Coherent optical clock down-conversion for microwave frequencies with 10-18 instability.
Nakamura T, Davila-Rodriguez J, Leopardi H, Sherman JA, Fortier TM, Xie X, Campbell JC, McGrew WF, Zhang X, Hassan YS, Nicolodi D, Beloy K, Ludlow AD, Diddams SA, Quinlan F. Coherent optical clock down-conversion for microwave frequencies with 10-18 instability. Science. 2020 05 22; 368(6493):889-892.