Realization of robust boundary modes and non-contractible loop states in photonic Kagome lattices

TL;DR

This paper demonstrates the experimental realization of topologically protected boundary and non-contractible loop states in photonic Kagome lattices using a Corbino-geometry setup, revealing robust boundary modes and localized states due to real-space topology.

Contribution

It introduces a novel photonic Kagome lattice design in Corbino-geometry, enabling direct observation of non-contractible loop states and robust boundary modes, advancing topological photonics.

Findings

Observation of non-contractible loop states in Kagome lattices

Demonstration of robust boundary modes with self-healing properties

Experimental realization of finite Kagome lattices with desired edges

Abstract

Corbino-geometry has well-known applications in physics, as in the design of graphene heterostructures for detecting fractional quantum Hall states or superconducting waveguides for illustrating circuit quantum electrodynamics. Here, we propose and demonstrate a photonic Kagome lattice in the Corbino-geometry that leads to direct observation of non-contractible loop states protected by real-space topology. Such states represent the "missing" flat-band eigenmodes, manifested as one-dimensional loops winding around a torus, or lines infinitely extending to the entire flat-band lattice. In finite (truncated) Kagome lattices, however, line states cannot preserve as they are no longer the eigenmodes, in sharp contrast to the case of Lieb lattices. Using a continuous-wave laser writing technique, we experimentally establish finite Kagome lattices with desired cutting edges, as well as in the Corbino-geometry to eliminate edge effects. We thereby observe, for the first time to our knowledge, the robust boundary modes exhibiting self-healing properties, and the localized modes along toroidal direction as a direct manifestation of the non-contractible loop states.