Mile Gu, Helen M. Chrzanowski, Syed M. Assad, Thomas Symul, Kavan Modi, Timothy C. Ralph, Vlatko Vedral, Ping Koy Lam
Observations that coherent interactions between non-entangled systems can still exhibit unique quantum behaviour challenged the traditional view that quantum correlations are synonymous with entanglement. In response, quantum discord was proposed to complete the description of all quantum correlations. Nevertheless, explicit protocols that directly exploit discord as a quantum resource have remained elusive. Here, we demonstrate that under certain measurement constraints, discord between bipartite systems directly quantifies a quantum resource that coherent interactions can harness. The inability to access this resource 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 between the states. No entanglement exists at any point of this experiment. Thus we introduce and demonstrate an operational meaning for quantum discord.
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http://arxiv.org/abs/1203.0011
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