Ultrahigh-precision measurement of the $n=2$ triplet P fine structure of atomic helium using frequency-offset separated oscillatory fields

K. Kato, T. D. G. Skinner, E. A. Hessels

For decades, improved theory and experiment of the $n=2$ ${}^3$P fine structure of helium have allowed for increasingly-precise tests of quantum electrodynamics, determinations of th…