Storing quantum information for 30 seconds in a nanoelectronic device

The spin of an electron or a nucleus in a semiconductor¹ naturally implements the unit of quantum information-the qubit. In addition, because semiconductors are currently used in the electronics industry, developing qubits in semiconductors would be a promising route to realize scalable quantum information devices². The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms³, or charge and spin fluctuations arising from defects in oxides and interfaces⁴. For materials such as silicon, enrichment of the spin-zero ²⁸Si isotope drastically reduces spin-bath decoherence⁵. Experiments on bulk spin ensembles in ²⁸Si crystals have indeed demonstrated extraordinary coherence times^6-8. However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here, we present the coherent operation of individual ³¹P electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered ²⁸Si substrate. The ³¹P nuclear spin sets the new benchmark coherence time (>30 s with Carr-Purcell-Meiboom-Gill (CPMG) sequence) of any single qubit in the solid state and reaches >99.99% control fidelity. The electron spin CPMG coherence time exceeds 0.5 s, and detailed noise spectroscopy⁹ indicates that-contrary to widespread belief-it is not limited by the proximity to an interface. Instead, decoherence is probably dominated by thermal and magnetic noise external to the device, and is thus amenable to further improvement.