Observing the quantum topology of light

Topological photonics provides a powerful platform to explore topological physics beyond traditional electronic materials and shows promising applications in light transport and lasers. Classical degrees of freedom are routinely used to construct topological light modes in real or synthetic dimensions. Beyond the classical topology, the inherent quantum nature of light provides a wealth of fundamentally distinct topological states. Here we implement experiments on topological states of quantized light in a superconducting circuit, with which one- and two-dimensional Fock-state lattices are constructed. We realize rich topological physics including topological zero-energy states of the Su-Schrieffer-Heeger model, strain-induced pseudo-Landau levels, valley Hall effect, and Haldane chiral edge currents. Our study extends the topological states of light to the quantum regime, bridging topological phases of condensed-matter physics with circuit quantum electrodynamics, and offers a freedom in controlling the quantum states of multiple resonators. Description Topological quantum photonics Exploiting the topological properties of materials is expected to provide a route to developing robust platforms for transport and communication systems that are immune to defects. In optics, the demonstration of topological behavior has been confined mainly to classical light. Deng et al. introduce a superconducting chip–based platform consisting of a single qubit coupled to a number of resonators. By controlling the photon population in each resonator and the coupling strength, the authors were able to realize several important models in topological physics. The approach bridges the gap between topological states of classical and quantum origin. —ISO A superconducting-based circuit allows the coherent control of topological states of quantized light.