Naimark-Sacker Bifurcations in Linearly Coupled Quadratic Maps
  We report exact analytical expressions locating the $0\to1$, $1\to2$ and $2\to4$ bifurcation curves for a prototypical system of two linearly coupled quadratic maps. Of interest is the precise location of the parameter sets where Naimark-Sacker bifurcations occur, starting from a non-diagonal period-2 orbit. This result is the key to understand the onset of synchronization in networks of quadratic maps. 
Paulo C. Rech, Marcus W. Beims and Jason A.C. Gallas