Liquid-Nitrogen-Cooled 40Ca+ Ion Optical Clock with a Systematic Uncertainty of 4.4×10−19RemoveBao-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 GaoPhys. Rev. Lett. 136, 053202 (2026)
