Science ( IF 41.845 ) Pub Date : 2020-07-30 , DOI: 10.1126/science.aba0453 Sayan Patra, M. Germann, J.-Ph. Karr, M. Haidar, L. Hilico, V. I. Korobov, F. M. J. Cozijn, K. S. E. Eikema, W. Ubachs, J. C. J. Koelemeij
Recent mass measurements of light atomic nuclei in Penning traps have indicated possible inconsistencies in closely related physical constants like the proton-electron and deuteron-proton mass ratios. These quantities also influence the predicted vibrational spectrum of the deuterated molecular hydrogen ion in its electronic ground state. We measure the frequency of the v = 0→9 overtone transition of this spectrum with an uncertainty of 2.9 parts-per-trillion through Doppler-free two-photon laser spectroscopy. Leveraging high-precision ab initio calculations we convert our measurement to tight constraints on the proton-electron and deuteron-proton mass ratios, consistent with the most recent Penning-trap determinations of these quantities. This results in an unprecedented precision of 21 parts-per-trillion for the value of the proton-electron mass ratio.