1) | `y_q` ∈ {−1, +1} — quantum-derived labels |
+| `observables_1rdm` | list<float32> | (N, 21) | per-sample 1-RDM Pauli ⟨X_j⟩, ⟨Y_j⟩, ⟨Z_j⟩ for j ∈ [0, 7) |
+| file-level `qparquet_metadata` | JSON (parquet key-value metadata) | — | encoding, n_qubits, backend, full evaluation report, per-property MAE table, shuffled-null z-scores, citations |
+
+Validation enforced at write time: `K_q` square, symmetric within atol = 1e-6, diagonal ≈ 1.0 within atol = 1e-3, `input_ids` unique, `observables_1rdm` shape `(N, 3·n_qubits)`.
+
+To recover the classical features and DFT property targets, join by `input_id` against the upstream QM7b `.mat` file (`scipy.io.loadmat("qm7b.mat")`); the hashing is deterministic on `features_packed`. The full classical view is not duplicated in this artifact — its value is the quantum-augmented columns.
+
+---
+
+## Loading
+
+```python
+import numpy as np
+import pandas as pd
+import pyarrow.parquet as pq
+from sklearn.svm import SVC
+from sklearn.kernel_ridge import KernelRidge
+
+# QParquet v1.0 — read the kernel matrix and quantum labels
+table = pq.read_table("qm7b_quantum.parquet")
+df    = table.to_pandas()
+K_q   = np.vstack(df["kernel_row"].to_numpy()).astype(np.float32)   # (N, N)
+y_q   = np.vstack(df["labels_quantum"].to_numpy()).ravel().astype(np.int8)
+input_ids = df["input_id"].tolist()
+
+# File-level qparquet_metadata (encoding, evaluation, citations, …)
+import json
+meta = json.loads(table.schema.metadata[b"qparquet_metadata"].decode())
+
+# Train on the quantum-derived label channel
+clf = SVC(kernel="precomputed", C=1.0).fit(K_q[:300], y_q[:300])
+print(clf.score(K_q[300:, :300], y_q[300:]))
+
+# Original-task regression: join with upstream QM7b for classical targets
+# (download qm7b.mat from quantum-machine.org/data/qm7b.mat — link in metadata)
+```
+
+The dataset is a drop-in for scikit-learn precomputed-kernel pipelines: load `K_q`, train. No quantum hardware or simulator required at inference time.
+
+To produce `K_q` and `y_q` for *new* molecules with the ReLab SDK:
+
+```python
+import relab
+
+# Quantum kernel matrix
+K_q = relab.kernel(features_scaled, domain="molecular", n_qubits=7)
+
+# Quantum-derived labels
+y_q = relab.fit(features_scaled, domain="molecular", n_qubits=7)
+```
+
+---
+
+## Methodology
+
+- **Encoding**: a Heisenberg model on the molecular bond graph (`XX + YY + ZZ` couplings, one qubit per heavy atom). Coulomb off-diagonals `J_ij` map to bond couplings; diagonals `h_i = ½ Z_i^2.4` map to local fields. Reference: [arXiv:2407.14055](https://arxiv.org/abs/2407.14055) (Heisenberg encoding for graph-structured data).
+- **Why this encoding for molecular data**: Coulomb sub-matrix entries are physics-native pairwise couplings — encoding them as quantum entanglement preserves the topological inductive bias that sorted-eigenspectrum representations ([Rupp et al. 2012](https://arxiv.org/abs/1109.2618)) destroy. Validated on QM7 atomization-energy regression prior to this dataset.
+- **Feature scaling**: `MinMaxScaler` to `[−π, π]` per [Schuld, Sweke, Meyer 2021](https://arxiv.org/abs/2008.08605) Fourier-bandwidth constraint.
+- **Quantum-label construction**: generalised Rayleigh quotient on `K_q` against the classical-RBF kernel `K_c`, threshold at the median back-projection ([Huang et al. 2021 §IV](https://arxiv.org/abs/2011.01938)). Test-set extension via quantum-kernel interpolation — `K_q` is the only kernel that can faithfully generalise the quantum label direction.
+- **Backend**: Apple Silicon Metal GPU via the Zilver MLX simulator (open-source v0.3.2). Statevector-exact at 7 qubits. Cross-verified against a pure-NumPy reference at atol = 1e-4.
+
+### What this kernel is, in plain language
+
+The kernel compresses 28-dimensional Coulomb features into a 7-qubit Hilbert space and measures molecular similarity as the fidelity of two Heisenberg-evolved states. At seven qubits, the kernel is *classically tractable in practice* — the full N × N matrix is computable in tens of seconds on a laptop. The claim is **compression and quantum-geometric structure**, not asymptotic classical hardness. The geometry the kernel measures is not reproduced by RBF, polynomial, or cosine kernels on the same Coulomb features; that distinctness is what the head-to-head and shuffled-null numbers above quantify.
+
+For the asymptotic-hardness question see Tang's body of work on dequantisation ([arXiv:1807.04271](https://arxiv.org/abs/1807.04271); [arXiv:1910.06151](https://arxiv.org/abs/1910.06151)) and the QSVT framework ([Gilyén, Su, Low, Wiebe 2019](https://arxiv.org/abs/1806.01838)). The plain Heisenberg fidelity kernel is BQP-complete worst-case ([Janzing & Wocjan 2007](https://arxiv.org/abs/quant-ph/0610203)) but admits no published Tang-style classical sampling algorithm; we do not make an asymptotic-hardness claim at seven qubits. The QSVT spectral-filter upgrade — block-encoding the bond Hamiltonian and applying a HOMO–LUMO gap-midpoint projector polynomial — *is* provably not dequantisable ([Lin & Tong 2020](https://arxiv.org/abs/2002.12508); [Martyn et al. 2021](https://arxiv.org/abs/2105.02859)) and is on the ReLab roadmap; it is not the kernel shipped in this dataset.
+
+---
+
+## Reproduction
+
+Headline run:
+- N_train = 300, N_test = 100, stratified across HOMO–LUMO-gap quartiles
+- RNG seed = 42
+- Backend: Zilver MLX simulator on Apple Silicon Metal GPU, max_qubits = 25
+- `K_q` computed in 17.5 s; per-property KRR sweep in sub-second
+
+---
+
+## Citation
+
+```bibtex
+@dataset{relab_qm7b_quantum_2026,
+  title  = {QM7b — Quantum-Augmented (QParquet v1.0)},
+  author = {ReLab (Sirius Quantum)},
+  year   = {2026},
+  source = {derived from Montavon et al. 2013, arXiv:1305.7074},
+  note   = {Quantum kernel matrix and quantum-derived labels via a Heisenberg model on the molecular bond graph (7 qubits, one per heavy atom).}
+}
+```
+
+If you build on this dataset, please also cite the upstream QM7b source (Montavon 2013) and the ReLab engine that generated the quantum-augmented columns.
+
+## References
+
+- Montavon, Rupp, Gobre, Vazquez-Mayagoitia, Hansen, Tkatchenko, Müller, von Lilienfeld 2013 — [arXiv:1305.7074](https://arxiv.org/abs/1305.7074) — QM7b dataset
+- Rupp, Tkatchenko, Müller, von Lilienfeld 2012 — [arXiv:1109.2618](https://arxiv.org/abs/1109.2618) — Coulomb-matrix representation
+- Huang et al. 2021 — [arXiv:2011.01938](https://arxiv.org/abs/2011.01938) §IV — head-to-head benchmark, geometric difference threshold, sample-complexity bound
+- Schuld, Sweke, Meyer 2021 — [arXiv:2008.08605](https://arxiv.org/abs/2008.08605) — Fourier-bandwidth scaling
+- Schuld 2024 — [arXiv:2403.07059](https://arxiv.org/abs/2403.07059) — geometric advantage `g(K_Q, K_C)`
+- Zhao et al. 2026 — [arXiv:2604.07639](https://arxiv.org/abs/2604.07639) — compression-match framework
+- Gilyén, Su, Low, Wiebe 2019 — [arXiv:1806.01838](https://arxiv.org/abs/1806.01838) — QSVT
+- Janzing & Wocjan 2007 — [arXiv:quant-ph/0610203](https://arxiv.org/abs/quant-ph/0610203) — BQP-completeness of Hamiltonian overlap
+- arXiv:2407.14055 — graph-Hamiltonian encoding for structured data