  We address the evolution of entanglement in bimodal continuous variable
quantum systems interacting with two independent structured reservoirs. We
derive an analytic expression for the entanglement of formation without
performing the Markov and the secular approximations and study in details the
entanglement dynamics for various types of structured reservoirs and for
different reservoir temperatures, assuming the two modes initially excited in a
twin-beam state. Our analytic solution allows us to identify three dynamical
regimes characterized by different behaviors of the entanglement: the
entanglement sudden death, the non-Markovian revival and the non-secular
revival regimes. Remarkably, we find that, contrarily to the Markovian case,
the short-time system-reservoir correlations in some cases destroy quickly the
initial entanglement even at zero temperature.
