title: Nonzero Classical Discord.
abstract: Quantum discord is the quantitative difference between two alternative expressions for bipartite mutual information, given respectively in terms of two distinct definitions for the conditional entropy. By constructing a stochastic model of shared states, classical discord can be similarly defined, quantifying the presence of some stochasticity in the measurement process. Therefore, discord can generally be understood as a quantification of the system's state disturbance due to local measurements, be it quantum or classical. We establish an operational meaning of classical discord in the context of state merging with noisy measurement and thereby show the quantum-classical separation in terms of a negative conditional entropy.
authors.affiliation: Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.|Institute for Quantum Science and Technology, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Vlad
authors.initials: V
authors.lastname: Gheorghiu
authors.affiliation: Institute for Quantum Science and Technology, University of Calgary, Calgary, Alberta T2N 1N4, Canada.|Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, CEP 13083-859, Campinas, SP, Brazil.
authors.forename: Marcos C
authors.initials: MC
authors.lastname: de Oliveira
authors.affiliation: Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.|Institute for Quantum Science and Technology, University of Calgary, Calgary, Alberta T2N 1N4, Canada.|Program in Quantum Information Science, Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada.
authors.forename: Barry C
authors.initials: BC
authors.lastname: Sanders