{
  "annotation_id": "6d848722-3475-4f87-bc02-9883e033f016",
  "date_created": "2026-03-02T18:02:03.667000Z",
  "date_modified": "2026-03-02T18:02:03.667000Z",
  "file_hash": "bceb748bb8708063a96e09d29c466d95aecaea174675faef323e970d400dd140",
  "private": false,
  "record": {
    "abstract": "We study the physics of four-photon states generated in spontaneous\nparametric down-conversion with a pulsed pump field. In the limit where the\ncoherence time of the photons t_c is much shorter than the duration of the pump\npulse Delta t, the four photons can be described as two independent pairs. In\nthe opposite limit, the four photons are in a four-particle entangled state.\nAny intermediate case can be characterized by a single parameter chi, which is\na function of t_c/Delta t. We present a direct measurement of chi through a\nsimple experimental setup. The full theoretical analysis is also provided.",
    "arxiv_id": "quant-ph/0310167",
    "authors": [
      "Hugues de Riedmatten",
      "Valerio Scarani",
      "Ivan Marcikic",
      "Antonio Acin",
      "Wolfgang Tittel",
      "Hugo Zbinden",
      "Nicolas Gisin"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1080/09500340408232478",
    "journal_ref": "J.Mod.Opt. 51, 1637 (2004)",
    "title": "Two independent photon pairs versus four-photon entangled states in   parametric down conversion",
    "url": "https://arxiv.org/abs/quant-ph/0310167"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "61a52e88-be7d-4042-981c-55688826bfd8",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}