What will the computers of tomorrow look like? Chances are good that spintronics will play a decisive role in the next generation of computers. In spintronics, the intrinsic angular momentum of an electron (the spin) is used to store, process and transmit data. This technology is already in use today, for example in hard drives. However, the scope of what is possible extends much further: More recent approaches aim at using not just individual spins, but entire spin waves made up of partly hundreds of trillions of spins. Such collective spin excitations are known as magnons. They could enable extremely energy-efficient data transmission—even in the terahertz range.