Purity as a witness for initial system-environment correlations in   open-system dynamics
  We study the dynamics of a two-level atom interacting with a Lorentzian structured reservoir considering initial system-environment correlations. It is shown that under strong system-reservoir coupling the dynamics of purity can determine whether there are initial correlations between system and environment. Moreover, we investigate the interaction of two two-level atoms with the same reservoir. In this case, we show that besides determining if there are initial system-environment correlations, the dynamics of the purity of the atomic system allows the identification of the distinct correlated initial states. In addition, the dynamics of quantum and classical correlations is analyzed. 
D. Z. Rossatto, T. Werlang, L. K. Castelano, C. J. Villas-Boas, F. F.   Fanchini
quant-ph