Abstract
Silicon quantum dots are one of the most promising candidates for practical quantum computers because of their scalability and compatibility with the well-established complementary metal-oxide-semiconductor technology. However, the coherence time is limited in industry-standard natural silicon because of the 29Si isotopes, which have non-zero nuclear spin. Here, we protect an isotopically natural silicon metal-oxide-semiconductor (Si-MOS) quantum dot spin qubit from environmental noise via electron spin resonance with a phase-modulated microwave (MW) drive. This concatenated continuous drive (CCD) method extends the decay time of Rabi oscillations from 1.2 μs to over 200 μs. Furthermore, we define a protected qubit basis and propose robust gate operations. We find the coherence time measured by Ramsey sequence is improved from 143 ns to 40.7 μs compared to that of the bare spin qubit. The single qubit gate fidelity measured with randomized benchmarking is improved from 95% to 99%, underscoring the effectiveness of the CCD method. The method shows promise for improving control fidelity of noisy qubits, overcoming the qubit variability for global control, and maintaining qubit coherence while idling.
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Acknowledgements
This work was supported by JST Moonshot R&D Grant Number JPMJMS2065, Grants-in-Aid for Scientific Research grant numbers JP23H05455 and JP23K17327, and JST PRESTO Grant Number JPMJPR21BA.
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T.Ku. performed the experiment and analyzed the data. T.Ku., T.U., A.J.R., N.M., R.M., T.N, J.Y., T.Ko., S.S., D.H. and R.T. discussed the results. T.Ku., T.U. and N.K contributed to the measurement setup. N.L., I.Y., T.M., D.H., and R.T. designed and fabricated the device. T.Ku., T.U,. and A.J.R. performed calculations. T.Ku. and A.J.R. wrote the manuscript with input from all co-authors. H.M. supervised the project.
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Kuno, T., Utsugi, T., Ramsay, A.J. et al. Robust spin-qubit control in a natural Si-MOS quantum dot using phase modulation. npj Quantum Inf (2026). https://doi.org/10.1038/s41534-026-01185-3
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DOI: https://doi.org/10.1038/s41534-026-01185-3
