Fig. 4.

Electron spin initialisation fidelity. a Experimental sequence. Before each round, the ground state spin is depolarised using off-resonant excitation for 40 µs. Then, the system is initialised into ${∣-\frac{1}{2}⟩}_{\mathrm{gs}}$. Ground state populations are inferred from Rabi oscillations and resonant optical readout. b Left side: Spin population in ${∣-\frac{1}{2}⟩}_{\mathrm{gs}}$ as a function of the duration of the initialisation procedure. Up to 97.5% are achieved. The blue line is a fit using an exponential function. The error bars are estimated from the uncertainties in determining populations of the ground spin states, assuming that the main source of error is shot noise. Right side: Inferred spin populations in the four ground state sublevels without initialisation (top) and after 80 µs initialisation time