  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.
