Natural criteria of quantum correlations of two coupled oscillators   interacting with baths
  We consider a problem of description of quantum correlations and dispersions of subsystems of complex open systems. Based on our previous results we proposed a method to evaluate pure quantum contributions from total statistical characteristics of two coupled oscillators interacting with thermal reservoirs. The natural way to extract pure quantum characteristic of the system under study is a calculation of difference between the total value and its pure classical part. A numerical study of temporal behavior of quantum variances and covariances from given initial states up to states in the infinite time limit is given using the proposed method. It is shown that at comparatively high temperatures the steady state total variances are almost classical, because their pure quantum parts tend to zero in this regime. Otherwise, at comparatively low temperatures, the pure quantum parts of variances are not zeroing in steady states manifesting a finite contribution to total values. The same is true for the covariance. The larger the temperature, the lower is the quantum contribution to the total covariance. As well as entanglement measures, quantum discord, the pure quantum contributions in the covariance matrix elements are important characteristics of the temporal dynamics of complex quantum systems. 
Illarion Dorofeyev
quant-ph