Abstract
Qubits, the quantum mechanical bits required for quantum computing, must retain their quantum states for times long enough to allow the information contained in them to be processed. In many types of electron-spin qubits, the primary source of information loss is decoherence due to the interaction with nuclear spins of the host lattice. For electrons in gate-defined GaAs quantum dots, spin-echo measurements have revealed coherence times of about 1 μs at magnetic fields below 100 mT (refs 1, 2). Here, we show that coherence in such devices can survive much longer, and provide a detailed understanding of the measured nuclear-spin-induced decoherence. At fields above a few hundred millitesla, the coherence time measured using a single-pulse spin echo is 30 μs. At lower fields, the echo first collapses, but then revives at times determined by the relative Larmor precession of different nuclear species. This behaviour was recently predicted3,4, and can, as we show, be quantitatively accounted for by a semiclassical model for the dynamics of electron and nuclear spins. Using a multiple-pulse Carr–Purcell–Meiboom–Gillecho sequence, the decoherence time can be extended to more than 200 μs, an improvement by two orders of magnitude compared with previous measurements1,2,5.
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Acknowledgements
We thank D. J. Reilly for advice on implementing the radiofrequency readout system and J. R. Maze for discussions. We acknowledge financial support from ARO/IARPA, the Department of Defense and the National Science Foundation under award number 0653336. I.N. and M.R. were supported by NSF grant DMR-0906475. This work was carried out in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765.
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Electron-beam lithography and molecular-beam-epitaxy growth were carried out by D.M. and V.U., respectively. H.B., S.F. and A.Y. fabricated the sample, planned and executed the experiment and analysed the data. I.N., M.R., H.B. and A.Y. developed the theoretical model. H.B., S.F., I.N., M.R. and A.Y. wrote the paper.
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Bluhm, H., Foletti, S., Neder, I. et al. Dephasing time of GaAs electron-spin qubits coupled to a nuclear bath exceeding 200 μs. Nature Phys 7, 109–113 (2011). https://doi.org/10.1038/nphys1856
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DOI: https://doi.org/10.1038/nphys1856
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