Quantum noise in open quantum systems – a real-world story

Quantum systems never live in isolation but are inevitably in contact with fluctuating reservoirs. While this sounds almost trivial, it turns out that even after more than half a century of intensive research, the issue of quantum noise remains a formidable task. In fact, while it appears to be one of the major bottlenecks to realize quantum structures of ever growing complexity and to exploit them in real-world applications, it also opens ways to new resources. In this colloquium I will discuss subtleties and challenges, also in the context of current experimental developments. Particular reference is made to some of our recent contributions to fields such as superconducting circuits, quantum heat engines, and vacancy centers in diamond.