Real-space detection and manipulation of topological edge modes with ultracold atoms

The bulk-boundary correspondence, a fundamental principle relating the topological invariants of the bulk to the presence of edge states, is modified in periodically driven systems. Conventional bulk topological invariants are insufficient to predict the existence of topological edge modes in such systems. Although ultracold atoms provide excellent settings for clean realizations of Floquet protocols, the observation of real-space edge modes has so far remained elusive. Here we demonstrate an experimental protocol for realizing chiral edge modes in optical lattices through the periodic modulation of the tunnelling rate between neighbouring sites. In particular, we show how to efficiently prepare particles in edge modes in three distinct Floquet topological regimes in a periodically driven honeycomb lattice. Controlling the height and amplitude of the potential step, we characterize the emergence of edge modes and the dependence of their group velocity on the sharpness of the potential step. Our direct observation of topological edge modes provides a tool to study topological phases of matter in the presence of disorder and interactions, where conventional bulk observables are not applicable. The observation of edge modes in topological systems is challenging because precise control over the sample and occupied states is required. An experiment with atoms in a driven lattice now shows how edge modes with programmable potentials can be realized.