August 5, 2019
Cold molecular ions are good candidates for precision measurements such as the time variation of proton to electron mass ratio. However, cooling the molecular ions is challenging because of their rich internal structure. One approach is to sympathetically cool the molecular ions using laser cooled atoms and ions. To facilitate this experiment, we have developed an ion-atom hybrid trap with integrated high resolution mass spectrometer. The apparatus comprises a magneto optical trap (MOT) for potassium atoms (39K) and a linear quadrupole trap for ions. The idea is to co-trap the molecular ions with laser cooled 39K atoms and 40Ca+ ions and to sympathetically cool the molecular ion’s translational motion by cold 40Ca+ ions and rotational motion by cold 39K atoms.
We trapped laser-cooled 39K atoms and 40Ca+ ions with a good spatial overlap in our hybrid trap. We also achieved a good mass resolution, m/∆m of 208 which is sufficient to resolve the 39K+ and 40Ca+ peaks whose masses differ by only one atomic unit. Our hybrid trap is also a good platform to study ion-atom interactions governed by 1/r4 potential. In our initial experiments with the hybrid trap setup, we studied sympathetic cooling of 39K+ ions by cold 39K atoms and charge exchange collisions between 39K atoms and 40Ca+ ions. For more details see our article published in Review of Scientific Instruments (https://aip.scitation.org/doi/10.1063/1.5121431).