Single-atom spin qubits in silicon
The idea of using the spin of a single donor atom in silicon to encode quantum information goes back to the Kane proposal  in 1998. The proposal was motivated by two observations: (i) Silicon is one of the most promising materials to host spin qubits in solid state, owing to the very weak spin-orbit coupling, and to the possibility to eliminate decoherence from nuclear spins by isotopic purification; (ii) A trillion-dollar worth industry already exists, that has developed extraordinary tools to manufacture silicon nanoscale devices in a reliable and cost-effective way.
The proposal appeared ambitious, visionary but very challenging at the time, because it relied upon the non-trivial assumption that the progress in the fabrication of classical silicon devices could be harnessed to pursue quantum information goals. Indeed, over a decade of intense efforts has been necessary before the first breakthroughs in silicon quantum technologies could be demonstrated.
I will present the first experimental demonstration of a qubit based on a single phosphorus atom in silicon. The atom is coupled to a silicon Single-Electron Transistor, and the whole device is fabricated retaining standard CMOS technologies such as ion implantation  and metal gates fabricated on top of high-quality silicon oxide .
In a single-atom device, we have demonstrated single-shot readout  and coherent control  of the donor electron spin, as well and the spins of the 31P nucleus and of a strongly-coupled 29Si nucleus. All three qubits exhibit excellent coherence and high-fidelity readability, with the nuclear ones being accessible through a quantum nondemolition measurement.
These results represent major milestones in the search for a scalable and coherent quantum computer platform, and confirm the vision of silicon as the choice material for both quantum and classical technologies.
 B. E. Kane, Nature 393, 133 (1998).
 D. N. Jamieson et al., Appl. Phys. Lett. 86, 202101 (2005).
 A. Morello et al., Phys. Rev. B 80, 081307(R) (2009).
 A. Morello et al., Nature 467, 687 (2010).
 J. J. Pla et al., Nature 489, 541 (2012).
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