Topological effects in optically anisotropic microcavities

• Applicants: Professor Dr. Ulf Peschel; Privatdozent Dr. Rüdiger Schmidt-Grund
• Subject Area: Experimental Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 329504356

Aim of the project is the experimental realisation and theoretical understanding of topological interesting microcavities (MC), as well as the proof of protected photonic states and directed transport of photons and exciton-polaritons. The theoretical investigations of these exemplary systems here proposed are expected to form a basis for a generally new concept for the description of optical modes and their polarization in systems of low symmetry. Further, topological photonic systems are highly interesting for fundamental science as well as, regarding applications, can be expected to provide a milestone towards the realization of devices for on-chip optical data transport and processing. The capability of exciton-polaritons to build up a Bose-Einstein condensate at room temperature and above show further the potential of such topologic systems for application in quantum computing.As a general new concept, we will utilize special mode properties in optically biaxial systems, in which symmetry breaking is induced by the combination of the resonator structure and the optical anisotropy of the involved materials.Topologically non-trivial MC made out of optically anisotropic, otherwise optically linear, reciprocal and non-chiral cavity materials shall be experimentally produced, investigated and theoretically understood. The non-triviality shall be proven by means of properties (complex mode dispersion, polarization or rather pseudo-spin) of the cavity photons and exciton-polaritons. Using lateral structuring, the degeneracy of Dirac-like points shall be lifted for inducing of topological protected edge-modes and to enable corresponding transport of photons or exciton-polaritons. In this regard, the polarization state or rather the pseudo-spin of the particles is expected to be topological protected and thus can be used for experimental proof. The proposed concept does not need external fields, complicated meta-materials or per se topological non-trivial electronic systems and thus is very promising for practical applications.As based on our preliminary studies, the widely investigated and well known optically uniaxial semiconductors ZnO and GaN are very suitable as respective cavity materials. The orientation of their optical axis thereby must not be aligned parallel to the direction of the confinement of the MC. First, we will realise and investigate bare photonic MC, for the transparency spectral range of the used materials. At success, we will extend our investigations to the regime of the strong exciton-photon coupling (exciton-polaritons).

• DFG Programme: Research Grants