  We theoretically predict the formation of two-photon bound states in a
two-dimensional waveguide network hosting a lattice of two-level atoms. The
properties of these bound pairs and the exclusive domains of the parameter
space where they emerge due to the interplay between the on-site photon
blockade and peculiar shape of polariton dispersion resulting from the
long-range radiative couplings between the qubits are investigated in detail.
In addition, we analyze the effect of the finite-size system on localization
characteristics of these excitations.
