Anne Curtis (NPL)
Optical atomic clocks: progress towards a new SI second and tests of fundamental physics
The accuracy and stability of atom-based optical frequency standards make them an ideal metrological tool, with numerous applications in areas requiring precise position, navigation and timing. Measurements involving more than one optical clock - whether locally or utilising clocks in different laboratories or countries via interconnected fibre networks - can enable a direct exploration of clock performance at the part-in-1017 level and below. Repeatability of the results year on year gives added confidence in how well a clock system and its long-term behaviour are understood - an essential step for redefining the SI second in terms of an optical frequency. The culture of sharing increasingly long-term measurement data has also enabled analysis of clock frequency data on a variety of different timescales, which has great potential for testing fundamental physics theories.
In this seminar I will introduce you to the basics of frequency metrology and the inner workings of optical atomic clocks. I will work to motivate my current experimental research at NPL, which utilises the long-lived electric octupole (E3) transition the 171Yb+ ion, with which we have produced a frequency standard with a reported uncertainty of 2.2 x 10-18 [1]. This work at NPL supports the international efforts to redefine the SI second [2], and I will share results of recent absolute frequency measurements, optical frequency ratio measurements with other optical clocks, performed locally and at great distance, and improvements in automation and robust operation of our 171Yb+ clock system. Finally, I will also show how such frequency measurements have been used to constrain temporal variation of the fine structure constant and exclude regions of parameter space in theories beyond the Standard Model, such as those which include ultralight scalar dark matter [3,4].
References
[1] A Tofful et al., “171Yb+ optical clock with 2.2 x 10-18 systematic uncertainty and absolute frequency measurements,” Metrologia 61, 045001 (2024).
[2] N Dimarcq et al., “Roadmap towards the redefinition of the second,” Metrologia 61 012001 (2024).
[3] BM Roberts, et al., “Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks,” New J. Phys. 22, 093010 (2020).
[4] N Sherrill, AO Parsons, et al., “Analysis of atomic-clock data to constrain variations of fundamental constants,” New J. Phys. 25 093012 (2023).