N-level scheme in the dressed state picture: the states |D〉, |P〉, |S〉 coupled by laser couplings ΩR and ΩB form a Λ-configuration; state |S〉 couples weakly to the metastable state |Q〉 by ΩC
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Figure 1. N-level scheme in the dressed state picture: the states |D〉, |P〉, |S〉 coupled by laser couplings ΩR and ΩB form a Λ-configuration; state |S〉 couples weakly to the metastable state |Q〉 by ΩC. The wavy lines indicate the radiative decay. Parameters and possible atomic species are discussed in the text.
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 × 10−5) with realistic parameters. The scheme is also extended to the synthesis of a linear combination of three stable or metastable states.