Witnessing the quantum discord of all the unknown states [article]

Sixia Yu, Chengjie Zhang, Qing Chen, C.H.Oh
2011 arXiv   pre-print
Like entanglement, quantum discord quantifies the quantum correlations. Unlike entanglement, whose detection is extremely difficult, the quantum discord of an arbitrary bipartite state allows itself to be detected perfectly by a single observable, the quantum discord witness. In particular, we report a single observable whose expectation value provides a necessary and sufficient condition for the vanishing quantum discord of an arbitrary bipartite unknown state with four copies. A quantum
more » ... t is designed to measure the quantum discord witness by using only local qubit-measurements.
arXiv:1102.4710v1 fatcat:nqffzwgmzzazvb6jmr6pjxvv6a