Figure 1

(a) Level scheme of three-level atoms. With all the atoms initially in the ground state \(| g \rangle \), a weak microwave or Raman transition (blue arrow) creates a single collective spin excitation in the storage state \(| s \rangle \). A laser pulse acting on the \(| s \rangle \to | e \rangle \) transition with Rabi frequency Ω then converts the collective spin excitation to a single-photon field E emitted on the \(| e \rangle \to | g \rangle \) transition. (b) The photon is emitted predominantly in the phase matched direction into a Gaussian mode with waist \(w_{0}\) and is collected into a fiber waveguide by paraxial optical elements