Beads on a string: experiments with a linear rf ion trap

Abstract

Trapping and cooling large numbers of ions, each confined to much less than an optical wavelength, is of great interest for high accuracy spectroscopy, improved frequency standards and atom-radiation field experiments. This can be achieved in a linear rf ion trap where the rf electric fields go to zero along a line rather than at only a point. As a step toward this goal we have constructed a linear trap and have observed simple crystallized linear structures of up to tens of 199Hg+ ions. By varying the axial well depth (determined by a static potential) we have also observed more complex crystallized structures. The ion positions in these structures are in close agreement with a calculation that used as input the measured secular frequencies of the trap. We have also observed the 40.5-GHz ground-state hyperfine transition of trapped 199Hg+ ions by microwave/optical double resonance.