Linear response theory of entanglement entropy

Linear response theory (LRT) is a powerful tool for investigating classical and quantum systems when perturbed by some external forces, connecting experimental observables with the correlation functions of system in equilibrium states. On other hand, entanglement entropy (EE), or von Neumann entropy, an important measure non-classical correlations information science. As EE not normal physical observable, developing LRT valuable understanding changes under perturbation. In this work, we present framework entropy. We found that any composite state linear can be quantified special function. Consequently, derive corresponding Kubo formula susceptibility EE, which have same properties as its conventional counterpart. further zero maximally entangled separable states, unique feature dynamics. A numerical verification our analytical results also given based on XX spin chain model. Overall, provides useful EE.