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Observing the operational significance of discord consumption

Nature Physics volume 8, pages 671–675 (2012)Cite this article

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Abstract

Coherent interactions that generate negligible entanglement can still exhibit unique quantum behaviour. This observation has motivated a search beyond entanglement for a complete description of all quantum correlations. Quantum discord is a promising candidate. Here, we demonstrate that under certain measurement constraints, discord between bipartite systems can be consumed to encode information that can only be accessed by coherent quantum interactions. The inability to access this information by any other means allows us to use discord to directly quantify this ‘quantum advantage’. We experimentally encode information within the discordant correlations of two separable Gaussian states. The amount of extra information recovered by coherent interaction is quantified and directly linked with the discord consumed during encoding. No entanglement exists at any point of this experiment. Thus we introduce and demonstrate an operational method to use discord as a physical resource.

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Figure 1: Experimental implementation of the discord consumption protocol in continuous variables.
Figure 2: Plot of Bob’s knowledge of the encoded signal for bipartite resource states with varying discording noise and fixed encoding variance Vs.
Figure 3: Plot of quantum advantage for a fixed resource state (with V = 10.0±0.1) with varying strength of the the encoded signal, Vs.

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Acknowledgements

We thank C. Weedbrook, J. Thompson, N. Walk and H. Wiseman for helpful discussions. The research is supported by the National Research Foundation and Ministry of Education in Singapore (M.G., K.M. and V.V.), the John Templeton Foundation (K.M. and V.V.), and the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (Project number CE110001027). (H.C., S.M.A., T.S., T.C.R. and P.K.L.).

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Author notes

  1. Mile Gu and Helen M. Chrzanowski: These authors contributed equally to this work

Authors and Affiliations

  1. Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore

    Mile Gu, Kavan Modi & Vlatko Vedral

  2. Department of Quantum Science, Centre for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 0200, Australia

    Helen M. Chrzanowski, Syed M. Assad, Thomas Symul & Ping Koy Lam

  3. Department of Physics, University of Oxford, Clarendon Laboratory, Oxford, OX1 3PU, UK

    Kavan Modi & Vlatko Vedral

  4. Department of Physics, Centre for Quantum Computation and Communication Technology, University of Queensland, St Lucia 4072, Australia

    Timothy C. Ralph

  5. Department of Physics, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore

    Vlatko Vedral

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  1. Mile Gu
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Contributions

M.G. V.V. and T.C.R. conceived the idea. M.G. and K.M. formalized the theory. P.K.L., M.G., T.S., S.M.A. and H.M.C. conceived the experiment. H.M.C. and S.M.A. conducted the experiment and analysed the data. S.M.A. and H.M.C. developed the experimental model. M.G., H.M.C, T.S. and S.M.A. drafted the manuscript. P.K.L, T.S. and V.V. planned and supervised the project. All authors discussed the results and commented on the manuscript at all stages.

Corresponding authors

Correspondence to Mile Gu or Ping Koy Lam.

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The authors declare no competing financial interests.

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Gu, M., Chrzanowski, H., Assad, S. et al. Observing the operational significance of discord consumption. Nature Phys 8, 671–675 (2012). https://doi.org/10.1038/nphys2376

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