# Photonic Anomalous Quantum Hall Effect

## TL;DR

This paper demonstrates a photonic analogue of the anomalous quantum Hall effect using a 2D array of coupled ring resonators, revealing topologically protected edge states and phase transitions relevant for advanced photonic devices.

## Contribution

It introduces a novel photonic system that mimics the anomalous quantum Hall insulator, including topological phase control and pseudospin-dependent edge states.

## Key findings

- Realization of topologically robust edge states in photonic resonator arrays
- Observation of a topological phase transition via frequency detuning
- Pseudospin-dependent propagation of edge states

## Abstract

We experimentally realize a photonic analogue of the anomalous quantum Hall insulator using a two-dimensional (2D) array of coupled ring resonators. Similar to the Haldane model, our 2D array is translation invariant, has zero net gauge flux threading the lattice, and exploits next-nearest neighbor couplings to achieve a topologically non-trivial bandgap. Using direct imaging and on-chip transmission measurements, we show that the bandgap hosts topologically robust edge states. We demonstrate a topological phase transition to a conventional insulator by frequency detuning the ring resonators and thereby breaking the inversion symmetry of the lattice. Furthermore, the clockwise or the counter-clockwise circulation of photons in the ring resonators constitutes a pseudospin degree of freedom. We show that the two pseudospins acquire opposite hopping phases and their respective edge states propagate in opposite directions. These results are promising for the development of robust reconfigurable integrated nanophotonic devices for applications in classical and quantum information processing.