"Researchers have strived to obtain control of a variety of different quantum systems, each characterized by their own distinct advantages: quantum optical systems offer excellent isolation from the environment while solid state systems allow for integrated micro-fabricated devices. At the same time nuclear spins in molecules can remain decoupled from the environment even under rather harsh conditions, and this is the basis of NMR experiments. Given these distinct advantages it is very fruitful to investigate hybrid devices merging the advantages of each of the systems. To do this it is essential to develop quantum interfaces to connect the different systems. By their very nature such quantum interfaces exchange information with their environment and are therefore open quantum systems.In this project I wish to establish a strong theoretical quantum optics group which can guide and inspire the experiments towards breaking new grounds for open quantum systems and making quantum interfaces between distinct physical systems. The objective is to develop concrete proposals for how to experimentally control and exploit the interaction of quantum systems with their surroundings and for how this can be used for quantum interfaces.The work in this project is particularly relevant for applications in quantum information processing, where the current challenge is to take the field from proof-of-principle demonstrations to truly scalable devices. Such challenge demands new interdisciplinary theoretical ideas for hybrid devices. This proposal addresses several key challenges for quantum information processing: scalable multimode quantum repeaters based on hybrid approaches, entanglement enabled quantum metrology, photonic engineering based on surface plasmons, dissipative preparation of entangled states, and phonon engineering for quantum dots. In addition applications towards nuclear spin cooling to improve NMR experiments as well as ultra cold atoms will be explored."