Portable laser-cooled ytterbium beam clock based on an ultra-narrow optical transition

TL;DR

This paper presents a portable ytterbium-based optical atomic clock utilizing an ultra-narrow transition, demonstrating high stability and robustness in field conditions, paving the way for GNSS-independent timekeeping in deployed environments.

Contribution

The development of a portable, field-operable optical atomic clock using an atom-vapor pre-stabilization and digital control for ultra-narrow transition interrogation is novel.

Findings

Achieved a frequency stability of 2×10⁻¹⁴/√τ in lab conditions.

Maintained performance after transport and at sea during field trials.

Operated continuously for multiple days without interruption.

Abstract

The highest performance atomic clocks are based on interrogation of ultra-narrow optical transitions. There is now significant interest in developing these systems as a source of GNSS-independent time in deployed, dynamic environments. We report on the development and field trial of a portable optical atomic clock interrogating the 10mHz wide $^1$S$_0\rightarrow ^3$P$_0$ transition in ytterbium-171. To enable measurement of this ultra-narrow transition in a deployed setting we combine an atom-vapor based pre-stabilization reference with all-digital control and continuous clock spectroscopy of a transversely-cooled thermal atomic beam. Characterization of the short-term frequency stability within the lab demonstrates a modified Allan deviation of $2\times 10^{-14}/\sqrt{\tau}$ for integration times up to 100s, reaching a best performance of $1.9\times 10^{-15}$ at 200s. The clock demonstrated the same performance after transport and install aboard a ship for field trial, and operated uninterrupted for multiple days whilst at sea. These results show a pathway towards truly portable optical frequency references based on the interrogation of ultra-narrow transitions.