Observation of chiral edge transport in a rapidly-rotating quantum gas

TL;DR

This paper demonstrates the creation and control of chiral edge states in a rapidly-rotating bosonic superfluid, revealing how boundary sharpness influences edge mode behavior and energy gaps.

Contribution

It introduces a method to observe and manipulate chiral edge states in a quantum gas, bridging soft and hard boundary regimes and analyzing their spectral properties.

Findings

Edge states can be tuned by boundary sharpness.

Energy gap evolution from Landau levels to hard wall regimes.

Observation of chiral edge transport in a quantum gas.

Abstract

The frictionless, directional propagation of particles at the boundary of topological materials is one of the most striking phenomena in transport. These chiral edge modes lie at the heart of the integer and fractional quantum Hall effects, and their extraordinary robustness against noise and disorder reflects the quantization of Hall conductivity in these systems. Despite their central importance, controllable injection of edge modes, and direct imaging of their propagation, structure, and dynamics, is challenging. Here, we demonstrate the distillation of individual chiral edge states in a rapidly-rotating bosonic superfluid confined by an optical boundary. Tuning the wall sharpness, we reveal the smooth crossover between soft wall behaviour in which the propagation speed is proportional to wall steepness, and the hard wall regime exhibiting chiral free particles. From the skipping motion of atoms along the boundary, we spectroscopically infer the energy gap between the ground and first excited edge bands, and reveal its evolution from the bulk Landau level splitting for a soft boundary, to the hard wall limit.