New Measurement of the 2S Hyperfine Interval in Atomic Hydrogen

TL;DR

This paper reports a highly precise optical measurement of the 2S hyperfine interval in atomic hydrogen, significantly reducing uncertainty and confirming QED predictions with improved accuracy.

Contribution

The study presents a new optical measurement technique that achieves unprecedented precision in determining the 2S hyperfine interval in hydrogen.

Findings

Measured 2S hyperfine interval: 177,556,834.3(6.7) Hz

Uncertainty reduced by a factor of 2.4 compared to previous measurements

Experimental value of D_{21} in good agreement with QED theory

Abstract

An optical measurement of the 2S hyperfine interval in atomic hydrogen using two-photon spectroscopy of the 1S-2S transition gives a value of 177 556 834.3(6.7) Hz. The uncertainty is 2.4 times smaller than achieved by our group in 2003 and more than 4 times smaller than for any independent radio-frequency measurement. The specific combination of the 2S and 1S hyperfine intervals predicted by QED theory $D_{21}=8 f_{\rm HFS}({2S}) - f_{\rm HFS}({1S})=48 953(3)$ Hz is in good agreement with the value of 48 923(54) Hz obtained from this experiment.