{
  "annotation_id": "3d3cca9b-e4b8-45ea-ba72-46c55905d409",
  "date_created": "2026-03-02T18:02:06.935000Z",
  "date_modified": "2026-03-02T18:02:06.935000Z",
  "file_hash": "0734ebf8a3bcbdc16e1b15810f8bdafd64fe84ac80afe2d3091554b82d2cdcf1",
  "private": false,
  "record": {
    "abstract": "We study macroscopic entanglement of various pure states of a one-dimensional\nN-spin system with N\u003e\u003e1. Here, a quantum state is said to be macroscopically\nentangled if it is a superposition of macroscopically distinct states. To judge\nwhether such superposition is hidden in a general state, we use an essentially\nunique index p: A pure state is macroscopically entangled if p=2, whereas it\nmay be entangled but not macroscopically if p\u003c2. This index is directly related\nto the stability of the state. We calculate the index p for various states in\nwhich magnons are excited with various densities and wavenumbers. We find\nmacroscopically entangled states (p=2) as well as states with p=1. The former\nstates are unstable in the sense that they are unstable against some local\nmeasurements. On the other hand, the latter states are stable in the senses\nthat they are stable against local measurements and that their decoherence\nrates never exceed O(N) in any weak classical noises. For comparison, we also\ncalculate the von Neumann entropy S(N) of a subsystem composed of N/2 spins as\na measure of bipartite entanglement. We find that S(N) of some states with p=1\nis of the same order of magnitude as the maximum value N/2. On the other hand,\nS(N) of the macroscopically entangled states with p=2 is as small as O(log N)\u003c\u003c\nN/2. Therefore, larger S(N) does not mean more instability. We also point out\nthat these results are analogous to those for interacting many bosons.\nFurthermore, the origin of the huge entanglement, as measured either by p or\nS(N), is discussed to be due to the spatial propagation of magnons.",
    "arxiv_id": "quant-ph/0405173",
    "authors": [
      "Tomoyuki Morimae",
      "Ayumu Sugita",
      "Akira Shimizu"
    ],
    "categories": [
      "quant-ph",
      "cond-mat.stat-mech"
    ],
    "doi": "10.1103/PhysRevA.71.032317",
    "journal_ref": "Phys. Rev. A 71, 032317 (2005)",
    "title": "Macroscopic entanglement of many-magnon states",
    "url": "https://arxiv.org/abs/quant-ph/0405173"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "9d48d4bb-7b83-45ab-9e22-728199b4ed57",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}