Highly efficient sympathetic cooling and charge state estimation of highly charged ions in a linear Paul trap

Abstract

Dynamic coupling between laser-cooled singly charged ions (SCIs) and highly charged ions (HCIs) in mixed-ion chains in linear Paul traps was analyzed quantitatively by molecular dynamics simulations. It was found that the external state of the HCIs is more sensitive to environmental perturbations than that of the SCIs, and that the sympathetic cooling efficiency is determined mainly by axial in-phase coupling. In addition, the precise configuration of the mixed-ion radio-frequency trapping potential and the suppression of environmental coupling in the HCIs were found to be critical for efficient sympathetic cooling. On the basis of simulated data, we propose that the relative spatial distribution of two-component SCI–HCI chains is generally related to the HCI ionization charge by a logarithmic function. This relationship can be used to nondestructively estimate the ionization charge of HCIs in a linear Paul trap at the single-charge level in real time or to predict the relative positions of the HCIs (dark ions) and precisely guide spectroscopic lasers using this information. This method can be used to study and control the quantum state of HCIs to previously unobtainable levels of precision, which will be advantageous for the development of HCI-based optical clocks, the search for variations in the fine-structure constant (α), the testing of quantum electrodynamic theory, and the search for new physics.