Saleh Rahimi-Keshari, Carlton M. Caves, Timothy C. Ralph
We introduce a measurement-based method for verifying quantum discord of any bipartite quantum system. We show that if the reduced states of one subsystem, conditioned to all outcomes of an informationally complete POVM (IC-POVM) performed on the other subsystem, commute with one another, there is no quantum discord from the first subsystem to the second. In particular, this method enables us to verify quantum discord for continuous-variable systems, as IC-POVMs are readily available from homodyne and heterodyne measurements. Using this method, we show that the only Gaussian states with zero discord are product states; hence Gaussian states with Gaussian discord have nonzero quantum discord.
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http://arxiv.org/abs/1209.2221
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