Extremal properties of conditional entropy and quantum discord for XXZ, symmetric quantum states

For the XXZ subclass of symmetric two-qubit X states, we study the behavior of quantum conditional entropy Scond as a function of measurement angle θ ∈ [0, π/2]. Numerical calculations show that the function Scond(θ) for X states can have at most one local extremum in the open interval from zero to π/2 (unimodality property). If the extremum is a minimum… CONTINUE READING