Fig. 3: Coherent spin control of the molecular electronic state.

a–d Spin-up difference signals Δp_↑ for four different mircowave power values as a function of pulse duration, showing clear Rabi oscillations. We note that Δp_↑ does not reach 1 since the echo sequences are performed by driving a single frequency tone while the fluctuating Overhauser field in natural silicon detunes the instantaneous resonace from the driven frequency as has been observed previously²⁰. Error bars indicate ±1σ, and black dashed lines indicate fits to a power-law decay. For the highest driving strength in d we obtain a Rabi frequency of f_R = 1.18 MHz. e The extracted Rabi frequencies as a function of microwave amplitude \({B}_{1} \sim \sqrt{{P}_{{\mathrm{MW}}}}\) show a linear dependence. f Phase control, demonstrated by a spin echo sequence in which the initial and final \(\frac{\pi }{2}\) rotations differ in phase by ϕ, producing a sinusoidal variation on the recovered spin state. Experimental parameters are P_MW = 14 dBm, t_π = 840 ns and τ = 50 ns, and the pulse sequence is indicated in the inset.