The concept of gauge fields plays a significant role in many areas of physics, from particle physics and cosmology to condensed-matter systems, where gauge potentials are a natural consequence of electromagnetic fields acting on charged particles and are of central importance in topological states of matter(1). Here, we report on the experimental realization of a synthetic non-Abelian gauge field for photons(2) in a honeycomb microcavity lattice(3). We show that the effective magnetic field associated with transverse electric-transverse magnetic splitting has the symmetry of the Dresselhaus spin-orbit interaction around Dirac points in the dispersion, and can be regarded as an SU(2) gauge field(4). The symmetry of the field is revealed in the optical spin Hall effect, where, under resonant excitation of the Dirac points, precession of the photon pseudospin around the field direction leads to the formation of two spin domains. Furthermore, we observe that the Dresselhaus-type field changes its sign in the same Dirac valley on switching from s to p bands, in good agreement with the tight-binding modelling. Our work demonstrating a non-Abelian gauge field for light on the microscale paves the way towards manipulation of photons via spin on a chip.

A spin-orbit coupling effect in photonic graphene made of coupled polaritonic microcavities is experimentally realized, revealing the unique fine structure of the eigenstates around the Dirac points, with the formation of a Dresselhaus-like effective magnetic field that can be mapped to a non-Abelian gauge field.

Read full paper: Optical analogue of Dresselhaus spin-orbit interaction in photonic graphene