High-Performance Microwave Frequency Standard Based on Sympathetically Cooled Ions

TL;DR

This paper presents the first sympathetically-cooled ion microwave frequency standard using laser-cooled calcium ions to cool cadmium ions, significantly improving stability and accuracy over previous direct cooling methods.

Contribution

It introduces a novel sympathetically-cooled ion frequency standard with enhanced stability and lower uncertainty, demonstrating its potential for advanced microwave standards.

Findings

Achieved coherence lifetime over 40 seconds

Short-term frequency stability of 3.48×10⁻¹³/√τ

Uncertainty of 1.5×10⁻¹⁴, surpassing direct cooling standards

Abstract

The ion microwave frequency standard is a candidate for the next generation of microwave frequency standard with the potential for very wide applications. The Dick effect and second-order Doppler frequency shift (SODFS) limit the performance of ion microwave frequency standards. The introduction of sympathetic cooling technology can suppress the Dick effect and SODFS and improve the stability and accuracy of the frequency standard. However, the sympathetically-cooled ion microwave frequency standard has seldom been studied before. This paper reports the first sympathetically-cooled ion microwave frequency standard in a Paul trap. Using laser-cooled ${}^{40}\mathrm{{Ca}}^{+}$ as coolant ions, ${}^{113}\mathrm{{Cd}}^{+}$ ion crystal is cooled to below 100 mK and has a coherence lifetime of over 40 s. The short-term frequency stability reached $3.48 \times 10^{-13}/\tau^{1/2}$, which is comparable to that of the mercury ion frequency standard. Its uncertainty is $1.5\times 10^{-14}$, which is better than that of directly laser-cooled cadmium ion frequency standard.