Sympathetic cooling of ${}^4$He${}^{+}$ ions in a radiofrequency trap

B. Roth, U. Fröhlich, S. Schiller

We have generated Coulomb crystals of ultracold ${}^4$He${}^{+}$ ions in a linear radiofrequency trap, by sympathetic cooling via laser--cooled ${}^9$Be${}^{+}$. Stable crystals containing up…