Relative entropy as a measure of entanglement for Gaussian states

In this paper, we derive an explicit analytic expression of therelative entropy between two general Gaussian states. In therestriction of the set for Gaussian states and with the help ofrelative entropy formula and Peres--Simon separability criterion,one can conveniently obtain the relative entropy entanglement forGaussian states. As an example, the relative entanglement for atwo-mode squeezed thermal state has been obtained.