Letter | Published:

A programmable two-qubit quantum processor in silicon

Nature volume 555, pages 633637 (29 March 2018) | Download Citation

Abstract

Now that it is possible to achieve measurement and control fidelities for individual quantum bits (qubits) above the threshold for fault tolerance, attention is moving towards the difficult task of scaling up the number of physical qubits to the large numbers that are needed for fault-tolerant quantum computing1,2. In this context, quantum-dot-based spin qubits could have substantial advantages over other types of qubit owing to their potential for all-electrical operation and ability to be integrated at high density onto an industrial platform3,4,5. Initialization, readout and single- and two-qubit gates have been demonstrated in various quantum-dot-based qubit representations6,7,8,9. However, as seen with small-scale demonstrations of quantum computers using other types of qubit10,11,12,13, combining these elements leads to challenges related to qubit crosstalk, state leakage, calibration and control hardware. Here we overcome these challenges by using carefully designed control techniques to demonstrate a programmable two-qubit quantum processor in a silicon device that can perform the Deutsch–Josza algorithm and the Grover search algorithm—canonical examples of quantum algorithms that outperform their classical analogues. We characterize the entanglement in our processor by using quantum-state tomography of Bell states, measuring state fidelities of 85–89 per cent and concurrences of 73–82 per cent. These results pave the way for larger-scale quantum computers that use spins confined to quantum dots.

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Acknowledgements

This research was sponsored by the Army Research Office (ARO) under grant numbers W911NF-17-1-0274 and W911NF-12-1-0607. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the ARO or the US Government. The US Government is authorized to reproduce and distribute reprints for government purposes notwithstanding any copyright notation herein. Development and maintenance of the growth facilities used for fabricating samples is supported by DOE (DE-FG02-03ER46028). We acknowledge the use of facilities supported by NSF through the University of Wisconsin-Madison MRSEC (DMR-1121288). E.K. was supported by a fellowship from the Nakajima Foundation. We acknowledge financial support from the Marie Skłodowska-Curie actions—Nanoscale solid-state spin systems in emerging quantum technologies—Spin-NANO, grant agreement number 676108. We acknowledge discussions with S. Dobrovitski, C. Dickel, A. Rol, J. P. Dehollain, Z. Ramlakhan and members of the Vandersypen group, and technical assistance from R. Schouten, R. Vermeulen, M. Tiggelman, M. Ammerlaan, J. Haanstra, R. Roeleveld and O. Benningshof.

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Affiliations

  1. QuTech and the Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands

    • T. F. Watson
    • , S. G. J. Philips
    • , E. Kawakami
    • , P. Scarlino
    • , M. Veldhorst
    •  & L. M. K. Vandersypen
  2. University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

    • D. R. Ward
    • , D. E. Savage
    • , M. G. Lagally
    • , Mark Friesen
    • , S. N. Coppersmith
    •  & M. A. Eriksson

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Contributions

T.F.W. performed the experiment with help from E.K. and P.S., T.F.W. and S.G.J.P. analysed the data, S.G.J.P. performed the simulations of the algorithms, T.F.W., S.G.J.P., E.K., P.S., M.V., M.F., S.N.C., M.A.E. and L.M.K.V. contributed to the interpretation of the data and commented on the manuscript, D.R.W. fabricated the device, D.E.S. and M.G.L. grew the Si/SiGe heterostructure, T.F.W. wrote the manuscript (S.G.J.P. wrote parts of Methods) and L.M.K.V. conceived and supervised the project.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to L. M. K. Vandersypen.

Reviewer Information Nature thanks H. Bluhm and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature25766

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