Multiple strategies for evaluating the uncertainty of blackbody radiation frequency shift in an optical clock

The Stark shift due to the blackbody radiation (BBR) is a crucial obstacle limiting the performance of optical clocks. Here five different methods are reported to evaluate an ytterbium (Yb) clock's BBR shift in the same science chamber for the first time. The intercomparison shows that incorporating in-chamber temperature information can reduce the uncertainty by one order of magnitude. Notably, a simulation model is developed and optimized through calibration with in-chamber sensors, which can suppress the BBR uncertainty close to 1 × 10⁻¹⁸ at room temperature and provide more credible results. Moreover, the 10⁻¹⁹ level uncertainty is further identified by surrounding the atoms in the cryogenic environment. It is worth noting that the above results were obtained without BBR shield and external temperature control. These comprehensive evaluation results provide a valuable reference for different uncertainty requirements or building advanced optical clocks towards total uncertainty in the 10⁻¹⁹ region.