Single-ion, transportable optical atomic clocks

TL;DR

This paper reviews recent advances in transportable single-ion optical atomic clocks, highlighting their components, potential for compactness, and future applications in field measurements and clock networks.

Contribution

It provides a comprehensive overview of recent developments in key components and projects related to transportable single-ion optical clocks, emphasizing their potential for practical deployment.

Findings

Advances in ion trap and ultra-stable cavity technology

Development of transportable single-ion optical clock prototypes

Potential applications in field measurements and clock networks

Abstract

For the past 15 years, tremendous progress within the fields of laser stabilization, optical frequency combs and atom cooling and trapping have allowed the realization of optical atomic clocks with unrivaled performances. These instruments can perform frequency comparisons with fractional uncertainties well below $10^{-17}$, finding applications in fundamental physics tests, relativistic geodesy, and time and frequency metrology. Even though most optical clocks are currently laboratory setups, several proposals for using these clocks for field measurements or within an optical clock network have been published, and most of time and frequency metrology institutes have started to develop transportable optical clocks. For the purpose of this special issue, we chose to focus on trapped-ion optical clocks. Even though their short-term fractional frequency stability is impaired by a lower signal-to-noise ratio, they offer a high potential for compactness: trapped ions demand low optical powers and simple loading schemes, and can be trapped in small vacuum chambers. We review recent advances on the clock key components, including ion trap and ultra-stable optical cavity, as well as existing projects and experiments which draw the picture of what future transportable, single-ion optical clocks may resemble.