"Spins in solids are at the heart of fundamental physical phenomena such as magnetism. Today, they are harnessed in a range of technologies such as magnetic resonance imaging and spintronics for recording media. The revolutionary potential of future quantum technologies has fuelled research efforts to gain control of the quantum nature of spins. Thanks to a string of recent breakthroughs, it is now possible to initialize and read out individual spins in a solid, and to manipulate their dynamics using carefully defined control fields. However, all experiments to date have been limited to “open-loop” control on locally interacting few-spin systems, precluding efficient correction of noise and errors and preventing long-distance applications.My HYSCORE project will realize two critical breakthroughs: “closing the loop” by performing quantum feedback and generating quantum entanglement between remote spins. These goals will allow for entering a new era, in which robustly controlled spin registers are connected to form true quantum networks.To achieve these ambitious goals, I will exploit and combine the key strengths of different types of quantum information carriers: the robustness of nuclear spins for storage and core computational tasks, the optical interface of electron spins for initializing and reading the nuclear spin registers, and the mobility and coherence of photons for establishing truly long-distance links. Two promising solid-state platforms will be studied: nitrogen-vacancy defects in diamond and fluorine donors in zinc selenide. If successful, HYSCORE will yield novel methods for closed-loop quantum control, fundamental insights into quantum measurement, robust multi-qubit registers in a solid, and the establishment of elementary long-distance quantum networks."