Test of special relativity using a fiber network of optical clocks. Hunting for topological dark matter with atomic clocks. Synchronization of clocks through 12 km of strongly turbulent air over a city. Synchronization of distant optical clocks at the femtosecond level. Atomic clock performance enabling geodesy below the centimetre level.
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Towards the optical second: verifying optical clocks at the SI limit. Towards a redefinition of the second based on optical atomic clocks. The CIPM list of recommended frequency standard values: guidelines and procedures. A clock network for geodesy and fundamental science. The technique we report can not only be directly used in ground-based applications, but could also lay the groundwork for future satellite time–frequency dissemination. We observe that the stability we have reached is retained for channel losses up to 89 dB. Key technologies essential to this achievement include the deployment of high-power frequency combs, high-stability and high-efficiency optical transceiver systems and efficient linear optical sampling. Here we report time–frequency dissemination with an offset of 6.3 × 10 −20 ± 3.4 × 10 −19 and an instability of less than 4 × 10 −19 at 10,000 s through a free-space link of 113 km. However, previous attempts at free-space dissemination of time and frequency at high precision did not extend beyond dozens of kilometres 10, 11. As the frequency instability for state-of-the-art optical clocks has reached the 10 −19 level 8, 9, the vision of a global-scale optical network that achieves comparable performances requires the dissemination of time and frequency over a long-distance free-space link with a similar instability of 10 −19. Networks of optical clocks find applications in precise navigation 1, 2, in efforts to redefine the fundamental unit of the ‘second’ 3, 4, 5, 6 and in gravitational tests 7. Nature volume 610, pages 661–666 ( 2022) Cite this article Free-space dissemination of time and frequency with 10 −19 instability over 113 km
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