Linking Quantum Discord to Entanglement in a Measurement

TL;DR

This paper demonstrates that von Neumann measurements on parts of a quantum system with nonzero discord generate entanglement, linking quantum discord to entanglement creation and providing a unified view of quantum correlations.

Contribution

It establishes a direct quantitative relationship between quantum discord and the minimal distillable entanglement created during measurement, extending to multipartite systems.

Findings

Quantum discord equals the minimal partial distillable entanglement lost.

Measurement on a subsystem with nonzero discord creates entanglement with the apparatus.

Any entanglement measure can be associated with a quantum correlation measure.

Abstract

We show that a von Neumann measurement on a part of a composite quantum system unavoidably creates distillable entanglement between the measurement apparatus and the system if the state has nonzero quantum discord. The minimal distillable entanglement is equal to the one-way information deficit. The quantum discord is shown to be equal to the minimal partial distillable entanglement that is the part of entanglement which is lost, when we ignore the subsystem which is not measured. We then show that any entanglement measure corresponds to some measure of quantum correlations. This powerful correspondence also yields necessary properties for quantum correlations. We generalize the results to multipartite measurements on a part of the system and on the total system.