Quantum optics: fundamental tests and quantum technology

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Quantum optics studies the interaction of light and matter at the quantum level. This area, which has been at the core of the development of quantum physics from the very beginning, continues to be exceptionally well suited for fundamental tests of quantum physics, but also for the development of new technologies based on basic quantum phenomena. One such phenomenon is quantum entanglement, which allows quantum particles to be connected even if they are far apart in space. In my theoretical research I develop proposals for experiments that will advance both the fundamental and the applied side of our field.***The first main question that motivates my research is whether it will be possible to extend entanglement to global distances. This is interesting both from a fundamental point of view and for information technology, because it will provide secure global communication via quantum cryptography. Ultimately it will also allow the construction of a quantum internet, linking future quantum computers on a global scale. Quantum computers promise to solve problems that are intractable with conventional computers. I approach this question by designing architectures for global quantum communication  and by making proposals for the implementation of the various components that these architectures require. ***The second main question is whether quantum physics, which has passed many experimental tests at the microscopic scale, also applies to macroscopic systems, or whether the theory has to be modified at some level of system size or complexity. Such a modification could for example be due to the unification of quantum physics and gravitation, which is one of the big unsolved problems in modern physics. I approach this question by developing proposals for experiments that should allow the creation and observation of quantum effects in increasingly complex and macroscopic systems, which then also allows one to test various modifications of quantum physics that have been proposed. ***The work described in this application will make significant steps towards answering both of these questions. On the one hand, the investigations proposed here will make the path towards global entanglement much clearer. The area of long-distance quantum communication also has the potential for commercial applications, and theoretical work on the physical implementation is essential for taking our field to that point. On the other hand, the present work will help to push the boundaries of quantum physics, and to lay the foundation for discovering what lies beyond.**