Demonstration of a mobile optical clock ensemble at sea

Atomic clocks are at the leading edge of accuracy and precision and are essential for synchronisation of distributed critical infrastructure, position, navigation and timing, and scientific applications. There has been significant improvements in the performance of atomic clocks with the shift from microwave to optical frequency transitions. However, this performance increase has come at the cost of size, complexity and fragility, which has confined optical clocks to laboratories. Here we report on a recent international collaboration where three emerging optical clocks, each based on different operating principles, were trialled at sea. These clocks demonstrated world-class performance and reliability by providing stable frequency outputs in optical, microwave and radio-frequency domains over three weeks of unsupervised naval operation.