Abstract:

The performance of the rubidium (Rb) atomic frequency standard has achieved significant improvement in recent years. Its frequency stability has already reached the order of 10^-13τ^-1/2. To further improve Rb frequency standard's stability performance, we developed a high signal-to-noise ratio (SNR) physics package whose cavity-cell assembly consists of a slotted-tube microwave cavity, separated filter and absorption cells. The microwave cavity has a homogenous field distribution along the quantization axis, and the filter and absorption cells are temperature-controlled independently. We also used an optical and isotopic filtering scheme to suppress shot noise from the pumping light. The physics package's final background photocurrent I₀ and the frequency discrimination slope K_dwere measured to be 95 μA and 7.7 nA/Hz, respectively, and the calculated limit stability of the shot noise of the physical package was 7.5×10^-14τ^-1/2. The result shows that Rb frequency standard can reach an unprecedented stability level below 1×10^-13τ^-1/2 as long as the electronic system's noise could be well controlled.

Key words: rubidium atomic frequency standards, physics package, slotted-tube cavity, shot noise, frequency stability