Two-photon spectroscopy of hydrogen molecular ions for precision measurements of fundamental constants

摘要

This contribution discusses a double resonance two-photon spectroscopy scheme on trapped HD+ that provides detection of a two-photon rotational transition and a two-photon rovibrational transition by dissociation. The two-photon lineshapes are calculated using a rate equation model for HD+ ions populations. The resolution is at better than the 10^{-12level. The total lightshift for selected hyperfine components of the two-photon rotational transition is evaluated using the two-photon operator formalism. The lightshift of the rotational transition may be cancelled by adjusting the intensity of the laser that probes the rovibrational transition in the double resonance spectroscopy scheme. The experimental accuracy with two-photon transitions of trapped HD+ ions is at the 10-12level, which corresponds also to the accuracy of theoretical calculations. The comparison of experimental data and theoretical calculations for HD+and H₂+may provide an independent and accurate determination of the Rydberg constant, the proton-to-electron mass ratio and the deuteron-to-proton mass ratio, respectively. It provides an alternative way for the measurement of the proton and deuteron radii. Depending on possible issues of the proton radius puzzle in atomic spectroscopy, two-photon spectroscopy of hydrogen molecular ions may lead to an improvement of the determination of the proton-to-electron mass ratio and deuteron-to-proton mass ratio beyond the 10-11level.}