A >99.9%-fidelity quantum-dot spin qubit with coherence limited by charge noise

摘要

Recent advances towards spin-based quantum computation have been primarilyfuelled by elaborate isolation from noise sources, such as surrounding nuclearspins and spin-electric susceptibility, to extend spin coherence. In themeanwhile, addressable single-spin and spin-spin manipulations inmultiple-qubit systems will necessitate sizable spin-electric coupling. Givenbackground charge fluctuation in nanostructures, however, its compatibilitywith enhanced coherence should be crucially questioned. Here we realise asingle-electron spin qubit with isotopically-enriched phase coherence time (20microseconds) and fast electrical control speed (up to 30 MHz) mediated byextrinsic spin-electric coupling. Using rapid spin rotations, we reveal thatthe free-evolution dephasing is caused by charge (instead of conventionalmagnetic) noise featured by a 1/f spectrum over seven decades of frequency. Thequbit nevertheless exhibits superior performance with single-qubit gatefidelities exceeding 99.9% on average. Our work strongly suggests thatdesigning artificial spin-electric coupling with account taken of charge noiseis a promising route to large-scale spin-qubit systems having fault-tolerantcontrollability.