{
  "abstract": "We develop an effective thermodynamics for a qubit whose energy gap depends inversely on a volume-like control parameter, $Δ(V)=Δ_0/V$, where $V$ is a spectral-control coordinate rather than a literal mechanical volume. Starting from the canonical Gibbs state, we derive a complete thermodynamic structure from the Helmholtz potential and its Legendre and stability properties, including the fundamental relation $S(U,V)$, a generalized pressure conjugate to $V$, the equation of state $U=PV$, the first law, and the associated Maxwell relations. Reversible adiabats preserve the Gibbs populations and satisfy $TV=\\mathrm{const.}$ and $PV^2=\\mathrm{const.}$, corresponding to an effective exponent $γ=2$. The resulting effective Carnot cycle attains the Carnot efficiency, $η_{\\mathrm{Carnot}}=1-T_C/T_H$, whereas the Otto cycle yields $η_{\\mathrm{Otto}}=1-V_{\\min}/V_{\\max}$ and remains strictly sub-Carnot at finite work output. We identify the source of Otto irreversibility exactly: entropy is produced entirely during the isochoric thermalizations, and the cycle entropy production quantifies the informational mismatch between the adiabatically transported states and the reservoir-selected Gibbs states through the sum of the corresponding quantum relative entropies. Finally, we show that unitary-generated nonpassivity can act as a nonequilibrium battery, producing an apparent efficiency above Carnot when its preparation cost is omitted. At the same time, complete work accounting restores the thermodynamic bound.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.08040",
  "author_total": 2,
  "authors": [
    {
      "name": "André T. Cesário"
    },
    {
      "name": "Marcela Herrera"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/bq2m4nmhmffmc.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.08040",
  "fulltext_url": null,
  "id": "bq2m4nmhmffmc",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.08040",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "quant-ph"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.08040",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-05",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/bq2m4nmhmffmc.ris",
  "sources": [
    {
      "first_seen": "2026-11-06T18:21:30Z",
      "native_id": "2611.08040",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.08040"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:quant-ph",
      "subfield": "quantum"
    }
  ],
  "title": "Effective Thermodynamics of a Volume-Dependent Qubit",
  "title_text": "Effective Thermodynamics of a Volume-Dependent Qubit",
  "type": "preprint",
  "updated_at": "2026-11-06T18:21:30Z",
  "url": "https://research.draconitic.com/paper/bq2m4nmhmffmc",
  "venue": "arXiv",
  "versions": []
}