High-accuracy multi-ion spectroscopy with mixed-species Coulomb crystals

TL;DR

This paper demonstrates high-accuracy multi-ion spectroscopy using mixed-species Coulomb crystals, achieving improved stability and low systematic uncertainties in optical clocks by simultaneous operation of multiple ions.

Contribution

It introduces a method for simultaneous spectroscopy of multiple clock ions in a Coulomb crystal, reducing instability and analyzing dead time effects, advancing multi-ion optical clock technology.

Findings

Agreement below 1×10⁻¹⁷ with single-ion results

Reduced instability from 1.6×10⁻¹⁵/√s to 9.2×10⁻¹⁶/√s with four ions

Model for decay-related dead time matching observed scaling

Abstract

Multi-ion optical clocks offer the possibility of overcoming the low signal-to-noise ratio of single-ion clocks, while still providing low systematic uncertainties. We present simultaneous spectroscopy of up to four ${}^{115}$In${}^+$ clock ions in a linear Coulomb crystal, sympathetically cooled with ${}^{172}$Yb${}^+$ ions. In first clock comparisons, we see agreement below $1\times10^{-17}$ with results obtained using a single In${}^+$ ion, for which we have evaluated the systematic uncertainty to be $2.5\times10^{-18}$. Operation with four clock ions reduces the instability from $1.6\times10^{-15}/\sqrt{t/(1\;\mathrm{s})}$ to $9.2\times10^{-16}/\sqrt{t/(1\;\mathrm{s})}$. We derive a model for decay-related dead time during state preparation, which matches the observed scaling of instability with clock ion number $N$, and indicates that $1/\sqrt{N}$ scaling can be achieved with the addition of a repump laser.