The discrimination problem for two ground states or two thermal states of the quantum Ising model

We address the one-dimensional quantum Ising model as an example of a system exhibiting criticality and study in some details the discrimination problem for pairs of states corresponding to different values of the coupling constant. We evaluate the error probability for single-copy discrimination, the Chernoff bound for n-copy discrimination in the asymptotic limit, and the Chernoff metric for the discrimination of infinitesimally close states. We point out scaling properties of the above quantities, and derive the external field optimizing state discrimination for short chains as well as in the thermodynamical limit, thus assessing criticality as a resource for quantum discrimination in many-body systems.