Ramsey Spectroscopy of the 2S1/2 Hyperfine Interval in Atomic Hydrogen

The 2S1/2 hyperfine interval in atomic hydrogen was measured using Ramsey spectroscopy with a thermal beam cooled to cryogenic temperatures. The measured value is 177 556 838.87(85) Hz, which represents the most precise determination of this interval to date. The 1S1/2 hyperfine interval f(1S1/2) and the 2S1/2 hyperfine interval f(2S1/2) can be combined to give the quantity D21=8f(2S1/2)−f(1S1/2), which mostly eliminates uncertainty due to nuclear structure effects and is well described by bound-state quantum electrodynamics. Using the value of f(2S1/2) from this work gives a value of D21expt=48 959.2(6.8) Hz, which is in agreement with the theoretical value of D21Theory=48 954.1(2.3) Hz.Received 9 February 2023Accepted 4 April 2023DOI:https://doi.org/10.1103/PhysRevLett.130.203001© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtomic spectraBound statesFine & hyperfine structureHypothetical particle physics modelsParticle dark matterAtomic, Molecular & OpticalParticles & FieldsGravitation, Cosmology & Astrophysics