Progress Towards a Microwave Frequency Standard Based on Sympathetically-cooled 113Cd+ Ions

A microwave frequency standard based on
¹¹³
Cd
⁺
ions at Tsinghua University has been carried out for twelve years. To overcome the limitations of the Dick effect and the second-order Doppler frequency shift (SODFS), we propose to use heavy
¹⁷⁴
Yb
⁺
as the coolant ions to sympathetically cool the large
¹¹³
Cd
⁺
cloud, which is expected to further improve the performance of the cadmium-ion microwave frequency standard. This paper reports our recent experimental and simulation progress towards the cadmium-ion microwave frequency standard.