Nonresonant corrections for the hydrogen atom

Abstract
The nonresonant (NR) corrections are estimated for the 1s–2p one-photon and for the 1s–2s two-photon resonances in the hydrogen atom. These corrections depend on the measurement process and set the limit for the accuracy of atomic frequency measurements. With the measurement process accepted in recent experiments the NR contribution for the 1s–2s transition energy can reach 10–3 Hz while the experimental inaccuracy is quoted to be ±46 Hz. PACS Nos.: 31.30Jv, 12.20Ds, 06.20Jr, 31.15-p