High Resolution Spectroscopy of the Hydrogen Atom: Determination of the1SLamb Shift

Abstract

We have measured the $1S$ Lamb shift by comparing the frequencies of the ${1S}_{1/2}-{3S}_{1/2}$ and ${2S}_{1/2}-{6S}_{1/2}$ or ${2S}_{1/2}-{6D}_{5/2}$ two-photon transitions. Our result is 8172.798 (46) MHz. It is the most precise yet reported and is consistent with the larger existing proton radius measurement of $r_p=0.862\mathrm{}\left(12\right)\mathrm{fm}$.