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Experimental signature of programmable quantum annealing

Nature Communications volume 4, Article number: 2067 (2013) | Download Citation

Abstract

Quantum annealing is a general strategy for solving difficult optimization problems with the aid of quantum adiabatic evolution. Both analytical and numerical evidence suggests that under idealized, closed system conditions, quantum annealing can outperform classical thermalization-based algorithms such as simulated annealing. Current engineered quantum annealing devices have a decoherence timescale which is orders of magnitude shorter than the adiabatic evolution time. Do they effectively perform classical thermalization when coupled to a decohering thermal environment? Here we present an experimental signature which is consistent with quantum annealing, and at the same time inconsistent with classical thermalization. Our experiment uses groups of eight superconducting flux qubits with programmable spin–spin couplings, embedded on a commercially available chip with >100 functional qubits. This suggests that programmable quantum devices, scalable with current superconducting technology, implement quantum annealing with a surprising robustness against noise and imperfections.

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Acknowledgements

We thank M.H.S. Amin, T. Lanting, M.C. Thom, J. Preskill, T. Rønnow and M. Troyer for useful discussions. We particularly thank M.H.S. Amin for discussions that inspired our choice of the Ising Hamiltonian. This research was supported by the Lockheed Martin Corporation. S.B. and D.A.L. acknowledge support under ARO grant number W911NF-12-1-0523. D.A.L. was further supported by the National Science Foundation under grant number CHM-1037992, and ARO MURI grant W911NF-11-1-0268.

Author information

Affiliations

  1. Information Sciences Institute, University of Southern California, Los Angeles, California 90089, USA

    • Sergio Boixo
    •  & Federico M. Spedalieri
  2. Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA

    • Sergio Boixo
    •  & Daniel A. Lidar
  3. Center for Quantum Information Science & Technology, University of Southern California, Los Angeles, California 90089, USA

    • Sergio Boixo
    • , Tameem Albash
    • , Federico M. Spedalieri
    •  & Daniel A. Lidar
  4. Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, USA

    • Tameem Albash
    • , Nicholas Chancellor
    •  & Daniel A. Lidar
  5. Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA

    • Daniel A. Lidar

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Contributions

S.B. conceived and performed the experiment, and did most of the theoretical analysis of classical thermalization. T.A. performed the open system QA numerical analysis with assistance from N.C. F.S. analysed the possible effects of hardware imperfections on the experimental results. N.C. also performed closed quantum system calculations as well as other supplemental calculations. All authors participated in the interpretation of the experiments and theory development. T.A., D.L. and S.B. carried out the analysis of the decoherence basis. S.B. and D.L. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sergio Boixo.

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    Supplementary Information

    Supplementary Figures S1-S2, Supplementary Methods and Supplementary References

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DOI

https://doi.org/10.1038/ncomms3067

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