Liquid-Nitrogen-Cooled ${​}^{40}{\mathrm{Ca}}^{+}$ Ion Optical Clock with a Systematic Uncertainty of $4.4×{10}^{−19}$

Author(s): Bao-lin Zhang, Zi-xiao Ma, Yao Huang, Hui-li Han, Ru-ming Hu, Yu-zhuo Wang, Hua-qing Zhang, Li-yan Tang, Ting-yun Shi, Hua Guan, and Ke-lin Gao We report a single-ion optical clock based on the $4{S}_{1/2}→3{D}_{5/2}$ transition of the $^{40}{\mathrm{Ca}}^{+}$ ion, operated in a liquid nitrogen cryogenic environment, achieving a total systematic uncertainty of $4.4×{10}^{−19}$. We employ a refined temperature evaluation scheme to reduce the… [Phys. Rev. Lett. 136, 053202] Published Tue Feb 03, 2026