University of Cambridge alumnus Professor John Clarke has been awarded the 2025 Nobel Prize in Physics, jointly with Michel H. Devoret and John M. Martinis, for their work revealing quantum physics in action.
Clarke, who is Professor Emeritus of the Graduate School at the University of California at Berkeley, completed both his undergraduate and PhD studies at Cambridge. He was born in Cambridge and attended the Perse School on an academic scholarship before coming to Christ's College as an undergraduate to read Natural Sciences.
Clarke moved to Darwin College for his PhD, which he completed in 1968 at the Cavendish Laboratory. His research is based on the theory, design and applications of superconducting quantum interference devices (SQUIDs), which are ultrasensitive detectors of magnetic flux.
"John Clarke, together with Michel Devoret and John Martinis, pushed the door open for today's quantum technologies based on superconducting qubits, putting fundamental quantum phenomena at work in real devices," said Professor Mete Atature, Head of the Cavendish Laboratory. "Brian Josephson - another Cavendish Nobel Laureate - was first to propose the concept of a new quantum phase arising from tunnelling between two superconductors. John Clarke's PhD work in the Cavendish Laboratory demonstrated the operational principle of what we call a superconductor-normal-superconductor (SNS) Josephson Junction - essentially the heart of all superconducting qubits today. Devoret and Martinis spearheaded the translation of this fundamental quantum physics concept into what superconducting quantum computing is today. I'm of course thrilled with today's well-deserved announcement."
A major question in physics is the maximum size of a system that can demonstrate quantum mechanical effects. Clarke, Devoret and Martinis conducted experiments with an electrical circuit in which they demonstrated both quantum mechanical tunnelling and quantised energy levels in a system big enough to be held in the hand.
Quantum mechanics allows a particle to move straight through a barrier, using a process called tunnelling. As soon as large numbers of particles are involved, quantum mechanical effects usually become insignificant. The laureates' experiments demonstrated that quantum mechanical properties can be made concrete on a macroscopic scale.
In 1984 and 1985, Clarke, Devoret and Martinis conducted a series of experiments with an electronic circuit built of superconductors, components that can conduct a current with no electrical resistance. In the circuit, the superconducting components were separated by a thin layer of non-conductive material, a setup known as a Josephson junction. By refining and measuring all the various properties of their circuit, they were able to control and explore the phenomena that arose when they passed a current through it. Together, the charged particles moving through the superconductor comprised a system that behaved as if they were a single particle that filled the entire circuit.
This macroscopic particle-like system is initially in a state in which current flows without any voltage. The system is trapped in this state, as if behind a barrier that it cannot cross. In the experiment the system shows its quantum character by managing to escape the zero-voltage state through tunnelling. The system's changed state is detected through the appearance of a voltage.
The laureates could also demonstrate that the system behaves in the manner predicted by quantum mechanics - it is quantised, meaning that it only absorbs or emits specific amounts of energy.
Professor Deborah Prentice, Vice-Chancellor of the University of Cambridge, said: "Congratulations to Cambridge alumnus Professor Clarke on being jointly awarded this year's Nobel Prize in Physics for his research into quantum mechanical tunnelling. Not only did he grow up in this incredible city, but he studied from his undergraduate degree through to his PhD here.
"Professor Clarke joins 125 other noteworthy Cambridge alumni and researchers who have been awarded Nobel Prizes, highlighting our University's remarkable impact within the research and education sectors."
Clarke has continued his active affiliation with Cambridge over the years, returning several times, including 1972 when he was elected to a Fellowship at Christ's, 1989 when he was a Visiting Fellow at Clare Hall, and 1998 when he was elected a By-Fellow of Churchill College. He was awarded the ScD from the University in 2003, and was elected an Honorary Fellow of Darwin College in 2023.
John Clarke is the 126th affiliate of the University of Cambridge to be awarded the Nobel Prize.
