The presence of quantum correlations result in non-vanishing ergotropic gap

The paradigm of extracting work from isolated quantum system through a cyclic Hamiltonian process is a topic of immense research interest. The optimal work extracted under such process is termed as ergotropy [Europhys. Lett., 67 (4), 565(2004)]. Here, in a multi-party scenario we consider only a class of such cyclic processes that can be implemented locally, giving rise to the concept of local ergotropy. Eventually, presence of quantum correlations result in a non-vanishing thermodynamic quantity called ergotropic gap, measured by the difference between the global and local ergotropy. However the converse does not hold in general, i.e. its nonzero value does not necessarily imply presence of quantum correlations. For arbitrary multi-party states we quantify this gap. We also evaluate the difference between maximum global and local extractable work for arbitrary states when the system is no longer isolated but put in contact with a baths of same local temperature.Comment: Accepted in Phys. Rev.

Optimal quantum violation of Clauser-Horne-Shimony-Holt like steering inequality

We study a recently proposed Einstein-Podolsky-Rosen steering inequality [arXiv- 1412.8178 (2014)]. Analogous to Clauser-Horne-Shimony-Holt (CHSH) inequality for Bell nonlocality, in the simplest scenario, i.e., 2 parties, 2 measurements per party and 2 outcomes per measurement, this newly proposed inequality has been proved to be necessary and sufficient for steering. In this article, using an equivalence between measurement incompatibility (non joint measurability) and steering, we find the optimal violation amount of this inequality in quantum theory. Interestingly, the optimal violation amount matches with optimal quantum violation of CHSH inequality, i.e., Cirel'son quantity. We further study the optimal violation of this inequality for different bipartite quantum states. To our surprise we find that optimal violation amount is different for different $2$-qubit pure entangled states, which is not the case for all other existing steering inequalities.Comment: 5.5 pages, 2 figures, Comments are welcom