A Liquid-Nitrogen-Cooled Ca+ Ion Optical Clock with a Systematic Uncertainty of 4.4E-19

TL;DR

This paper presents a highly precise 40Ca+ ion optical clock operated in a liquid nitrogen cryogenic environment, achieving a systematic uncertainty of 4.4E-19 through advanced temperature control and cooling techniques.

Contribution

It introduces a cryogenic ion clock with reduced systematic uncertainties and improved stability, utilizing refined BBR evaluation and sideband cooling methods.

Findings

Achieved a systematic uncertainty of 4.4E-19.

Reduced blackbody radiation uncertainty through refined temperature evaluation.

Reported the lowest ambient electric field noise heating rate in trapped-ion clocks.

Abstract

We report a single-ion optical clock based on the 4S_1/2-3D_5/2 transition of the 40Ca+ ion, operated in a liquid nitrogen cryogenic environment,achieving a total systematic uncertainty of 4.4E-19. We employ a refined temperature evaluation scheme to reduce the frequency uncertainty due to blackbody radiation (BBR), and the 3D sideband cooling has been implemented to minimize the second-order Doppler shift. We have precisely determined the average Zeeman coefficient of the 40Ca+ clock transition to be 14.345(40) Hz/mT^2, thereby significantly reducing the quadratic Zeeman shift uncertainty. Moreover, the cryogenic environment enables the lowest reported heating rate due to ambient electric field noise in trapped-ion optical clocks.