Identification of Dark Ions in Mixed Species Coulomb Crystals

The parameters of radiofrequency (Paul) traps can be configured such that particles with different charge to mass ratios can be co-trapped. Often, one of the species of trapped ions is used for all dissipative tasks, such as cooling and detection. Since the secular frequencies for each species are unique, the ions’ resonant response to an additional oscillating electric field can be used for the identification of the other, non-fluorescent ions. Using the SIMION, LAMMPS, and (py)LIon simulation software, we investigate the number of counted photons versus frequency over a range of crystal compositions. We have simulated the motion of co-trapped Be⁺, O⁺, and O₂⁺ ions in an rf trap. The Be⁺ ions’ cycling transition allows for laser cooling and fluorescence detection, both of which are included in our simulations. This will be of use in experiments whose results involve molecular dissociation or chemical reactions that form new compounds.