Topological states of light and matter: Open, yet stable
Topological materials isolated from their surroundings exhibit remarkable stability against disorder, e.g., from structural imperfections. Typically, coupling such systems to their environments reduces or even destroys thisstability. Now a collaboration between experimental and theoretical groups from the University of Bonn and RPTU Kaiserslautern-Landau within the SFB TR 185 “Open System Control of Atomic and Photonic Matter” (OSCAR) has successfully realized a new approach to reverse this paradigm. By carefully tailoring losses in an open hybrid light-matter waveguide system, the researchers experimentally observed the controlledemergence and breakdown of topological edge states.
In the experimental project, which was initiated and led by Dr. Julian Schmitt from the University of Bonn, the team demonstrated the dissipation-induced emergence of a topological band structure in a non-Hermitian one-dimensional lattice system, realized by arrays of plasmonic waveguides with tailored loss. The PMMA-on-gold samples with spatially distributed absorption losses induced by thin Chromium stripes were fabricated and optically investigated in the group of Stefan Linden at Bonn. From their measurements of light propagation following an excitation with laser light, the team obtained direct evidence for a topological edge state that resides in the center of the band gap. By tuning dissipation and hopping in the waveguide array, the formation and breakdown of an interface state between topologically distinct regions were found, in excellent agreement with theory predictions carried out by Michael Fleischhauer at Kaiserslautern. In the lossy waveguides light only travels a finite distance. The researchers showed that making the system topological helped increasing this distance in the edge waveguides. These findings indicate an advantage of topological states in open systems relevant for potential future technologies in quantum optics and photonics.