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

TL;DR

This paper demonstrates efficient Raman sideband cooling and motional state detection of a single $^{138}$Ba$^+$ ion using Zeeman sublevels, achieving near-ground state cooling suitable for quantum logic spectroscopy without complex laser requirements.

Contribution

It introduces a simplified Raman sideband cooling protocol for $^{138}$Ba$^+$ using Zeeman sublevels, enabling high-fidelity motional ground state preparation for quantum logic spectroscopy.

Findings

Achieved motional ground state cooling with $ar{n} \\approx 0.15$

Used only Doppler cooling lasers and two AOMs for cooling

Validated cooling efficiency via motional state detection

Abstract

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 $^{138}$Ba$^+$ of sufficient fidelity for QLS without an extremely narrowband laser or the use of a species with hyperfine structure. We use the two S$_{1/2}$ Zeeman sublevels of $^{138}$Ba$^+$ to Raman sideband cool a single ion to the motional ground state. Because of the small Zeeman splitting, near-resonant Raman sideband cooling of $^{138}$Ba$^+$ requires only the Doppler cooling lasers and two additional AOMs. Observing the near-resonant Raman optical pumping fluorescence, we estimate a final average motional quantum number $\bar{n}\approx0.17$. We additionally employ a second, far-off-resonant laser driving Raman $\pi$-pulses between the two Zeeman sublevels to provide motional state detection for QLS and to confirm the sideband cooling efficiency, measuring a final $\bar{n} = 0.15(6)$.