Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment1. The outstanding challenge is to engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here, we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet2, and the spin state is read out in the single-shot mode3. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, a Ramsey decay timescale of 1 μs is observed, almost two orders of magnitude longer than the intrinsic timescales in GaAs quantum dots4,5, whereas gate operation times are comparable to those reported in GaAs6,7,8. The spin echo decay time is ∼40 μs, both with one and four echo pulses, possibly limited by intervalley scattering. These advances strongly improve the prospects for quantum information processing based on quantum dots.
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The authors acknowledge useful discussions with L. Schreiber, J. Prance, G. de Lange, A. Morello, W. Coish, F. Beaudoin and our spin qubit teams, comments by L. DiCarlo and R. Hanson, and experimental assistance from P. Barthelemy, M. Tiggelman and R. Schouten. This work was supported in part by the Army Research Office (ARO) (W911NF-12-0607), the Foundation for Fundamental Research on Matter (FOM) and the European Research Council (ERC). Development and maintenance of the growth facilities used for fabricating samples was supported by the Department of Energy (DOE) (DE-FG02-03ER46028). E.K. was supported by a fellowship from the Nakajima Foundation. This research utilized NSF-supported shared facilities at the University of Wisconsin–Madison.
The authors declare no competing financial interests.
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Kawakami, E., Scarlino, P., Ward, D. et al. Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot. Nature Nanotech 9, 666–670 (2014). https://doi.org/10.1038/nnano.2014.153
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