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Discord as a Consumable Resource


Correlations lie at the heart of our capacity to manipulate information. The fewer the constraints on the correlations we can exploit, the greater our capacity to manipulate information in ways we desire. The rapid development of quantum information science is a testament to this observation. Quantum systems may be so correlated that they are `entangled', such that each of its subsystems possesses no local reality. Exploitation of such uniquely quantum correlations has led to many remarkable protocols that would otherwise be either impossible or in feasible. However, the absence of entanglement does not eliminate all signatures of quantum behaviour. Coherent quantum interactions between separable systems that result in negligible entanglement could still lead to exponential speed-ups in computation. The potential presence of discord within such protocols motivated speculation that discord might prove a better quantifier of the `quantum resource' that coherent interactions exploit to deliver a `quantum advantage'.

In this presentation, I will give a brief tutorial of quantum discord. I then introduce and demonstrate an operational method to use discord as a physical resource. I show 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'. I will outline recent experiments done at the Australian National University and the University of Queensland, where we experimentally encoded information within the discordant correlations separable states. The amount of extra information recovered by coherent interaction is quantified and directly linked with the discord consumed during encoding. I survey the potential applications of this phenomena, in both certification of entangling operations, and protecting the benefits of entanglement in entanglement breaking noise.

Nature Physics 8, 671-675 (2012)
Nature Photonics 6, 724-725 (2012)
arXiv preprint arXiv:1301.7110 (2013)
arXiv preprint arXiv:1312.3332 (2013)