Raman sideband cooling of a Ba + 138 ion using a Zeeman interval

Motional ground state cooling and internal state preparation are important elements for quantum logic spectroscopy (QLS), a class of quantum information processing. Since QLS does not require the high gate fidelities usually associated with quantum computation and quantum simulation, it is possible to make simplifying choices in ion species and quantum protocols at the expense of some fidelity. Here, we report sideband cooling and motional state detection protocols for Ba+138 of sufficient fidelity for QLS without an extremely narrow-band laser or the use of a species with hyperfine structure. We use the two S1/2 Zeeman sublevels of Ba+138 to Raman sideband cool a single ion to the motional ground state. Because of the small Zeeman splitting, continuous near-resonant Raman sideband cooling of Ba+138 requires only the Doppler cooling lasers and two additional acousto-optic modulators. Observing the near-resonant Raman optical pumping fluorescence, we extract relevant experimental parameters and demonstrate a final average motional quantum number n≈1. We additionally employ a second, far-off-resonant laser driving Raman π pulses between the two Zeeman sublevels to provide motional state detection for QLS and to confirm the sideband cooling efficiency, measuring a final n^-=0.15(6).