Entanglement

“Vanishing Quantum Discord is Necessary and Sufficient for Completely Positive Maps”, Phys. Rev. Lett. 102, 100402 (2009), by A. Shabani and D.A. Lidar. [link] ;  “Erratum: Vanishing Quantum Discord is Necessary and Sufficient for Completely Positive Maps”, Phys. Rev. Lett. 11, 049901 (2016), by A. Shabani and D. A. Lidar. [link]