The Nobel Prize for Physics 2025 goes to three physicists, which for the first time proved that quantum tunnels are also possible on a macroscopic scale. John Clarke, Michel Divvoret and John Martinis demonstrated in their experiment that coupled particles of a superconductor circuit can tunnel a barrier-and that this circuit reacts quarreled. This knowledge laid the basis for technologies such as quantum computers and quantum sensors.
In quantum physics, other laws apply than in our macro world. While walls in the world visible to us are impassable for a ball or our body, this is different in the quantum world: atoms and other microscopic particles can usually penetrate such impermeable walls by tuning the energetic or physical barriers. This becomes possible because the whereabouts and the behavior of quantum particles are determined by probabilities. Because its position is not precisely determined, there is a certain, albeit low probability that the particle is beyond the barrier. But is this quantum tunnels possible up to any size?
A superconductor circuit as a test case
This year’s Nobel Prize winners have proven for the first time that this quantum-physical effect is also possible on a macroscopic scale. This was achieved in experiments that John Clarke, Michel Divvoret and John Martinis conceived and carried out at the University of California in Berkeley in 1984 and 1985. The core element of the experiments was a so-called Josephson contact: an arrangement from two superconductors, which are separated from an electrical insulation by a thin barrier. The special thing about supral ladders is their ability to lead electricity without resistance: electrons in such materials combine to form so-called cooper pairs. In these they have the same quantum state and can therefore move as a unit and without resistance. For their experiment, the physicists now led weak electricity to this Josephson contact and measured the tension.
Because both superconductors are separated from the barrier, no electricity should flow, the voltage should be at zero volt. But that was not the case: despite the barrier, the measuring instruments showed a low but clearly existing tension. In this way, these experiments for the first time showed that a superconductive circuit that is “large enough to grab it with his own hands” can show a quantum tunnels on a macroscopic scale. The invited particles flowing by the superconductor were like a unit that overcame the insulator barrier and filled out the entire circuit. Clarke, Divvoret and Martinis also showed that the system behaves as the quantum mechanics predicted: it is quantized and only absorbs certain amounts of energy.
Basis for quantum computers and co
“Once again we celebrate that the centuries -old quantum mechanics always offer new surprises,” says Olle Eriksson, chairman of the Nobel Committee for Physics. The work of the three award winners paved the way to further research quantum -physical phenomena in macroscopic circuits – and thus in the technology, which forms the basis of all digital technology. At the same time, the findings of Clarke, Divvoret and Martinis laid the basis for new technologies such as quantum computers and quantum sensors.
Source: The Royal Swedish Academy of Sciences