How to observe and quantify quantum-discorded states via correlations

Authors :: Hunt, Matthew A.
Lerner, Igor V.
Yurkevich, Igor V.
Gefen, Yuval
Publication Year :: 2019
Abstract: Quantum correlations between parts of a composite system most clearly reveal themselves through entanglement. Designing, maintaining, and controlling entangled systems is very demanding, which raises the stakes for understanding the efficacy of entanglement-free, yet quantum, correlations, exemplified by quantum discord. Discord is defined via conditional mutual entropies of parts of a composite system, and its direct measurement is hardly possible even via full tomographic characterization of the system state. Here we design a simple protocol to detect and quantify quantum discord in an unentangled bipartite system. Our protocol relies on a characteristic of discord that can be extracted from repeated direct measurements of certain correlations between subsystems of the bipartite system. The proposed protocol opens a way of extending experimental studies of discord to electronic systems but can also be implemented in quantum-optical systems.<br />Comment: 10 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:1901.11514