Abstract
Silicon has many attractive properties for quantum computing, and the quantum-dot architecture is appealing because of its controllability and scalability. However, the multiple valleys in the silicon conduction band are potentially a serious source of decoherence for spin-based quantum-dot qubits. Only when a large energy splits these valleys do we obtain well-defined and long-lived spin states appropriate for quantum computing. Here, we show that the small valley splittings observed in previous experiments on Si–SiGe heterostructures result from atomic steps at the quantum-well interface. Lateral confinement in a quantum point contact limits the electron wavefunctions to several steps, and enhances the valley splitting substantially, up to 1.5 meV. The combination of electrostatic and magnetic confinement produces a valley splitting larger than the spin splitting, which is controllable over a wide range. These results improve the outlook for realizing spin qubits with long coherence times in silicon-based devices.
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Acknowledgements
We gratefully acknowledge conversations with R. Blick. This work was supported by NSA/LPS under ARO contract number W911NF-04-1-0389, and by the National Science Foundation through the ITR programme (DMR-0325634) and the EMT programme (CCF-0523675).
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J.C. and P.M. provided the samples. S.G., K.S., L.M., J.T., and L.K. carried out the fabrication and measurements. M.F., C.T., R.J. and S.C. did the theoretical work. S.G., K.S., L.M., M.F., S.C. and M.E. analysed the data. M.F., R.J., D.W., S.C., M.F. and M.E. planned the project. M.F., K.S., S.C. and M.E. prepared the manuscript.
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Goswami, S., Slinker, K., Friesen, M. et al. Controllable valley splitting in silicon quantum devices. Nature Phys 3, 41–45 (2007). https://doi.org/10.1038/nphys475
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DOI: https://doi.org/10.1038/nphys475
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