Multiply charged thorium crystals for nuclear laser spectroscopy

We have produced laser-cooled crystals of {sup 232}Th{sup 3+} in a linear rf Paul trap. This is the first time that a multiply charged ion has been laser cooled. Our work opens an avenue for excitation of the nuclear transition in a trapped, cold {sup 229}Th{sup 3+} ion. Laser excitation of nuclear states would establish a new bridge between atomic and nuclear physics, with the promise of new levels of metrological precision.