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arXiv · 1208.5605

Discording power of quantum evolutions

F. Galve·F. Plastina·M. G. A. Paris·R. Zambrini
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Abstract

We introduce the discording power of a unitary transformation, which assesses its capability to produce quantum discord, and analyze in detail the generation of discord by relevant classes of two-qubit gates. Our measure is based on the Cartan decomposition of two-qubit unitaries and on evaluating the maximum discord achievable by a unitary upon acting on classical-classical states at fixed purity. We found that there exist gates which are perfect discorders for any value of purity, and that they belong to a class of operators that includes the $\sqrt{SWAP}. Other gates, even those universal for quantum computation, do not posses the same property: the CNOT, for example, is a perfect discorder only for states with low or unit purity, but not for intermediate values. The discording power of a two-qubit unitary also provides a generalization of the corresponding measure defined for entanglement to any value of the purity.

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F. Galve, F. Plastina, M. G. A. Paris, R. Zambrini. 2012-12-10. Discording power of quantum evolutions. https://doi.org/10.1103/physrevlett.110.010501

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