Figure 7: Schematic summary of the conversion process from incident coherent light (wavy arrow) to electron spins and further conversion to the single photon output. Polarization of photon is well preserved in the generated positive trion spins under the quasi-resonant excitation. The spin flip between the trion states with the opposite spin alignments will limit the spin preservation, but this influence is much reduced in the present trion state. The estimated fidelity, corresponding to the DCP of 0.85, is as high as 0.96.