La Rivista del Nuovo Cimento

## Optical atomic clocks

Authors: N. Poli, C. W. Oates, P. Gill, G. M. Tino
DOI: 10.1393/ncr/i2013-10095-x
pp. 555-624
Published online 11 December 2013
Abstract: In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femtosecond optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today's best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in $10^{18}$. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.