Metrology in a two-electron atom: The ionization energy of metastable triplet helium (${2{}^3\mathbf{S}}_1$)

Gloria Clausen, Kai Gamlin, Josef A. Agner +2

Helium (He) is the ideal atom to perform tests of ab-initio calculations in two-electron systems that consider all known effects, including quantum-electrodynamics and nuclear-size…