The Nobel Prize in Physics for 2025 has been awarded to three researchers: John Clarke from the University of California, Michel H. Devoret from Yale University and the University of California, and John M. Martinis from the University of California. In its reasoning, the Nobel Committee stated that the award recognizes “the discovery of a macroscopic quantum tunneling phenomenon and the quantization of energy in an electrical circuit.” These effects were observed by John Clarke, Michel H. Devoret, and John M. Martinis in experiments conducted in the 1980s.
Quantum tunneling is one of the hallmark effects predicted by quantum physics. It consists in a particle passing through a barrier that, in classical terms, is too high in energy to be crossed. Calculating the transmission coefficient through, for example, a one-dimensional rectangular potential barrier is a standard task in modern physics courses.
The significance of the result achieved by this year’s Nobel laureates lies in the observation of tunneling not of a single particle but of billions of them. This occurs in the so-called Josephson junction, which consists of two superconductors separated by an insulator. In a superconductor, free electrons pair up and move without resistance, allowing a current to flow without an applied voltage. Moreover, the electron pairs on both sides of the junction are described by a single common wave function—that is, they exist in a shared quantum state involving a vast number of particles. It is possible to induce a transition between two different states of this quantum system, and such a transition is an instance of tunneling through the insulator.
In a second experiment, the scientists irradiated the Josephson junction with microwaves and observed that it absorbed the radiation not continuously but in discrete portions—quanta.
The practical significance of these observed effects is currently moderate, but it is expected that they may be used in quantum computers to implement qubits.
An interesting fact is that John Clarke was for many years associated with the University of Cambridge, and he is already the 126th Nobel laureate to come from there.
