{
  "annotation_id": "083fd64a-d1d6-4f86-81f1-2447886caea8",
  "date_created": "2026-03-02T18:00:32.940000Z",
  "date_modified": "2026-03-02T18:00:32.940000Z",
  "file_hash": "80cbc46e983ac65b2b081dc66ee4b90c498b0012f2e75c963d062f0e2864718e",
  "private": false,
  "record": {
    "abstract": "The frequency comb created by a femtosecond mode-locked laser and a\nmicrostructured fiber is used to phase coherently measure the frequencies of\nboth the Hg^+ and Ca optical standards with respect to the SI second as\nrealized at NIST. We find the transition frequencies to be f_Hg=1 064 721 609\n899 143(10) Hz and f_Ca=455 986 240 494 158(26) Hz, respectively. In addition\nto the unprecedented precision demonstrated here, this work is the precursor to\nall-optical atomic clocks based on the Hg^+ and Ca standards. Furthermore, when\ncombined with previous measurements, we find no time variations of these atomic\nfrequencies within the uncertainties of |(df_Ca/dt)/f_Ca| \u003c 8 x 10^{-14}\nyr^{-1}, and |(df_Hg/dt)/f_Hg|\u003c 30 x 10^{-14} yr^{-1}.",
    "arxiv_id": "physics/0101029",
    "authors": [
      "Th. Udem",
      "S. A. Diddams",
      "K. R. Vogel",
      "C. W. Oates",
      "E. A. Curtis",
      "W. D. Lee",
      "W. M. Itano",
      "R. E. Drullinger",
      "J. C. Bergquist",
      "L. Hollberg"
    ],
    "categories": [
      "physics.atom-ph",
      "physics.optics"
    ],
    "doi": "10.1103/PhysRevLett.86.4996",
    "title": "Absolute Frequency Measurements of the Hg^+ and Ca Optical Clock   Transitions with a Femtosecond Laser",
    "url": "https://arxiv.org/abs/physics/0101029"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "30030df0-5ca2-424b-bdc9-83da87e9348f",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}