Sympathetic Crystallization of Trapped Ions

We have created multispecies Coulomb crystals in a linear Paul trap containing up to a few hundred ions of which more than $50\%$ were cooled only sympathetically through the Coulomb interaction with laser-cooled ${\mathrm{Mg}}^{+}$ ions. In an extreme case, one laser-cooled ion maintained order in a 15 ion string. Ion species segregation was obtained by radiation pressure. Previous experiments and molecular dynamics simulations suggest the temperature is 10 mK or lower. These results indicate that a wide range of atomic and molecular ions can be cooled and localized in linear Paul traps which is important for improvements in spectroscopic studies of such ions.