@article{11881,
  author = {Eric Oelker and Ross Hutson and C. Kennedy and Lindsay Sonderhouse and Tobias Bothwell and Akihisa Goban and Dhruv Kedar and Christian Sanner and J. Robinson and Edward Marti and Dan-Gheorghita Matei and Thomas Legero and M. Giunta and Ronald Holzwarth and Fritz Riehle and Uwe Sterr and Jun Ye},
  title = {Demonstration of 4.8 x 10^(-17) stability at 1s for two independent optical clocks},
  abstract = {Optical atomic clocks require local oscillators with exceptional optical coherence owing to the challenge of performing spectroscopy on their ultranarrow-linewidth clock transitions. Advances in laser stabilization have thus enabled rapid progress in clock precision. A new class of ultrastable lasers based on cryogenic silicon reference cavities has recently demonstrated the longest optical coherence times to date. Here we utilize such a local oscillator with two strontium (Sr) optical lattice clocks to achieve an advance in clock stability. Through an anti-synchronous comparison, the fractional instability of both clocks is assessed to be 4.8x10<sup>-17</sup>/√τ for an averaging time τ(in seconds). Synchronous interrogation enables each clock to average at a rate of 3.5x10<sup>-17</sup>/√τ, dominated by quantum projection noise, and reach an instability of 6.6 x 10<sup>-19</sup> over an hour-long measurement. The ability to resolve sub-10<sup>-18</sup>-level frequency shifts in such short timescales will affect a wide range of applications for clocks in quantum sensing and fundamental physics.},
  year = {2019},
  journal = {Nature Photonics},
  volume = {13},
  pages = {714–719},
  month = {2019-07},
  issn = {1749-4885},
  url = {https://www.nature.com/articles/s41566-019-0493-4$\#$Abs1},
  doi = {10.1038/s41566-019-0493-4},
}