Sympathetic cooling of trapped ions: A laser-cooled two-species nonneutral ion plasma

Sympathetic cooling of trapped ions has been demonstrated in an experiment where ^198Hg^+ ions were confined in a Penning ion trap with laser-cooled ^9Be^+ ions. ^198Hg^+ temperatures below 1 K were achieved. Ion plasma sizes, shapes, and rotation frequencies were measured. Dramatic changes in the ^9Be^+ plasma were observed when the ^198Hg^+ ions were introduced into the trap. These observations are consistent with the prediction of centrifugal separation for ions of different charge-to-mass ratios.