Topological effects in optically anisotropic microcavities

该项目的目的是对拓扑感兴趣微腔（MC）的实验实现和理论理解，以及光子和激子极化子的保护光子态和定向输运的证明。本文对这些示例系统的理论研究有望为描述低对称性系统中的光学模式及其偏振形成一个普遍的新概念奠定基础。此外，拓扑光子系统在基础科学和应用方面都非常有趣，可以预期为实现片上光学数据传输和处理设备提供一个里程碑。激子-极化子在室温及以上温度下建立玻色-爱因斯坦凝聚体的能力进一步显示了这种拓扑系统在量子计算中的应用潜力。作为一个一般的新概念，我们将利用特殊模式特性在光学双轴系统中，其中对称性破缺是由谐振腔结构和相关材料的光学各向异性共同引起的。由光学各向异性、光学线性、互反和非手性空腔材料组成的拓扑非平凡MC将被实验生产、研究和理论理解。用腔光子和激子极化子的性质（复模色散、极化或伪自旋）来证明其非平凡性。利用横向结构，可以解除狄拉克类点的简并性，以诱导拓扑保护边缘模式，并使光子或激子极化子的输运成为可能。在这方面，偏振态或更确切地说，粒子的伪自旋有望受到拓扑保护，从而可以用于实验证明。提出的概念不需要外场、复杂的元材料或本身的拓扑非平凡电子系统，因此具有很好的实际应用前景。基于我们的初步研究，广泛研究和众所周知的光学单轴半导体ZnO和GaN都非常适合作为各自的空腔材料。因此，它们的光轴的方向不能平行于MC的约束方向。首先，我们将实现和研究裸光子MC，用于所用材料的透明光谱范围。一旦成功，我们将把我们的研究扩展到强激子-光子耦合（激子-极化）的体制。

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).