An integrated semiconductor platform for the implementation and study of higher-order exceptional points

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The transfer of basic concepts of open wave or quantum systems to highly integrated solid-state devices is of paramount importance both for a deeper understanding of the underlying physics and for the innovation of new technologies and devices. In recent years, non-Hermitian systems came into focus including those exhibiting parity-time symmetry. The main reason for the rising interest are so-called exceptional points (EPs) in parameter space, which are exotic degeneracies at which two or more energy eigenvalues and the corresponding eigenstates coalesce. Among a range of interesting fundamental aspects, these degeneracies have great potential for ultrasensitive sensing devices. Potentially, even more so when going from second-order EPs to EPs of nth order, where n energy eigenvalues and -states coalesce. This interdisciplinary research project is positioned at the border between experimental solid-state optics and theoretical non-Hermitian photonics. The Magdeburg group will lay the groundwork and establish the theoretical backbone using coupled-mode theory and numerical simulations to obtain parameter sets suitable for (higher-order) EPs and to evaluate the sensing potential of simulated devices. The Würzburg group will use its expertise in semiconductor epitaxy and device fabrication to realize tailored EP-devices based on scaleable group-III-V materials. The device fabrication and optimization will be closely tied to the numerical simulations and performed efficiently in an iterative way. The goal of this project is to develop a robust and versatile integrated semiconductor platform that allows to combine the concept of EPs with the mechanism for the creation of so-called exceptional surfaces in parameter space and the resulting robust EPs. Using large scale device characterization techniques and laser scanning techniques we will map out the experimental parameter space and realize second- and third-order EPs in ring laser devices coupled to suitable bus waveguides. We will use sophisticated spectroscopic techniques to characterize the fabricated device properties, demonstrating the desired nth-root scaling of the systems response to perturbations. Using an artificial scatterer – both lithographically defined and mobile – we will explore the sensing capabilities of these scaleable devices. In a later stage of the project we will turn our attention to mapping the energy surfaces in the vicinity of the EPs. In doing so, we will get valuable insight into the yet not well understood topology around higher-order EPs, which will connect our research to the exciting new field of topological photonics.