Discriminating Strength: a bona fide measure of non-classical correlations

Abstract

A new measure of non-classical correlations is introduced and characterized. It tests the ability of using a state {\rho} of a composite system AB as a probe for a quantum illumination task [e.g. see S. Lloyd, Science 321, 1463 (2008)], in which one is asked to remotely discriminate among the two following scenarios: i) either nothing happens to the probe, or ii) the subsystem A is transformed via a local unitary R_A whose properties are partially unspecified when producing {\rho}. This new measure can be seen as the discrete version of the recently introduced Intereferometric Power measure [G. Girolami et al. e-print arXiv:1309.1472 (2013)] and, at least for the case in which A is a qubit, it is shown to coincide (up to an irrelevant scaling factor) with the Local Quantum Uncertainty measure of D. Girolami, T. Tufarelli, and G. Adesso, Phys. Rev. Lett. 110, 240402 (2013). Analytical expressions are derived which allow us to formally prove that, within the set of separable configurations, the maximum value of our non-classicality measure is achieved over the set of quantum-classical states (i.e. states {\rho} which admit a statistical unravelling where each element of the associated ensemble is distinguishable via local measures on B).