title: Measurement of the 2S hyperfine interval in atomic hydrogen.
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 8fHFS(2S)-fHFS(1S)=48 953(3) Hz is in good agreement with the value of 48 923(54) Hz obtained from this experiment.
authors.affiliation: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Kolachevsky
authors.forename: A
authors.initials: A
authors.lastname: Matveev
authors.forename: J
authors.initials: J
authors.lastname: Alnis
authors.forename: C G
authors.initials: CG
authors.lastname: Parthey
authors.forename: S G
authors.initials: SG
authors.lastname: Karshenboim
authors.forename: T W
authors.initials: TW
authors.lastname: Hänsch