  We show by general arguments that networks whose density of states contains
few highly degenerate eigenvalues result in inefficient performances of
continuous-time quantum walks (CTQW) over these networks, while systems whose
eigenvalues all have the same degeneracy lead to very efficient transport. We
exemplify our results by considering CTQW and, for comparison, its classical
counterpart, continuous-time random walks, over simple structures, whose
eigenvalues and eigenstates can be calculated analytically. Extensions to more
complicated, hyper-branched networks are discussed.
