The main limitation to the high-fidelity quantum control of spins in semiconductors is the presence of strongly fluctuating fields arising from the nuclear spin bath of the host material. We demonstrate here a substantial improvement in single-qubit inversion fidelities for an electron spin qubit bound to a 31P atom in natural silicon, by applying adiabatic sweeps instead of narrow-band pulses. We achieve an inversion fidelity of 97%, and we observe signatures in the spin resonance spectra and the spin coherence time that are consistent with the presence of an additional exchange-coupled donor. This work highlights the effectiveness of simple adiabatic inversion techniques for spin control in fluctuating environments.
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In contrast to the rotating B1 field assumed in the simulations, the B1 field in the experiment is linearly polarized. This results in the real B1 field amplitude being a factor 2× larger.
The inversion fidelity was estimated from the control fidelity as , where FC = 57 ± 2% is the angle control fidelity (Ref. 7).