Measurement-extracted total, classical and quantum correlations

Abstract

Measurements are indispensable tools for extracting information about quantum systems. For a bipartite system, local measurements provide a way to probe its correlations. In this work, we study correlations of a bipartite state from the perspective of local measurements. We introduce measurement-extracted total correlations as the average reduction of quantum mutual information caused by this measurement, and show that it can be decomposed into classical part (called measurement-extracted classical correlations, quantified by the average reduction of the von Neumann entropy of the unmeasured subsystem) and quantum part (called measurement-extracted quantum correlations, quantified by the coherence difference between the bipartite state and the reduced state of the measured subsystem). We investigate their basic properties and reveal the connections between the measurement-extracted correlations and the conventional measurement-independent correlations by rank-1 positive-operator-valued measures. Finally, we evaluate these correlations quantifiers for two-qubit Werner states relative to several prototypical measurements.