Localization and delocalization in networks with varied connectivity

Abstract

We study the phenomenon of localization and delocalization in a circuit-QED network with connectivity varying from finite-range coupling to all-to-all coupling. We find a fascinating interplay between interactions and connectivity. In particular, we consider (i) harmonic, (ii) Jaynes-Cummings, and (iii) Bose-Hubbard networks. We start with the initial condition where one of the nodes in the network is populated and then let it evolve in time. The time dynamics and steady state characterize the features of localization (self-trapping) in these large-scale networks. For the case of harmonic networks, exact analytical results are obtained, and we demonstrate that all-to-all connection shows self-trapping whereas the finite-ranged connectivity shows delocalization. The interacting cases (Jaynes-Cummings and Bose-Hubbard networks) are investigated both via exact quantum dynamics and via a semiclassical approach. We obtain an interesting phase diagram when one varies the range of connectivity and the strength of the interaction. We investigate the consequence of imperfections in the cavity or qubit and the role of inevitable disorder. Our results are relevant especially given recent experimental progress in engineering systems with long-range connectivity.