{
  "abstract": "In molecular variational quantum eigensolver (VQE) calculations for a fixed electron-number sector, the projected-sector energy alone does not certify that a prepared state is physically valid. We show that a state can have zero projected-sector error while almost all of its probability mass lies outside the target particle-number sector. We therefore evaluate ansatz families using three quantities: projected-sector error, leakage outside the physical sector and parameter count. Our noiseless experiments show that particle-preserving UCC-style families eliminate leakage induced by ansatze, but do not guarantee ground-state accuracy. In the parameter-budget comparison experiments, the one-shot ranking rules select identical generator sequences and yield identical errors. The adaptive hybrid procedure achieves lower mean projected-sector errors at selected budgets. Using established Kraus invariant-subspace criteria, we also express channel-induced leakage through a positive operator and discuss global and local depolarizing noise analytically. This gives a practical diagnostic framework for comparing ansatze beyond energy alone.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.13521",
  "author_total": 1,
  "authors": [
    {
      "name": "Yuan-Chieh Chen"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/68v45ptqdy5kf.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.13521",
  "fulltext_url": null,
  "id": "68v45ptqdy5kf",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.13521",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "quant-ph"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.13521",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-11",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/68v45ptqdy5kf.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.13521",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.13521"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:quant-ph",
      "subfield": "quantum"
    }
  ],
  "title": "Energy Is Not Enough: Leakage-Aware Ansatz Criterion for Variational Quantum Eigensolvers",
  "title_text": "Energy Is Not Enough: Leakage-Aware Ansatz Criterion for Variational Quantum Eigensolvers",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/68v45ptqdy5kf",
  "venue": "arXiv",
  "versions": []
}