Demonstration of trapped single laser cooled indium ions

Abstract

Single Indium ions have been confined in a RF Paul-Straubel trap, positioned within an ultra high vacuum environment. Indium is a group IIIA atom and, in its singly ionized state, has a J = 0 $-$ J = 0 "clock" transition that is highly immune to shifts from ambient fields and field gradients. The immunity to field induced shifts, together with the tight confinement characteristic of trapped single ions, makes a single trapped laser cooled Indium ion an ideal candidate for high precision measurement and frequency standards. Indium is the first group IIIA ion to be trapped singly. The apparatus used, first to electrically detect large clouds of Indium ions, second to optically detect such clouds, and finally to optically detect single ions is described in detail. Since the "cooling" transition in $In\sp+$ is an intercombination line, laser cooling is not as strong as in other ion species that have been trapped. Therefore, successful trapping and cooling of $In\sp+$ required the use of a precooling technique for loading which is described. In addition, due to the weak cooling transition, it was essential to drastically reduce instrumental scattering background. A technique for suppressing the background and substantially increasing the signal to noise ratio, developed for this experiment, is also described. Finally, spectroscopy on the cooling transition of a single laser cooled Indium ion is given.