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An addressable quantum dot qubit with fault-tolerant control-fidelity


Exciting progress towards spin-based quantum computing1,2 has recently been made with qubits realized using nitrogen-vacancy centres in diamond and phosphorus atoms in silicon3. For example, long coherence times were made possible by the presence of spin-free isotopes of carbon4 and silicon5. However, despite promising single-atom nanotechnologies6, there remain substantial challenges in coupling such qubits and addressing them individually. Conversely, lithographically defined quantum dots have an exchange coupling that can be precisely engineered1, but strong coupling to noise has severely limited their dephasing times and control fidelities. Here, we combine the best aspects of both spin qubit schemes and demonstrate a gate-addressable quantum dot qubit in isotopically engineered silicon with a control fidelity of 99.6%, obtained via Clifford-based randomized benchmarking and consistent with that required for fault-tolerant quantum computing7,8. This qubit has dephasing time T2* = 120 μs and coherence time T2 = 28 ms, both orders of magnitude larger than in other types of semiconductor qubit. By gate-voltage-tuning the electron g*-factor we can Stark shift the electron spin resonance frequency by more than 3,000 times the 2.4 kHz electron spin resonance linewidth, providing a direct route to large-scale arrays of addressable high-fidelity qubits that are compatible with existing manufacturing technologies.

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Figure 1: Silicon quantum dot qubit with single electron transistor (SET) readout and on-chip microwave spin control.
Figure 2: Electron spin resonance (ESR) and Rabi oscillations.
Figure 3: Qubit coherence.
Figure 4: Control fidelity analysis via randomized benchmarking of Clifford gates.
Figure 5: Gate-voltage tunability of the qubit operation frequency and of the valley splitting.


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The authors thank D. J. Reilly and J. R. Petta for discussions. The authors acknowledge support from the Australian Research Council (CE11E0096), the US Army Research Office (W911NF-13-1-0024) and the NSW Node of the Australian National Fabrication Facility. M.V. acknowledges support from the Netherlands Organization for Scientific Research (NWO) through a Rubicon Grant. The work at Keio has been supported in part by FIRST, the Core-to-Core Program by JSPS, and the Grant-in-Aid for Scientific Research and Project for Developing Innovation Systems by MEXT.

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M.V., J.C.C.H., C.H.Y., A.W.L., B.R., J.P.D. and J.T.M. performed the experiments. M.V. and F.E.H. fabricated the devices. K.M.I. prepared and supplied the 28Si epilayer wafer. M.V., C.H.Y., A.M. and A.S.D. designed the experiments and analysed the results. M.V. and A.S.D. wrote the manuscript, with input from all authors.

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Correspondence to M. Veldhorst or A. S. Dzurak.

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The authors declare no competing financial interests.

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Veldhorst, M., Hwang, J., Yang, C. et al. An addressable quantum dot qubit with fault-tolerant control-fidelity. Nature Nanotech 9, 981–985 (2014).

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