{
  "abstract": "Photons are mutually nearly noninteracting particles, so thermalized photon ensembles are commonly obtained not from direct particle-particle-interactions but rather from contact with matter, which can constitute a reservoir for the photon gas. We develop a theory model for photons in a material-filled (e.g. liquid dye) optical microcavity, with the aim to study the fluctuation properties using a free-energy description for noninteracting photons coupled to a reservoir of material electronic excitations. To begin with, we use a single mode description for the condensate. For a small relative size of the material reservoir, corresponding to the canonical regime, condensate number fluctuations are small, and the derived free energy landscape takes the usual Mexican-hat shaped form such that spontaneous symmetry breaking occurs. In contrast, for a large relative size of the reservoir, corresponding to the grand canonical regime, fluctuations become as large as the average particle number. We show that the resulting free energy landscape acquires a bowl-shaped form, with a single minimum at the origin. Thus, a macroscopic occupation of the ground state (i.e., Bose-Einstein condensation) in the absence of spontaneous symmetry breaking is expected. We also provide a model for the treatment of a photon gas trapped in a box-shaped potential with spatially distributed coupling to a reservoir. The model predicts, for example, a statistically fluctuating pattern of islands with long-range coherence, resembling transient microcondensates.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.05287",
  "author_total": 7,
  "authors": [
    {
      "name": "Martin Weitz"
    },
    {
      "name": "Andreas Redmann"
    },
    {
      "name": "Riccardo Panico"
    },
    {
      "name": "Leon Kleeblank"
    },
    {
      "name": "Kevin J. H. Peters"
    },
    {
      "name": "Frank Vewinger"
    },
    {
      "name": "Julian Schmitt"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/c3h8pff5rvzyb.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.05287",
  "fulltext_url": null,
  "id": "c3h8pff5rvzyb",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.05287",
  "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"
    ],
    [
      "openalex",
      "3107|Strong Light-Matter Interactions"
    ]
  ],
  "openalex": "W7211889688",
  "pdf_url": "https://arxiv.org/pdf/2609.05287",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-04",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/c3h8pff5rvzyb.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:19:14Z",
      "native_id": "2609.05287",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.05287"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.quant-gas",
      "subfield": "amo"
    },
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.quant-gas",
      "subfield": "condensed-matter"
    }
  ],
  "title": "Fluctuations of a Photon Bose-Einstein Condensate Coupled to a Reservoir: Describing Coherence Properties in a Free-Energy Model",
  "title_text": "Fluctuations of a Photon Bose-Einstein Condensate Coupled to a Reservoir: Describing Coherence Properties in a Free-Energy Model",
  "type": "preprint",
  "updated_at": "2026-10-30T12:19:14Z",
  "url": "https://research.draconitic.com/paper/c3h8pff5rvzyb",
  "venue": "arXiv",
  "versions": []
}