{
  "abstract": "Bose-Einstein condensation in the grand canonical ensemble admits a formulation in terms of a phase-density decomposition of the condensate mode operator $\\hatψ_{\\bf 0}$. In the presence of macroscopic condensate number fluctuations this representation presents nontrivial implications. In particular, we show that, for the ideal gas, under the assumption of a well-defined phase and a fluctuating condensate density, the square modulus of the anomalous average $\\langle \\hatψ_{\\bf 0}\\rangle$ can provide only a fraction of the whole condensate density $ρ_{\\bf 0}$ and for the grand canonical statistics of the ideal Bose gas one obtains the value $|\\langle {\\hat ψ}_{\\bf 0}\\rangle|^2 =(π/4) ρ_{\\bf 0}$. The remaining part is supplemented by the (macroscopic) fluctuations of $\\hatψ_{\\bf 0}$, which become a distinctive feature of the BEC in this setting. This provides a transparent physical picture of a condensate of photons with a well-defined phase but large number fluctuations, as observed in dye-filled microcavity photon experiments. We also propose a way to access the square modulus of the anomalous average to test theoretical predictions.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: Phys. Rev. A 114, 043704, 2026",
  "arxiv": "2607.12926",
  "author_total": 4,
  "authors": [
    {
      "name": "L. Salasnich"
    },
    {
      "name": "A. Crisanti"
    },
    {
      "name": "A. Sarracino"
    },
    {
      "name": "M. Zannetti"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/240g8220a520y.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2607.12926",
  "fulltext_url": null,
  "id": "240g8220a520y",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2607.12926",
  "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",
      "cond-mat.quant-gas"
    ],
    [
      "arxiv",
      "cond-mat.stat-mech"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2607.12926",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-05",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/240g8220a520y.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:01Z",
      "native_id": "2607.12926",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2607.12926"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.quant-gas",
      "subfield": "amo"
    },
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.quant-gas",
      "subfield": "condensed-matter"
    },
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.stat-mech",
      "subfield": "statistical-nonlinear"
    }
  ],
  "title": "Coherent Bose-Einstein condensation with fluctuating density",
  "title_text": "Coherent Bose-Einstein condensation with fluctuating density",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:01Z",
  "url": "https://research.draconitic.com/paper/240g8220a520y",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1103/lwc2-1kdp",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}