An Optical Clock Based on Coherent Population Trapping of Alkaline-earth Ions

TL;DR

This paper proposes an ultra-stable optical clock using coherent population trapping in alkaline-earth ions, employing techniques like large ion trapping and laser cooling to minimize frequency shifts and enhance stability.

Contribution

It introduces a novel optical clock design based on CPT of alkaline-earth ions with magnetic field insensitive transitions and discusses methods to improve its stability.

Findings

Insensitivity to magnetic field shifts using odd isotopes.

Use of large ion ensembles in a Paul trap for signal enhancement.

Analysis of frequency shifts and stability improvement techniques.

Abstract

An ultra-stable optical clock based on coherent population trapping effect of alkaline-earth ions, such as Ca$^+$, Sr$^+$, Ba$^+$, is analyzed here. The proposed transitions use the odd isotopes, so that the frequency shift is insensitive to the applied magnetic field. To enhance the signal, a large number of ions are trapped in a linear Paul trap, and laser cooled to crystallize such that the ions are in the Lamb-Dicke regime to avoid first order Doppler shift. Other relevant frequency shifts are also analyzed. Further techniques to improve the stability of the clock signal are discussed.