A phosphorus (31P) donor in silicon is, almost literally, the equivalent of a hydrogen atom in vacuum. It possesses electron and nuclear spins 1/2 which act as natural qubits, and the host material can be isotopically purified to be almost perfectly free of other spin species, ensuring extraordinary coherence times.
I will present the current state-of-the-art in silicon quantum information technologies. Both the electron  and the nuclear  spin of a single 31P atom can be read out in single-shot  with high fidelity, through a nanoelectronic device compatible with standard semiconductor fabrication. High-frequency microwave  pulses can be used to prepare arbitrary quantum states of the spin qubits, with fidelity in excess of 99%. Our latest experiment on the 31P nucleus has established the record coherence time (35 seconds) for any single qubit in solid state , by making use of an isotopically enriched 28Si epilayer.
Finally, I will discuss current efforts to scale up the system to multi-qubit quantum logic operations. We have demonstrated on a single-atom device the long-sought “A-gate” electrical control of a spin in a continuous microwave field , which greatly facilitates addressing multiple qubits. We have observed the singlet/triplet states of a strongly-coupled donor pair , proposed a new scheme for entangling two-qubit logic gates  that does not require atomically precise placement of the 31P donors, and we are exploring cavity-mediated long-distance spin coupling.
These results show that silicon – the material underpinning the whole modern computing era – can be successfully adapted to host quantum information hardware.
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