![]() Ultrastable optical clock with two cold-atom ensembles. Advanced satellite-based frequency transfer at the 10 −16 level. Comparison between frequency standards in europe and the usa at the 10 −15 uncertainty level. Wave-front temporal spectra in high-resolution imaging through turbulence. (ed.) Laser Beam Propagation in the Atmosphere Topics in Applied Physics Vol. Measurement of the impact of turbulence anisoplanatism on precision free-space optical time transfer. Impact of turbulence on high-precision ground-satellite frequency transfer with two-way coherent optical links. Time and laser ranging: a window of opportunity for geodesy, navigation, and metrology. I-SOC Scientific Requirements Technical Report (European Space Research and Technology Centre, 2017).Įxertier, P. Time transfer by laser link: a complete analysis of the uncertainty budget. Ultrastable free-space laser links for a global network of optical atomic clocks. Comparing optical oscillators across the air to milliradians in phase and 10 −17 in frequency. ![]() Femtosecond time synchronization of optical clocks off of a flying quadcopter. Frequency ratio measurements at 18-digit accuracy using an optical clock network. Optical atomic clock comparison through turbulent air. Experimental simulation of time and frequency transfer via an optical satellite-ground link at 10 -18 instability. Optical time-frequency transfer across a free-space, three-node network. Optical two-way time and frequency transfer over free space. Optical lattice clocks and quantum metrology. ![]() An accurate and robust metrological network for coherent optical frequency dissemination. A 920-kilometer optical fiber link for frequency metrology at the 19th decimal place. Optical-frequency transfer over a single-span 1840 km fiber link. Experimental twin-field quantum key distribution through sending or not sending. Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks. Ultracold molecules: new probes on the variation of fundamental constants. Search for new physics with atoms and molecules. 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. A fermi-degenerate three-dimensional optical lattice clock. Gravitational wave detection with optical lattice atomic clocks. The unit of time: present and future directions. 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. Free-space dissemination of time and frequency with 10 −19 instability over 113 km
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