# Topological properties of a dense atomic lattice gas

## TL;DR

This paper explores topological phases in a dense 2D atomic lattice gas, revealing how long-range interactions and dissipation influence edge transport and can break traditional bulk-boundary relations.

## Contribution

It demonstrates the existence of topological phases in a dense atomic lattice with long-range interactions, highlighting robustness of edge transport despite dissipation and defects.

## Key findings

- Long-range interactions cause one-sided divergences in energy spectra.
- Topological edge transport remains robust despite dissipation.
- Standard bulk-boundary relation can be broken by long-range interactions.

## Abstract

We investigate the existence of topological phases in a dense two-dimensional atomic lattice gas. The coupling of the atoms to the radiation field gives rise to dissipation and a non-trivial coherent long-range exchange interaction whose form goes beyond a simple power-law. The far-field terms of the potential -- which are particularly relevant for atomic separations comparable to the atomic transition wavelength -- can give rise to energy spectra with one-sided divergences in the Brillouin zone. The long-ranged character of the interactions has another important consequence: it can break of the standard bulk-boundary relation in topological insulators. We show that topological properties such as the transport of an excitation along the edge of the lattice are robust with respect to the presence of lattice defects and dissipation. The latter is of particular relevance as dissipation and coherent interactions are inevitably connected in our setting.