MPI Campus Seminar: Precision spectroscopy on molecular hydrogen

Precise measurements of vibrational transition frequencies in the isotopes of molecular hydrogen can provide a sensitive probe of fundamental physics. Because these transition frequencies can be predicted with high accuracy using high-level ab-initio theory, comparisons between theory and experiment can be used to test quantum electrodynamics, search for new physics, and determine the nucleon-electron mass ratios more precisely. In this talk, I will present our recent measurements of two specific transitions: v=0, N=0 to v=1, N=1 in HD and v=0, N=0 to v=1, N=2 in D₂. Previous measurements of these transitions have determined their frequencies with an uncertainty of ~60 parts per billion (ppb), and the best ab-initio theory has predicted the transition frequencies with an uncertainty of 4-5 ppb. Our recent measurements push the experimental uncertainties down to 0.1 and 0.2 ppb, respectively, and uncertainties in the 0.01 ppb range are expected with minor improvements to the experimental setup. Such measurements, together with a corresponding improvement in the ab-initio theory, could produce the most precise estimates of the proton-electron and deuteron-electron mass ratios.