A terahertz laser makes it possible to control a material’s magnetization at a timescale of picoseconds (0.000,000,000,001 seconds). In their experiment, the researchers shone extremely short light pulses from the laser onto a magnetic material, where the magnetic moments – “elementary magnets” – were all aligned in parallel. The light pulse’s magnetic field was able to deflect the magnetic moments from their idle state in such a way that they exactly followed the change of the laser’s magnetic field with only a minor delay.