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Bodine, Martha I.; Deschênes, Jean-Daniel; Khader, Isaac H.; Swann, William C.; Leopardi, Holly; Beloy, Kyle; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S.; Hume, David B.; Kedar, Dhruv; Kennedy, Colin J.; Koepke, Amanda; Leibrandt, David R.; Ludlow, Andrew D.; McGrew, William F.; Milner, William R.; Nicolodi, Daniele; Oelker, Eric; Parker, Thomas E.; Robinson, John M.; Romish, Stefania; Schäffer, Stefan A.; Sherman, Jeffrey A.; Sonderhouse, Lindsay; Yao, Jian; Ye, Jun; Zhang, Xiaogang; Newbury, Nathan R.; Sinclair, Laura C.
Physical review research, 09/2020, Volume: 2, Issue: 3Journal Article
We use frequency-comb-based optical two-way time-frequency transfer (O-TWTFT) to measure the optical frequency ratio of state-of-the-art ytterbium and strontium optical atomic clocks separated by a 1.5-km open-air link. Our free-space measurement is compared to a simultaneous measurement acquired via a noise-cancelled fiber link. Despite nonstationary, ps-level time-of-flight variations in the free-space link, ratio measurements obtained from the two links, averaged over 30.5 hours across six days, agree to 6×10^{−19}, showing that O-TWTFT can support free-space atomic clock comparisons below the 10^{−18} level.
