Starting with the original proposal by Datta and Das1 for a spin-based field-effect transistor, the field of spintronics2 has explored how the spin degrees of freedom can be used for information transfer. More than two decades later, this research has reached the quantum regime3. One motivation for this is the desire for miniaturization which led to the realization of single-electron transistors4, or more generally single-dopant devices5. A second motivation is the potential applications in quantum information and computation. Two guiding proposals in the field involve implementation of quantum gate operations in quantum dots6 and in doped silicon7. Shortly thereafter, molecular magnets have also been proposed8. It was subsequently shown that universal quantum computation can be realized with Heisenberg exchange interaction, known from quantum magnetism, alone910.