Topological spin texture of chiral edge states in photonic two-dimensional quantum walks

TL;DR

This paper experimentally demonstrates topological spin textures in chiral edge states of a 2D photonic quantum walk, revealing nontrivial winding linked to bulk topological properties, with implications for spintronics.

Contribution

It provides the first experimental observation of topological spin textures in boundary states of a 2D Floquet topological phase using photonic quantum walks.

Findings

Chiral edge states exhibit nontrivial spin winding on the Bloch sphere.

The spin texture is linked to the bulk Dirac Hamiltonian.

Edge spin textures could enable new spintronic devices.

Abstract

Topological insulators host topology-linked boundary states, whose spin and charge degrees of freedom could be exploited to design topological devices with enhanced functionality. We experimentally observe that dissipationless chiral edge states in a spin-orbit coupled anomalous Floquet topological phase exhibit topological spin texture on boundaries, realized via a two-dimensional quantum walk. Our experiment shows that, for a walker traveling around a closed loop along the boundary in real space, its spin evolves and winds through a great circle on the Bloch sphere, which implies that edge-spin texture has nontrivial winding. This winding is linked to the bulk Dirac Hamiltonian around the energy-gap opening point. Our experiment confirms that two-dimensional anomalous Floquet topological systems exhibit topological spin texture on the boundary, which could inspire novel topology-based spintronic phenomena and devices.