Le vendredi 12 mars à 14H en visioconférence :https://zoom.us/j/99027760204?pwd=bkx1ZWlRWEx5WGp0cEtEV3RBK25Gdz09
Hyperfine structure in the hydrogen molecular ions
The hydrogen molecular ions H2+ and HD+ are promising systems for the metrology of fundamental constants. A Doppler-free two-photon vibrational transition in HD+ was recently measured at Amsterdam VU with an uncertainty of about 3 parts per trillion (ppt), whereas QED theoretical predictions have reached uncertainties of 7-8 ppt. In order to determine the transition frequencies from experimental spectra, various systematic effects have to be considered. In the first part of this thesis, I calculated one of the main systematic effects, namely the AC Stark shift induced by the different lasers used in the experiment.
A spin-averaged transition frequency was then deduced from the measured hyperfine components, and compared with theoretical predictions, which allowed an improved determination of the proton-electron ratio with an uncertainty of 21 ppt. This required an improved theoretical description of the hyperfine structure, which is the object of the second part of the thesis. The theoretical accuracy was limited by the spin-orbit and spin-spin tensor interactions. The calculation of higher-order relativistic corrections to these interaction terms, following the NRQED approach, is presented in detail. Improved theoretical values of the spin-orbit and spin-spin tensor interaction coeffcients are obtained and compared with available experimental data. Very good agreement is observed in the case of H2+, whereas some yet unexplained discrepancies are observed in HD+.