Quantum Optics Seminar by Ewold Verhagen

Direct observation of topologically protected edge states in silicon photonic crystals: Propagation, dispersion, and chirality

The concept of topological protection in photonics offers new prospects for guiding and manipulating classical and quantum information. The mechanism of spin-orbit coupling promises the emergence of edge states that are helical; offering unidirectional propagation that is topologically protected against back-scattering. We demonstrate a photonic analogue of an electronic topological insulator by forming an interface between two silicon photonic crystals with different band topologies. These states can be optically excited and detected through far-field radiation. Importantly, we find that this radiation carries a signature of the underlying photonic spin-orbit coupling: The created helical edge states have unique circular polarization linked to the states' pseudospin. We thus use the far-field radiation channel to selectively excite different edge states with polarized light, and also to map their dispersion and directly visualize their propagation.