“…An hidden spectrum of the adjacency matrix emerges, for instance, when one analyzes bundled graphs [29] (i.e., those obtained by grafting a fiber graph to every point of a base graph) while, for graphs with constant coordination number (such as the Sierpinski gasket and the ladder graph), the adjacency matrix does not support any hidden spectrum [31]. In the following, we shall analyze the simple paradigmatic case of comb networks showing how the hidden spectrum of the adjacency matrix leads to unusual quantum behaviors such as the emergence of the spatial BEC on the comb's backbone for a Bose gas living on a combshaped optical lattice [30,32] and of the enhanced responses observed for classical combshaped JJNs made of Niobium grains [21,22][see Fig.1]. To better clarify our arguments, we find instructive to compare our results with those obtainable if the same devices were defined on a chain, since the latter is, after all, the simplest graph of euclidean dimension 1.…”