<em>N</em>-level scheme in the dressed state picture: the states |D〉, |P〉, |S〉 coupled by laser couplings Ω<sub><em>R</em></sub> and Ω<sub><em>B</em></sub> form a Λ-configuration; state |S〉 couples weakly to the metastable state |Q〉 by Ω<sub><em>C</em></sub>

<p><strong>Figure 1.</strong> <em>N</em>-level scheme in the dressed state picture: the states |D〉, |P〉, |S〉 coupled by laser couplings Ω<sub><em>R</em></sub> and Ω<sub><em>B</em></sub> form a Λ-configuration; state |S〉 couples weakly to the metastable state |Q〉 by Ω<sub><em>C</em></sub>. The wavy lines indicate the radiative decay. Parameters and possible atomic species are discussed in the text.</p> <p><strong>Abstract</strong></p> <p>A stimulated Raman adiabatic passage (STIRAP)-like scheme is proposed to exploit a three-photon resonance taking place in alkaline-earth-metal ions. This scheme is designed for state transfer between the two fine structure components of the metastable D-state which are two excited states that can serve as optical or THz qubit. The advantage of a coherent three-photon process compared to a two-photon STIRAP lies in the possibility of exact cancellation of the first-order Doppler shift which opens the way for an application to a sample composed of many ions. The transfer efficiency and its dependence with experimental parameters are analysed by numerical simulations. This efficiency is shown to reach a fidelity as high as (1–8 <b>×</b> 10<sup>−5</sup>) with realistic parameters. The scheme is also extended to the synthesis of a linear combination of three stable or metastable states.</p>