Topological excitations and bound photon pairs in a superconducting quantum metamaterial

Topological photonics enables resilient routing and localization of light. Of special interest are topological states of quantum light promising disorder-robust quantum correlations. Here, the authors design and fabricate a one-dimensional dimerized array of superconducting qubits. Performing microwave spectroscopy of this fabricated quantum metamaterial, they observe not only single-photon topological states but also the bands of exotic bound photon pairs mediated by the anharmonicity of qubits. They also discuss the two-photon bound edge-localized state and analyze the robustness of photon-photon correlations.