Topological photon pairs in a superconducting quantum metamaterial

TL;DR

This paper demonstrates the experimental realization of a topological quantum metamaterial using superconducting qubits, revealing topological photon states, bound photon pairs, and interaction-induced localization.

Contribution

It introduces a superconducting qubit array as a topologically nontrivial quantum metamaterial with observable topological states and photon interactions.

Findings

Observation of single-photon topological states

Detection of exotic bound photon pairs

Identification of interaction-induced localization

Abstract

Recent discoveries in topological physics hold a promise for disorder-robust quantum systems and technologies. Topological states provide the crucial ingredient of such systems featuring increased robustness to disorder and imperfections. Here, we use an array of superconducting qubits to engineer a one-dimensional topologically nontrivial quantum metamaterial. By performing microwave spectroscopy of the fabricated array, we experimentally observe the spectrum of elementary excitations. We find not only the single-photon topological states but also the bands of exotic bound photon pairs arising due to the inherent anharmonicity of qubits. Furthermore, we detect the signatures of the two-photon bound edge-localized state which hints towards interaction-induced localization in our system. Our work demonstrates an experimental implementation of the topological model with attractive photon-photon interaction in a quantum metamaterial.