Improved Measurement of the Hydrogen 1S - 2S Transition Frequency

TL;DR

This paper reports a highly precise measurement of the hydrogen 1S - 2S transition frequency using two-photon spectroscopy, significantly improving the accuracy over previous measurements by linking the laser to a cesium clock.

Contribution

The study presents a new measurement of the hydrogen 1S - 2S transition frequency with over threefold increased precision compared to prior work.

Findings

Fractional frequency uncertainty of 4.2×10⁻¹⁵

Transition frequency measured as 2,466,061,413,187,035 Hz

Laser frequency linked to cesium fountain clock via frequency comb

Abstract

We have measured the 1S - 2S transition frequency in atomic hydrogen via two photon spectroscopy on a 5.8 K atomic beam. We obtain $f_{1S-2S} = 2 466 061 413 187 035 (10)$ Hz for the hyperfine centroid. This is a fractional frequency uncertainty of $4.2\times 10^{-15}$ improving the previous measure- ment by our own group [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)] by a factor of 3.3. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb.