# Topologically Protected Quantum Coherence in a Superatom

## TL;DR

This paper theoretically demonstrates that a topological atom array acts as a superatom with edge states exhibiting topology-protected quantum coherence, useful for quantum memory and quantum optics.

## Contribution

It introduces a topological superatom model with protected edge states and analyzes their quantum coherence and phase transition behaviors in a cavity system.

## Key findings

- Edge states exhibit topology-protected quantum coherence.
- Identification of a superradiance-subradiance transition.
- Quantum coherence of edge states is robust to noise.

## Abstract

Exploring the properties and applications of topological quantum states is essential to better understand topological matter. Here, we theoretically study a quasi-one-dimensional topological atom array. In the low-energy regime, the atom array is equivalent to a topological superatom. Driving the superatom in a cavity, we study the interaction between light and topological quantum states. We find that the edge states exhibit topology-protected quantum coherence, which can be characterized from the photon transmission. This quantum coherence helps us to find a superradiance-subradiance transition, and we also study its finite-size scaling behavior. The superradiance-subradiance transition also exists in symmetry-breaking systems. More importantly, it is shown that the quantum coherence of the subradiant edge state is robust to random noises, allowing the superatom to work as a topologically protected quantum memory. We suggest a relevant experiment with three-dimensional circuit QED. Our study may have applications in quantum computation and quantum optics based on topological edge states.