Generation of complex multi-photon states in miniaturized semiconductor based quantum devices

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The overarching goal of the project is the generation of multi-photon states via semiconductor quantum devices. Such multi-photon states are of highest interest in the field of photonic quantum technology. For instance, so called N-photon NOON-states allow for ultra-precise phase measurements beyond classical limits. While single photons with excellent quantum nature can be generated with emission rates via highly optimized quantum-light sources, the creation of multi-photon states is still at its infancy. Because of the manifold application scenarios and very interesting scientific questions there has been strongly increasing interest in this very attractive and widely unexplored area of quantum nanophotonics, and corresponding works show the attractiveness and feasibility of related approaches. However, it has become clear that further progress in terms of more advanced concepts and applications in quantum technology require a much deeper understanding of the underlying processes and a better control of the nanophotonics sructures. Against this background the present project aims at the controlled generation and study of multiphoton-states by integration single semiconductor quantum dots deterministically into micropillar cavities and microlenses. This nanophotonics integration enhances both the light-matter interaction and the photon-extraction efficiency of the structures. The quantum dot devices will be combined with piezo-actuators to control their spectral properties in a convenient and reproducible way via variations of the applied voltage. These technological activities together with sophisticated quantum spectroscopy methods, such as two-photon resonant excitation, will be the basis for the extensive experimental studies of the proposed project. The scientific questions focus on the generation of multi-photon states via the biexciton-exciton cascade of semiconductor quantum dots. The rich physics of this cascade and the resonant drive of its transitions via two-photon excitation will be used to generate for instance two- and N-photon bundles by means of “leapfrog”-processes between dressed states of the cascade. A further key activity will address the creation of polarization entangled photon-pairs and N=4 NOON states, again by using the resonantly excited biexciton-exciton cascade. Beyond that we plan to perform Franson-interferometry by using biexciton-exciton photon-pairs to demonstrate the violation of Bell’s inequality. Each task will benefit in all aspects from an intensive and close interaction between the three partners. The planned cooperation is based on established and longstanding joint experience. It uses and ideally complements the complementary expertise of the involved groups in semiconductor technology and advanced semiconductor spectroscopy to reach the challenging goals of the project.