A new concept for a unidirectional waveguide

In the past decade, a new type of material has attracted raising attraction: the so-called topological insulator. This class of materials exhibits a very peculiar property: they behave like insulators in the interior, but contain conducting states at their boundaries. As these states are "topologically" protected (see below), the states are very robust against imperfections, and electric currents can flow almost without any dissipation. This makes these materials extremely interesting for the task of quantum communication and quantum computing, for example.

Now Dr. Tao Shi (at present Chinese Academy of Sciences, Beijing) and Prof. Ignacio Cirac from the Max Planck Institute of Quantum Optics in Garching, together with Prof. Jeff Kimble from the California Institute of Technology (Pasadena, USA), have developed a detailed scheme for an experimental setup to realize a 2-dimensional topological insulator with classical optical networks (Proceedings of the National Academy of Sciences, AOP 10 October 2017). "In this network, photon modes play the role of the electronic states in a solid state layer," explains Dr. Tao Shi. "By preparing chiral photon modes at the boundary, we may be able to build a one-way electromagnetic waveguide, in which light can only propagate in one direction, while the opposite direction is prohibited."