Sympathetic cooling of 9 Be + and 24 Mg + for quantum logic

We demonstrate the cooling of a two species ion crystal consisting of one ${}^{9}{\mathrm{Be}}^{+}$ and one ${}^{24}{\mathrm{Mg}}^{+}$ ion. Since the respective cooling transitions of these two species are separated by more than 30 nm, laser manipulation of one ion has negligible effect on the other even when the ions are not individually addressed. As such this is a useful system for reinitializing the motional state in an ion trap quantum computer without affecting the qubit information. Additionally, we have found that the mass difference between ions enables a method for detecting and subsequently eliminating the effects of radio frequency micromotion.