Entropic and information inequality for nonlinearly transformed two-qubit X-states

TL;DR

This paper derives explicit entropic and information inequalities for two-qubit X-states affected by nonlinear channels, analyzing their impact on quantum information measures and extending previous Werner state results.

Contribution

It provides explicit formulas for entropic and information inequalities for nonlinear transformations of two-qubit X-states, generalizing earlier Werner state findings.

Findings

Von Neumann information increases after nonlinear channel action

Subadditivity and nonnegativity conditions are studied for initial and transformed states

Results extend previous Werner state analysis to general X-states

Abstract

The entropic and information inequalities for two qubit X-states transformed by the nonlinear channels are given in explicit form. The subadditivity condition and nonnegativity of von Neumann quantum information are studied for both initial X-state and the state after action of the nonlinear channel. Partial case of Werner state is considered in detail. We shown that the von Neumann information increases due to action of the nonlinear channel. We generalize the results obtained for Werner state in our earlier article [J. Russ. Laser Res., \textbf{35}, iss. 3 (2014)] to the case of X-state of two qubit system. We study the influence of nonlinear channel acting on X-state of two qubit system onto von Neumann mutual information.