CHEN Xing, XUE Xiaobo, MENG Jing, JIANG Yiqin, SHANG Haosen, HAN Lei, SUN Jingxin, JI Qianqian, ZHANG Shengkang, GE Jun
High-precision time and frequency standards are critical for time synchronization and navigation/positioning accuracy in key fields such as global navigation satellite systems (GNSS), transportation systems, power systems, and network systems. Optical atomic clocks exhibit uncertainty metrics two orders of magnitude higher than the current primary standard, the cesium fountain clock, and their adoption for redefining the SI second has been formally proposed. The ytterbium ion optical clock, possessing two clock transition spectrums both adopted as secondary representations of the second, is one of the leading candidate ion systems for the future definition of the second. The ytterbium ion system has significant advantages, including high sensitivity to fundamental physical constants, a high clock transition quality factor, and relatively simplified laser requirements. These characteristics confer substantial potential in fundamental physics research, performance metric enhancement, and engineering applications, gaining widespread attention from research institutions worldwide. This article describes the operating principle of the ytterbium ion optical clock, reviews the key physical effects that constrain the performance of the system and the corresponding suppression methods, summarizes research progresses in fundamental physical exploration, breakthroughs in core performance metrics, and engineering technologies, and discusses prospects for its future development.
