A compact, transportable optical clock with 1×10−17 uncertainty and its absolute frequency measurement
Jian Cao, Jinbo Yuan, Shaomao Wang, Ping Zhang, Yi Yuan, Daoxin Liu, Kaifeng Cui, Sijia Chao, Hualin Shu, Yige Lin, Shiying Cao, Yuzhuo Wang, Zhanjun Fang, Fang Fang, Tianchu Li, Xue-Ren Huang
Abstract
We report a robust, compact, and transportable optical clock (TOC-729-2) based on a trapped single 40Ca+ ion with a systematic uncertainty of 1.1×10−17, which is limited by the black-body radiation shift uncertainty at room temperature. By comparing it with the previous transportable optical clock (TOC-729-1) similar but completely independent, the instability was measured to be better than 1.2×10−14/τ. Benefiting from the modular and integrated design, this TOC was constructed in a volume of ∼0.33 m3 excluding the controlling electronics in 19-in. racks. After being moved ∼1200 km away by express delivery, the single-ion signal was restored within 24 h. With the TOC uptime of 92% in 35-day period, the absolute frequency of the 729 nm transition of 40Ca+ was measured using a satellite link to International Atomic Time (TAI) to provide traceability to the SI second, and the result is 411 042 129 776 400.15(22) Hz, corresponding to a relative uncertainty of 5.3×10−16.