Reconciliation of QED theory with the experimental measurements of the transition energies in the helium atom.

In the present paper, we study nonresonant corrections for experimental measurements of the transition frequencies in the helium atom. Having attracted more attention recently, such effects can make a significant contribution to experiments based on one- and two-photon atomic spectroscopy. Performing a theoretical analysis of the measurements of the $2^3S_1-3^3D_1$ transition frequency based on Doppler-free two-photon spectroscopy and the $2^3P_{0}-3^3D_{1}$ transition energy based on one-photon spectroscopy, we have found excellent agreement between the experimental and theoretical data taking into account the dominant contribution of the nonresonant correction. It is substantiated that the line profile asymmetry caused by the quantum interference of fine sub-levels of the $ 3^3D_{J} $ $ (J=1,2,3) $ state can reach tenths of a megahertz. Thus, previously unaccounted nonresonant corrections can be a potential source eliminating the imbalance in the study of helium spectra.