Knowledge Bank

The search for time variation in the fundamental constants of nature such as the fine structure constant($\alpha$) and the proton/electron mass ratio($\mu$), is an area of active research.Comparing the vibrational overtones of CaH$+$ with electronic transitions in atoms has been proposed as a means to detect possible time variation of $\mu$ . Before these precision measurements can be realized, the survey spectroscopy needs to be performed. We describe our experiments using a Coulomb crystal of sympathetically cooled CaH$+$ and laser-cooled Ca$+$ ions to measure the vibrational overtones by resonance-enhanced multiphoton photo-dissociation (REMPD) in a linear Paul trap. The dissociation of CaH$+$ is detected by observing the change in the crystal composition by monitoring the Ca$+$ fluorescence. Future single ion experiments for the precision measurement are also discussed.