Key points are not available for this paper at this time.
A single trapped ^198Hg^+ ion was cooled by scattering laser radiation that was tuned to the resolved lower motional sideband of the narrow ^2S₁₂-^2D₅₂ transition. The different absorption strengths on the upper and lower sidebands after cooling indicated that the ion was in the ground state of its confining well approximately 95% of the time.
Diedrich et al. (1989) studied this question.