Changes to the aggregate state triggered by quantum effects à in physically correct terms, quantum phase transitions à play a role in many astonishing phenomena in solids, such as high-temperature superconductivity. Researchers from Switzerland, Great Britain, France and China have now specifically altered the magnetic structure of the material TlCuCl3 by exposing it to external pressure and varying this pressure. With the aid of neutrons, they were able to observe what happens during a quantum phase transition, where the magnetic structure melts quantum-physically.