Optical to microwave clock frequency ratios with a nearly continuous   strontium optical lattice clock
  Optical lattice clocks are at the forefront of frequency metrology. Both the instability and systematic uncertainty of these clocks have been reported to be two orders of magnitude smaller than the best microwave clocks. For this reason, a redefinition of the SI second based on optical clocks seems possible in the near future. However, the operation of optical lattice clocks has not yet reached the reliability that microwave clocks have achieved so far. In this paper, we report on the operation of a strontium optical lattice clock that spans several weeks, with more than 80% uptime. We make use of this long integration time to demonstrate a reproducible measurement of frequency ratios between the strontium clock transition and microwave Cs primary and Rb secondary frequency standards. 
J\'er\^ome Lodewyck, S{\l}awomir Bilicki, Eva Bookjans, Jean-Luc   Robyr, Chunyan Shi, Gr\'egoire Vallet, Rodolphe Le Targat...
physics.atom-ph