The forces between particles, atoms, molecules, or even macroscopic objects like magnets are determined by the interactions of nature. For example, two closely lying bar magnets realign themselves under the influence of magnetic forces. A team led by Prof. Dr. Matthias Weidemüller and Dr. Gerhard Zürn at the Center for Quantum Dynamics of Heidelberg University has now succeeded in its aim to change not only the strength but also the nature of the interaction between microscopic quantum magnets, known as spins. Instead of falling into a state of complete disorder, the especially prepared magnets can maintain their original orientation for a long period. With these findings, the Heidelberg physicists have successfully demonstrated a programmable control of spin interactions in isolated quantum systems.