Optical clock intercomparison with $6\times 10^{19}$ precision in one hour
Abstract
Improvements in atomlight coherence are foundational to progress in quantum information science, quantum optics, and precision metrology. Optical atomic clocks require local oscillators with exceptional optical coherence due 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. In this work we utilize such a local oscillator, along with a stateoftheart frequency comb for coherence transfer, with two Sr optical lattice clocks to achieve an unprecedented level of clock stability. Through an antisynchronous comparison, the fractional instability of both clocks is assessed to be $4.8\times 10^{17}/\sqrt{\tau}$ for an averaging time $\tau$ in seconds. Synchronous interrogation reveals a quantum projection noise dominated instability of $3.5(2)\times10^{17}/\sqrt{\tau}$, resulting in a precision of $5.8(3)\times 10^{19}$ after a single hour of averaging. The ability to measure sub$10^{18}$ level frequency shifts in such short timescales will impact a wide range of applications for clocks in quantum sensing and fundamental physics. For example, this precision allows one to resolve the gravitational red shift from a 1 cm elevation change in only 20 minutes.
 Publication:

arXiv eprints
 Pub Date:
 February 2019
 arXiv:
 arXiv:1902.02741
 Bibcode:
 2019arXiv190202741O
 Keywords:

 Physics  Atomic Physics;
 Quantum Physics
 EPrint:
 Nature Photonics 13, 714719 (2019)