Significance of the 2025 Nobel Prize in Physics An interview with Christoph Bruder and Andrea Hofmann on quantum mechanics in ma- croscopic systems On 10 December, 2025, the Nobel Prize in Physics was awarded to Professor John Clarke, Professor Michel H. Devoret and Professor John M. Martinis for their discovery of macroscopic quantum mechanical tunneling and energy quantization in an electric circuit. Their experiments show that quantum effects play a role not only in the nano and micro- world but also in larger, macroscopic systems. Professor Christoph Bruder and Professor Andrea Hofmann from the Department of Physics discuss this groundbreaking research in an interview. SNI INSight: What exactly have the three researchers been awarded the Nobel Prize for? Christoph Bruder: Back in the 1980s, Clarke, Devoret and Martinis carried out experiments proving that a circuit con- sisting of superconducting components shows quantum mechanical effects — de- spite being a large system involving many particles. At the time when these experiments were performed, scientists had already known about the phenomenon of quan- tum tunneling for some time. They had observed that individual quantum parti- cles can pass through an insulating bar- rier — in a manner that completely con- tradicts our experience of the mac- roworld. In other words, if we throw a ball against a wall, it bounces back and doesn’t suddenly appear on the other side. It remained unclear, however, whether this phenomenon could also ap- pear in the macroscopic world — and up to which point quantum effects come into play. Through their experiments, the three researchers who have now been awarded the Nobel Prize showed that this tunnel- ing effect could also be observed in a mac- roscopic system. SNI INSight: How did they do it? Christoph Bruder: Clarke, Devoret and Martinis used a circuit made up of two superconductors separated by a thin, in- sulating barrier to create “Josephson junctions.” The particles then tunneled through the insulating barrier. This was only possible, however, because the re- searchers cooled the system down to a very low temperature and, above all, be- cause they shielded it very efficiently. In- tended to prevent the effects from being masked by outside interference, this pre- sented a significant technical challenge. In their experiments, the researchers were able to show that all the charged particles in the superconductor exhibited uniform behavior. To put it simply, the system has two states: one in which cur- rent flows without a voltage, and another in which a voltage appears when a current flows. The experiments showed that all particles tunneled collectively between these two states despite the barrier. The researchers also demonstrated that the system is quantized, which means that it can only absorb and emit specific amounts of energy. SNI INSight: What’s so special about that? Christoph Bruder: In larger, macroscopic systems, quantum mechanical effects are often destroyed due to heat or interac- tions with the environment — and it is 7 SNI INSight December 2025