Ba+: Coherent excitation of an E2 transition
A more “traditional” avenue towards quantum computation with trapped ions is to employ an optical transition as a qubit. Since the relaxation rates of the states acting as a qubit eventually limit the time available for coherent manipulation, the use of two states connected via an electric dipole allowed transition is not a good choice. Therefore, the electronic ground state of an ion (usually one speciﬁc Zeeman sublevel) and a metastable excited state have been chosen as qubit states in various experiments (Appasamy et al. 1998, Roos et al. 1999, Barton et al. 2000). Here, we report on experiments with Ba+ and 172Yb+ ions where the electric quadrupole (E2) resonance 2S1/2- 2D5/2 serves as the qubit.