Flat band resonances in synthetic Floquet topological photonic lattices

Flat bands in topological insulators are important in the study of fundamental phenomena such as compact localized states, superconductivity, the fractional quantum Hall effect, as well as for applications such as light storage, sensing and enhanced nonlinear interactions. Here we show that by introducing a synthetic time-like dimension to a static Lieb lattice, the resulting Floquet-Lieb insulator exhibits a host of novel effects such as topological flat bands, Aharonov-Anandan caging, and all-bands-flat systems. We realized Floquet-Lieb insulators using coupled microring resonators on a silicon photonic platform and experimentally observed the flat band resonances and their compact localized states. These results suggest that these synthetic Floquet microring lattices provide a versatile platform for studying the physics and applications of flat bands.