Figure 1
APS/Alan Stonebraker

Figure 1: Scheme of the optical transitions in a quantum dot containing an individual magnetic atom and 0 (Mn), 1 (X-Mn), or 2 (X2-Mn) excitons. The exciton states are split by the exchange interaction with the Mn spin, whereas in the ground (Mn) and biexciton (X2-Mn) states, the energy levels result from the fine and hyperfine structure of the Mn spin. Spin-population trapping on the 5/2 level is achieved by carefully tuning a resonant CW laser (green arrow). Spin readout: A direct resonant excitation of the biexciton is performed by a pulsed two-photon absorption through an intermediate virtual state (blue arrows). The biexciton photon emission allows monitoring all six Mn spin levels simultaneously.