Topological and nontopological photonic states in two coupled circuit quantum electrodynamics chains

We investigate the topological and nontopological photonic states induced by the interchain coupling strength in a one-dimensional coupled circuit quantum electrodynamics chains system. In the case of strong coupling strength, we find that the original topologically nontrivial interface states of the system gradually disappear and finally become two nontopological impurity states. Meanwhile, two new topologically nontrivial interface states appear next to the two middle resonators. The processes can be clearly delineated by the energy eigenvalue spectrum and the state distributions of the system. Moreover, we present the phase diagram to illustrate the characteristics of phase transition of the system. Assisted by the lattice-based cavity input-output process, we can measure these photonic states, which are either localized or extended, in the steady state condition. Our scheme would be feasible for experimental implementation of topological and nontopological photonic states with the current physical system.