{
  "abstract": "Sample-based quantum diagonalization (SQD) accuracy remains limited for strongly correlated systems like iron-sulfur clusters. This accuracy heavily depends on the mean-field reference state, which determines the sampling ansatz and configuration-recovery target. We extend the qcsc-prefect workflow to support a broken-symmetry unrestricted Hartree-Fock (BS-UHF) starting point, derived from atom-localized antiferromagnetic initial guesses. For the $[Fe_4S_4(SCH_3)_4]^{2-}$ cubane (54 electrons, 36 orbitals, 72 data qubits; 88 total qubits), this lowers the mean-field reference by $\\approx 534$ mHa relative to the Restricted Hartree-Fock (RHF) solution (-327.0809 vs. -326.5474 Ha). Combined with deep multi-step configuration recovery on ROQUO GPU nodes at subspace dimension $d = 3 \\times 10^{10}$, we reach $E = -327.235076$ Ha. This is 4.3 mHa above the finite-$D = 4000$ DMRG value (-327.2393952 Ha) and $\\sim 512-517$ mHa below a previous same-active-space RHF-reference SQD calculation. Extrapolating to the $d \\to \\infty$ limit via a Gaussian-in-log $d$ fitting ansatz gives an asymptotic estimate $E_\\infty = -327.244468$ Ha $\\pm 1.05$ mHa, just 0.33 mHa above our discarded-weight-extrapolated DMRG estimate ($E_{D\\to\\infty} = -327.244797$ Ha $\\pm 0.46$ mHa), well within their combined $1σ$ uncertainty. We characterize the determinant-subspace composition driving convergence, show matching validation on $[Fe_2S_2(SCH_3)_4]^{2-}$, and report multi-HPC execution on Fugaku, Miyabi-G, and ROQUO. We conclude that reference-state preparation, rather than subspace size alone, is a key driver of SQD energy accuracy under strong electronic correlation.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.04496",
  "author_total": 10,
  "authors": [
    {
      "name": "Kunal Kumar"
    },
    {
      "name": "Tomonori Shirakawa"
    },
    {
      "name": "Boseong Kim"
    },
    {
      "name": "Ryo Wakizaka"
    },
    {
      "name": "Ikko Hamamura"
    },
    {
      "name": "Mitsuhisa Sato"
    },
    {
      "name": "Seiji Yunoki"
    },
    {
      "name": "Mario Motta"
    },
    {
      "name": "Hiroshi Horii"
    },
    {
      "name": "Yuri Kobayashi"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/bgtdy2frhcw40.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.04496",
  "fulltext_url": null,
  "id": "bgtdy2frhcw40",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.04496",
  "language": null,
  "licence": "CC-BY-NC-ND-4.0",
  "licence_label": "CC BY-NC-ND 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.chem-ph"
    ],
    [
      "arxiv",
      "quant-ph"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.04496",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/bgtdy2frhcw40.ris",
  "sources": [
    {
      "first_seen": "2026-11-04T15:21:25Z",
      "native_id": "2611.04496",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.04496"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "arxiv:physics.chem-ph",
      "subfield": "physical"
    },
    {
      "field": "physics",
      "origin": "arxiv:quant-ph",
      "subfield": "quantum"
    }
  ],
  "title": "Broken-Symmetry Reference States for Sample-Based Quantum Diagonalization with Near-DMRG Accuracy",
  "title_text": "Broken-Symmetry Reference States for Sample-Based Quantum Diagonalization with Near-DMRG Accuracy",
  "type": "preprint",
  "updated_at": "2026-11-06T18:21:01Z",
  "url": "https://research.draconitic.com/paper/bgtdy2frhcw40",
  "venue": "arXiv",
  "versions": []
}