Absolute Test of Quantum Electrodynamics for Helium-Like Vanadium

Absolute measurements of the energies of helium-like vanadium resonances on an electron beam ion trap (EBIT) are reported. The results agree with recent theoretical calculations and the experimental precision (27–40 ppm) lies at the same level as the current uncertainty in theory (0.1 eV). The measurements represent a 5.7%–8% determination of the quantum electrodynamics (QED) contribution to the transition energies and are the most precise measurements of the helium-like resonances in the Z = 19–31 range. These are the first precision X-ray measurements on the National Institute of Standards and Technology EBIT and strongly commend the EBIT as a new spectroscopic source for QED investigations.