$^{176}$Lu$^+$ clock comparison at the $10^{-18}$ level via correlation spectroscopy

TL;DR

This paper demonstrates a highly precise comparison between two $^{176}$Lu$^+$ optical clocks using correlation spectroscopy, achieving a fractional frequency difference uncertainty at the 10^{-18} level, and accurately measuring the quadratic Zeeman coefficient.

Contribution

The work introduces a novel correlation spectroscopy method for comparing $^{176}$Lu$^+$ clocks, achieving unprecedented precision and detailed measurement of the quadratic Zeeman effect.

Findings

Fractional frequency difference of $(-2.0 ext{±}3.7_ ext{stat} ext{±}0.9_ ext{sys}) imes 10^{-18}$ between two clocks.

Quadratic Zeeman coefficient measured as $-4.89264(88) ext{Hz/mT}^2$.

Fractional frequency uncertainty contribution of $2.5 imes 10^{-20}$ at 0.1 mT magnetic field.

Abstract

We experimentally demonstrate agreement between two $^{176}$Lu$^+$ frequency references using correlation spectroscopy. From a comparison at different magnetic fields, we obtain a quadratic Zeeman coefficient of $-4.89264(88)\,\mathrm{Hz/mT^2}$, which gives a corresponding fractional frequency uncertainty contribution of just $2.5\times 10^{-20}$ for comparisons at typical operating fields of 0.1\,mT. A subsequent comparison with both systems at 0.1\,mT, demonstrates a fractional frequency difference of $(-2.0\pm(3.7)_\mathrm{stat}\pm(0.9)_\mathrm{sys})\times10^{-18}$, where `stat' and `sys' indicate statistical and systematic uncertainty, respectively.