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Journal Article

Channel discord and distortion


Zhang,  Wei-Wei
Marquardt Division, Max Planck Institute for the Science of Light, Max Planck Society;
Institute for Theoretical Physics II, FAU;
Centre for Engineered Quantum Systems, School of Physics, The University of Sydney;

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Zhang, W.-W., Sanders, Y. R., & Sanders, B. C. (2021). Channel discord and distortion. New Journal of Physics, (23): 083025. doi:10.1088/1367-2630/ac180a.

Cite as: https://hdl.handle.net/21.11116/0000-0009-73A1-F
Discord, originally notable as a signature of bipartite quantum correlation, in fact can be nonzero
classically, i.e. arising from noisy measurements by one of the two parties. Here we redefine
classical discord to quantify channel distortion, in contrast to the previous restriction of classical
discord to a state, and we then show a monotonic relationship between classical (channel) discord
and channel distortion. We show that classical discord is equivalent to (doubly stochastic) channel
distortion by numerically discovering a monotonic relation between discord and total-variation
distance for a bipartite protocol with one party having a noiseless channel and the other party
having a noisy channel. Our numerical method includes randomly generating doubly stochastic
matrices for noisy channels and averaging over a uniform measure of input messages. Connecting
discord with distortion establishes discord as a signature of classical, not quantum, channel