Excluding Hypothetical Light Boson Interpretation of Yb King Plot Nonlinearity with the ${}^1S_0 \leftrightarrow {}^3P_2$ Isotope Shift Measurement

TL;DR

This study performs high-precision isotope shift measurements in ytterbium to analyze King plot nonlinearity, effectively excluding hypothetical light boson explanations and enhancing the use of isotope shifts in new physics searches.

Contribution

It provides the first high-precision isotope shift data for ${}^1S_0 ightarrow {}^3P_2$ transition in Yb, enabling the exclusion of light boson interpretations of King plot nonlinearity.

Findings

Achieved sub-100 Hz linewidth in Yb spectroscopy.

Determined isotope shifts of four bosonic isotope pairs at Hz-level precision.

Excluded the light boson hypothesis as the sole cause of King plot nonlinearity.

Abstract

We present precision spectroscopy and isotope shift measurement of the ${}^1S_0 \leftrightarrow {}^3P_2$ clock transition in neutral ytterbium ($\mathrm{Yb}$) atoms. By revealing a magic wavelength at $905.4(2)$ nm, we successfully achieve the atomic spectrum narrower than $100$ Hz. The interleaved clock operation between isotopes allows us to determine isotope shifts of four bosonic isotope pairs at Hz-level uncertainties, which is combined with those of other four ultra-narrow transitions in $\mathrm{Yb}$ and $\mathrm{Yb}^+$ to construct the King plot. Importantly, the new isotope shift data reported in this work is a key to exclude the possibility of attributing the observed nonlinearity of the three-dimensional King plot solely to the new physics, while the previous works rely on the other terrestrial bound set by the neutron scattering and $(g-2)_e$ measurements. This work paves the way for the effective use of precision isotope shift data in the King plot analysis and stimulates further measurements in $\mathrm{Yb}$ and other elements.