Direct laser cooling Al+ ions optical clocks

TL;DR

This paper proposes a direct laser cooling scheme for Al$^+$ ions optical clocks, enhancing both their stability and accuracy by using two traps and advanced cooling techniques, potentially leading to the most precise optical clock.

Contribution

It introduces a novel direct laser cooling method for Al$^+$ ions optical clocks utilizing two traps and dual-stage cooling, improving stability and accuracy over existing indirect methods.

Findings

Clock laser stability can reach 9.0×10^{-17}/√τ.

Systematic uncertainty can be reduced to 1×10^{-18}.

Potential to become the most accurate and stable optical clock.

Abstract

Al$^+$ ions optical clock is a very promising optical frequency standard candidate due to its extremely small blackbody radiation shift. It has been successfully demonstrated with indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of Al$^+$ ions optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al$^+$ ions traps are utilized. The first trap is used to trap a large number of Al$^+$ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al$^+$ ions to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167 nm laser. The expected clock laser stability can reach $9.0\times10^{-17}/\sqrt{\tau}$. For the second trap, in addition to 167 nm laser Doppler cooling, a second stage pulsed 234 nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about $1\times10^{-18}$. The proposed Al$^+$ ions optical clock has the potential to become the most accurate and stable optical clock.