Quantum computers have the potential to dramatically reduce computing time for problems such as factoring  and database searching . In particular a silicon-based quantum computer  shows promise for its potential to scale to a large number of qubits and for its compatibility with standard CMOS processing.
Our group has designed a fabrication strategy for the realisation of a scaleable quantum computer based in silicon using a combination of scanning probe microscopy for single qubit placement and silicon molecular beam epitaxy to encapsulate the qubit array . In order to achieve this goal we have demonstrated the following key steps: we have been able to incorporate single P atoms as the qubits in silicon with atomic precision ; we have been able to minimise P segregation and diffusion during Si encapsulation  and we have imaged the array of buried P atoms using scanning tunneling microscopy to prove that the array remains intact after the encapsulation stage. Recently we have been able to fabricate a robust electrical device in silicon using the scanning tunneling microscope to lithographically pattern the dopants  and have demonstrated that this device can be contacted and measured outside the ultra-high vacuum environment.
We highlight the importance of our results for the fabrication of a Si-based quantum computer and discuss the final stages of the fabrication process required to realize a functional device, including the formation of an electrical isolation barrier and the alignment of surface metal electrodes to the buried P atom array.
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- http://www.qcaustralia.org/bio/staff_simmons.htm - web-site of presenting author