Phys.Rev.Lett. 136, 243001 (2026)

K.Steinebach, J.C.J.Koelemeij, H.L.Bethlem, K.S.E.Eikema

Spectroscopy of ⁴He at 0.25 ppt Uncertainty and Improved Alpha-Helion Charge-Radius Difference Determination

ATOMIC PHYSICS ⁴He; measured transition frequency using a Bose-Einstein condensed sample confined in a magic-wavelength optical dipole trap. ^3,4He; deduced the most precise determination to date of the charge-radius difference between the helion and alpha particle, the current discrepancy between QED theory and experimentally observed ionization energies of excited states in helium is not apparent in the isotope shift. Comparison with available data.

doi: 10.1103/rwg9-my6x