Vibrational spectroscopy of sympathetically laser-cooled CaH+

Abstract

Cold molecules and molecular ions are leading to a renaissance in the field of molecular spectroscopy just as laser-cooled atoms resulted in a renaissance of atomic physics. Cold molecules enable the performance of spectroscopy with unprecedented precision. Spectroscopy with cold molecules is driven by many of its modern applications such as precision measurements, cold chemistry and quantum information. Molecular ions trapped in RF Paul traps and sympathetically-cooled with laser-cooled atomic ions have been shown to be a great platform to measure spectroscopic transitions lines at a precision beyond traditional methods, where high ion density is necessary but difficult to achieve with the classical preparations. In this thesis, we perform vibrational spectroscopy on the v=10 <-v=0 and v= 9<-v = 0 overtone of a trapped and sympathetically-cooled CaH+ molecular ion using a resonance enhanced two-photon dissociation scheme. Our experiments are motivated by theoretical work that proposes comparing the vibrational overtones of CaH+ with electronic transitions in atoms to detect possible time variation of in the mass ratio of the proton-to-electron. Due to a lack of experimental data, we start the search using a broadband femtosecond Ti:Sapph laser and the guidance of theoretical calculations. Our initial spectroscopy opens the path for more precise measurements to detect the variation of proton-to-electron mass ratio and to search for astrophysical presence of CaH+. Our method ts a wide range of molecular ions that can be co-trapped and e efficiently cooled by atomic ions and is the first step to higher precision measurements. This enabled us to measure high-order vibrational overtones of a molecule using only less than 300 molecules for the entire spectrum. High precision measurements on CaH+ are enhanced by cooling down the motional temperature ion down to the motional ground state. Future high precision measurements will be conducted on narrow transitions using techniques that transforms the internal state changes into changes in temperature of the ions of CaH+.