Nonzero Classical Discord

TL;DR

This paper introduces a classical analogue of quantum discord, quantifying measurement disturbance in stochastic models, and demonstrates its operational significance in state merging with noisy measurements, highlighting quantum-classical differences.

Contribution

It defines classical discord through stochastic models and establishes its operational meaning in state merging, illustrating quantum-classical distinctions.

Findings

Classical discord quantifies measurement-induced stochasticity.

Operational meaning is established in state merging with noise.

Demonstrates quantum-classical separation via negative conditional entropy.

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.