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Evaluation of the performance of a ${}^{40}\textrm{Ca}^+ - {}^{27}\textrm{Al}^+$ optical clock

Kaifeng Cui, Sijia Chao, Chenglong Sun, Shaomao Wang, Ping Zhang, Yuan-Fei Wei, JIAN JIAN CAO, Hualin Shu, Xue-Ren Huang

Published Dec 10, 2020• 0 citations
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Abstract

We report the evaluation of the systematic shifts and the total uncertainty of an ${}^{27}\textrm{Al}^+$ optical clock sympathetically cooled by a ${}^{40}\textrm{Ca}^+$ ion. Due to its relatively low Doppler cooling limit and the suitability of its mass ratio to the ${}^{27}\textrm{Al}^+$ ion, the time dilation shift of the secular motion of our ${}^{40}\textrm{Ca}^+ - {}^{27}\textrm{Al}^+$ clock is smaller than the shift of a ${}^{25}\textrm{Mg}^+ - {}^{27}\textrm{Al}^+$ clock. The total systematic uncertainty of our ${}^{40}\textrm{Ca}^+ - {}^{27}\textrm{Al}^+$ quantum logic clock has been estimated to be $7.6 \times 10^{-18}$, which was mainly limited by the uncertainty of the quadratic Zeeman shift.

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Optical clocks have been demonstrated to be good choices to redefine the SI ``second.'' With this goal, we have constructed a quantum-logic-based 27{}^{27}27Al\mathrm{Al}Al+{}^{+}+ ion optical clock with a fractional frequency uncertainty of $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}$. A 25{}^{25}25Mg\mathrm{Mg}Mg+{}^{+}+ ion is used as the logic ion for sympathetic cooling, state readout, and frequency-shift measurement of the 27{}^{27}27Al\mathrm{Al}Al+{}^{+}+ ion. The stability of the optical clock is $2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}/\sqrt{\ensuremath{\tau}}$, measured with a self-comparison method.
Towards a transportable Ca+^++ optical clock with a systematic uncertainty of 4.8×10−184.8\times 10^{-18}4.8×10−18
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An Al+^++ clock with 1.6×10−181.6\times10^{-18}1.6×10−18 systematic uncertainty and its frequency ratios
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