## (a) Time evolution of the population of the D_{3/2} (red dotted line), P_{1/2} (**×** 10^{4}, green solid line), S_{1/2} (**×** 10^{2}, black dashed line) and D_{5/2} (dot-dashed blue line) states during the STIRAP process driven by the Gaussian pulses Ω_{B}(*t*) and Ω_{R}(*t*) (see equation (6))

**Figure 3.** (a) Time evolution of the population of the D_{3/2} (red dotted line), P_{1/2} (**×** 10^{4}, green solid line), S_{1/2} (**×** 10^{2}, black dashed line) and D_{5/2} (dot-dashed blue line) states during the STIRAP process driven by the Gaussian pulses Ω_{B}(*t*) and Ω_{R}(*t*) (see equation (6)). Laser parameters are τ = Δ*t* = 20 μs, Ω_{C}/2π = 10 MHz, Δ_{C}/2π = 100 MHz, \Omega _B^0/2\pi =400 MHz, Δ_{B}/2π = 100 MHz, \Omega _R^0/2\pi =40 MHz, Δ_{R} = Δ_{B} − Δ_{C} − α_{C}Ω_{C}/2. (b) Time evolution of the Rabi frequency Ω_{B}(*t*) (blue dashed line) and Ω_{R}(*t*) (red solid line); Ω_{C} is constant during the STIRAP process.

**Abstract**

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.