Optical clocks at sea.

Deployed optical clocks will improve positioning for navigational autonomy, provide remote time standards for geophysical monitoring and distributed coherent sensing, allow time synchronization of remote quantum networks and provide operational redundancy for national time standards. Although laboratory optical clocks now reach fractional inaccuracies below 10 (refs. ), transportable versions of these high-performing clocks have limited utility because of their size, environmental sensitivity and cost.