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

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.

Figures (3)

• Figure 1: Temperature measurements of the LNCIOC $\mathrm{Ca}^{+}\!\text{-}2$ ion optical clock 2. The abrupt temperature increases are due to the periodic refilling of liquid nitrogen.
• Figure 2: Red- and blue-sideband Rabi oscillations for the three motional modes after SBC. The orange dots represent the experimentally measured transition probabilities, and the blue solid lines are thermal-distribution fits to these data.
• Figure 3: Measurement of the heating rates.Panels (a), (c), and (e) present red-sideband Rabi oscillations of the $X$-, $Y$-, and $Z$-motional modes, respectively, measured at different dark times following SBC. By fitting these curves with thermal-distribution models, the mean occupation numbers at different delays are extracted. (b), (d), and (f) show linear fits to the data in (a), (c), and (e), respectively. The slope of each fit corresponds to the heating rate, and the intercept gives the mean occupation number after SBC. All fit results include 95% confidence intervals as uncertainty estimates.