Part of the dressed state picture relevant for the three-photon resonance condition, giving rise to the coherent dark state
Figure 2. Part of the dressed state picture relevant for the three-photon resonance condition, giving rise to the coherent dark state. The straight lines stand for laser couplings and the wavy lines for radiative decay (see the text for details).
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.