High-Performance Microwave Frequency Standard Systems Based on the Ground-State Hyperfine Splitting of 171Yb+ and 113Cd+ Ions

Microwave frequency standards based on laser-cooled 171Yb+ and 113Cd+ ions have achieved excellent results. The fractional frequency uncertainties of ground-state hyperfine splitting frequency of 171Yb+ and 113Cd+ were \(1.8\times {10}^{-14}\) and \(6.33\times {10}^{-14}\) , respectively. The short-term stabilities of 171Yb+ microwave frequency standard and 113Cd+ microwave frequency standard are promoted to a new record level. Based on these experiment results, some defects of the system are discussed and corresponding schemes are proposed to improve the frequency accuracy. Sympathetic cooling is introduced to improve the performance of microwave frequency standard.