3 win physics Nobel for discovery of macroscopic quantum mechanical tunnelling

• US-based scientists John Clarke, Michel Devoret and John Martinis won the 2025 Nobel Prize in Physics for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.

• They used a series of experiments to demonstrate that the bizarre properties of the quantum world can be made concrete in a system big enough to be held in the hand. 

• Their superconducting electrical system could tunnel from one state to another, as if it were passing straight through a wall. 

• They also showed that the system absorbed and emitted energy in doses of specific sizes, just as predicted by quantum mechanics.

This year’s winners:

a) John Clarke was born 1942 in Cambridge, UK. He is a professor at University of California, Berkeley, USA.

b) Michel H. Devoret was born in 1953 in Paris, France. He is a professor at Yale University, New Haven, CT and University of California, Santa Barbara, USA.

c) John M. Martinis was born in 1958. He is a professor at University of California, Santa Barbara, USA.

Quantum mechanical tunnelling

• Quantum mechanics describes properties that are significant on a scale that involves single particles. 

• In quantum physics, these phenomena are called microscopic, even when they are much smaller than can be seen using an optical microscope. 

• This contrasts with macroscopic phenom­ena, which consist of a large number of particles. 

• For example, an everyday ball is built up of an astronomical amount of molecules and displays no quantum mechanical effects. We know that the ball will bounce back every time it is thrown at a wall. 

• A single particle, however, will sometimes pass straight through an equivalent barrier in its microscopic world and appear on the other side. 

• This quantum mechanical phenomenon is called tunnelling.

Their experiments revealed quantum physics in action

• The three scientists 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.

• As soon as large numbers of particles are involved, quantum mechanical effects usually become insignificant. 

• Their experiments demonstrated that quantum mechanical properties can be made concrete on a macroscopic scale.

• In 1984 and 1985, the trio 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.

• This component is named after Brian Josephson, who performed quantum mechanical calculations for the junction. The Josephson junction rapidly found areas of application, including in precise measurements of fundamental physical constants and magnetic fields. 

• 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.

• They 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.

• The transistors in computer microchips are one example of the established quantum technology that surrounds us. 

• The findings have provided opportunities for developing the next generation of quantum technology, including quantum cryptography, quantum computers, and quantum sensors.