Abstract

Atomic clocks are used constantly in daily life from synchronising computer networks to GPS navigation, and after the redefinition of the SI units in November 2018 accuratemeasurement of any physical quantity will be dependant on our ability to make accurate clocks.
Based on the use of ultra-stable lasers to measure the electron structure of individual atoms, optical atomic clocks  are the most accurate measurement devices ever created - up to 100 times more accurate than the microwave caesium fountain clock that currently defines the second - reaching fractional uncertainties of 1 part in 10 ^{^18} .  This accuracy is equivalent to counting the amount of sand on all the beaches in the world, and getting the correct answer to within a single grain, or keeping time accurate to one second in the lifetime of the universe. However atomic clocks are not only useful for defining measurement units; as tools for studying atomic structure they can also be used for testing Quantum Mechanics and General Relativity, probing for physics beyond what we currently understand.  Clocks around the world are hunting for dark matter, testing the Einstein Equivalence Principle and searching to see if the fundamental 'constants' of nature live up to their name.
In this talk I hope to provide an overview of current research into optical atomic clocks: the systematic shifts and environmentalperturbations which limit their accuracy and stability, how this leads to the wide variety of atomic species under investigation, how we verify that they are accurate, and finally how people are trying to use them for both real-world applications and as sensors for fundamental physics.