{
  "id": "2409.09139",
  "version": "v1",
  "published": "2024-09-13T18:47:56.000Z",
  "updated": "2024-09-13T18:47:56.000Z",
  "title": "Conservation of angular momentum on a single-photon level",
  "authors": [
    "Lea Kopf",
    "Rafael Barros",
    "Shashi Prabhakar",
    "Enno Giese",
    "Robert Fickler"
  ],
  "categories": [
    "quant-ph"
  ],
  "abstract": "Identifying conservation laws is central to every subfield of physics, as they illuminate the underlying symmetries and fundamental principles. These laws have far-reaching implications, not only enhancing our theoretical understanding but also enabling practical applications. A prime example can be found in quantum optics: The conservation of orbital angular momentum (OAM) during spontaneous parametric down-conversion (SPDC) enables the generation of a photon pair with entangled OAM. This quantum correlation is commonly attributed to the conservation of the topological charge of a strong coherent pump field driving the process. However, the topological charge of such a classical field only determines the average OAM per photon, so that the total OAM carried by the field has fluctuations as a direct consequence of its photon statistics. In this article, we report on the first realisation of SPDC pumped by a single twisted photon. Our results confirm OAM conservation at the single-photon level and directly transfer to SPDC induced by classical pump fields by averaging over their photon statistics. In addition to verifying a central property of SPDC, our results present the first implementation of cascaded down-conversion in bulk media, setting the stage for experiments on the direct generation of multi-photon high-dimensional entanglement using all degrees of freedom of light.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-09-13T18:47:56.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "single-photon level",
      "angular momentum",
      "photon statistics",
      "results confirm oam conservation",
      "strong coherent pump field driving"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}