Optical lattice clocks for fundamental physics and redefinition of the second

Atomic clocks are the most precise timekeeping devices. They work by stabilizing the frequency of some electromagnetic radiation so that it matches the frequency of an atomic energy level transition. Clocks based on Caesium 133 atoms provide the definition of the second in the international system of units and are used to realise Universal Coordinated Time and in technologies that require accurate timekeeping such as satellite navigation.

Optical clocks work on the same principle as atomic clocks with the difference that they use radiation in the optical domain which has a higher frequency. The increased sensitivity that comes with this means that atoms need to be very carefully cooled down to uK temperatures, and optical lattice clocks also use optical light to trap atoms in a low kinetic energy state. These clocks are currently under development to become more reliable and robust but have already demonstrated higher precision than normal atomic clocks. This suggests that a new definition of the second will be needed so that the realisation of the second can be done using the more precise optical clocks. Another aspect of this increased precision that generates interest is the possibility of performing very accurate geodesy and investigating elusive phenomena such as variations in fundamental constants and dark matter.

The objectives of this project are to contribute to the effort to redefine the second and to the fundamental Physics research by demonstrating clock operation with improved stability and by performing measurements of frequency ratios of clocks with different species (namely Strontium and Ytterbium ion) with enhanced precision.

The novelty of the research stems from the new techniques employed to reduce the noise in the laser stabilization process. The limits of clock performance will be characterised by a mixture of theoretical considerations, newly developed computer simulations and experiments to investigate optimal operating parameters for an individual clock as well as composite architectures which combine two clocks to produce a more stable result than what is possible with a single clock. The solutions will propose changes in how the clock(s) is operated rather than changes to the experimental hardware.

This work will be conducted at the National Physical Laboratory which is the metrology institute for the UK focusing on producing standards for measurement and calibration, and will also involve other metrology institutes in Europe, America and Asia through international measurement campaigns.