Fidelity and concurrence of conjugated states

Abstract

We prove some properties of fidelity (transition probability) and concurrence, the latter defined by a straightforward extension of Wootters' notation. Choose a conjugation and consider the dependence of fidelity or of concurrence on conjugated pairs of density operator. These functions turn out to be concave or convex roofs. Optimal decompositions are constructed. Some applications to two and tripartite systems illustrate the general theorems.