Observing the operational significance of discord consumption


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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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.).

Author information

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.

Correspondence to Mile Gu or Ping Koy Lam.

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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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