Bose-Einstein condensation in inhomogeneous Josephson arrays
  We show that spatial Bose-Einstein condensation of non-interacting bosons occurs in dimension d < 2 over discrete structures with inhomogeneous topology and with no need of external confining potentials. Josephson junction arrays provide a physical realization of this mechanism. The topological origin of the phenomenon may open the way to the engineering of quantum devices based on Bose-Einstein condensation. The comb array, which embodies all the relevant features of this effect, is studied in detail. 
R. Burioni, D.Cassi, I. Meccoli, M. Rasetti, S. Regina. P. Sodano, A.   Vezzani