Trapped individual ion at absolute zero temperature.

Laser cooling and ion trapping have progressed to such an extent that one can now speak of realizing a confined atom at absolute zero temperature. In this short publication, we analyze an experiment toward such realization using a single Ba(+) ion in a miniature rf trap. The Ba(+) ion is first laser-cooled to the limit where the ion spends most of its time in the zero-point energy state. Then a test sequence allows one to verify whether or not the ion is actually in its zero-point state. The test sequence may also serve as a device for state selection of an atom at absolute zero temperature.