Abstract

The microwave caesium atomic clock has formed an enduring basis for the SI second over the last few decades. The advent of laser cooling has underpinned the development of the cold caesium fountain clock, which demonstrates a frequency uncertainty of 1 part in 1015 per day. Since the turn of the century, the pace of research into alternative atomic clock technologies based on optical clocks has quickened considerably, to the extent that they now challenge the performance of the Cs fountain clock. This has been achieved in part by the arrival of the femtosecond comb which allows the high accuracy inter-relation between microwave and optical frequencies.

Optical clocks are based on state-of-the-art frequency-stabilised lasers probing very weak absorptions in a single cold trapped ion held in an electromagnetic trap or in an ensemble of cold atoms trapped within an optical lattice. This talk will aim to contrast the performance of trapped ion and optical lattice neutral atom clocks with the caesium fountain, discuss issues in remote high-accuracy clock comparison and point to future opportunities and applications.