Bloch Oscillations and Zener Tunneling of Exciton Polariton Condensates in One- and Two-dimensional Lattices

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The transfer of basic concepts of quantum mechanics to highly integrated solid state devices is of highest interest for a deeper understanding and hence the creation of new technologies and devices based on enhanced light-matter interaction. This interdisciplinary research project is positioned at the border between solid state physics and optics and between theoretical and experimental physics. It focuses on the transfer of basic concepts of quantum mechanics to an exciton-polariton system. Exciton-polaritons are quasi-particles arising from the strong coupling of an electromagnetic field (photons) to an excited state of matter (excitons). The project aims on the experimental realization and observation of very fundamental phenomena such as Bloch oscillations and Zener tunneling which are directly associated with the propagation of quantum particles (including photons) in periodic structures being subject to external driving forces. The particular nature of the exciton-polariton system will for the first time allow for a detailed analysis of two-dimensional Bloch oscillations. The inherent nonlinearity of the exciton-polaritons caused by many-body interactions will also allow us getting deeper inside into the fascinating physics of superfluidity. The project comprises both theoretical (University of Jena) and experimental (University of Würzburg) investigations, bringing together two of the leading groups in the field of optical Bloch oscillations and exciton-polariton physics. We will investigate quantum coherence phenomena based on the excitation and propagation of exciton-polariton quasi particles in resonantly excited nanostructured semiconductor cavities. We will first study the propagation of exciton-polaritons in an effective potential corresponding to an array of coupled waveguides being excited under oblique incidence. Fields propagating along the guides will be subject to transverse forces induced by thickness variations of the sample. Resulting Bloch oscillations and Zener tunneling will be mapped to a spatial elongation thus allowing for an observation of their fast dynamics. Later we will turn our attention to the evolution of fields in biased two-dimensional lattices and to the resulting periodic evolution which is now detected via ultrafast spectroscopy. All investigations will be performed for varying intensities thus monitoring the transition from linear to nonlinear dynamics and the onset of super fluidity. The overall aim of our project is to control the fast dynamics of exciton polariton condensates on nanoscale dimensions using structured semiconductors. The proposed research will equally contribute to the field of nonlinear optics and modern solid state physics. The technology platform which will be applied and extended in this project will also have a significant impact on the design of new laser and microcavity structures, thus a broad field of integrated semiconductor quantum photonics.