State detection using coherent Raman repumping and two-color Raman transfers

We demonstrate state detection based on coherent Raman repumping and a two-color Raman state transfer. The Raman coupling during detection selectively eliminates unwanted dark states in the fluorescence cycle without compromising the immunity of the desired dark state to off-resonant scattering. We demonstrate this technique using ¹³⁷Ba⁺ where a combination of Raman coupling and optical pumping leaves the metastable state, D_3/2 |F^′′=3,m_F^′′=3〉, optically dark and immune to off-resonant scattering. All other states are strongly coupled to the upper P_1/2 levels. We achieve a single-shot state-detection efficiency of 89.6(3)% in a 1-ms integration time, limited almost entirely by technical imperfections. Shelving to |F^′′=3,m_F^′′=3〉 before detection is performed via a two-color Raman transfer with a fidelity of 1.00(3).