Nobel Prize awarded for tunnelling in superconducting circuits

The 2025 Nobel Prize in Physics has been awarded to John Clarke, Michel Devoret and John Martinis for their experiments that brought quantum mechanical effects into macroscopic systems.

The Royal Swedish Academy of Sciences cited their ‘discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit’.

In classic quantum mechanics, particles can sometimes cross through energy barriers via a process known as tunnelling, behaviour that typically occurs at atomic or subatomic scales.

The laureates’ work showed that such quantum phenomena can appear in larger electrical circuits using superconductors and Josephson junctions, systems that were thought to be firmly in the domain of classical physics.

Their experiments (conducted in the mid-1980s) involved circuits made of superconducting materials separated by a thin insulating barrier. By finely tuning currents and electromagnetic stimuli, they were able to force a system to switch between zero-voltage and finite voltage states, essentially demonstrating that the circuit could ‘tunnel’ from one state to another.

In addition, they demonstrated energy quantisation in these systems, that the circuits absorb and emit energy in discrete packets, consistent with quantum theory.

This work is widely viewed as a foundational bridge between theoretical quantum mechanics and practical quantum technology. Superconducting circuits (such as qubits in quantum computers) rely on precisely these kinds of effects, and the laureates’ results helped validate the notion that quantum engineering is possible in engineered devices.

As the Nobel announcement puts it, their experiments ‘revealed quantum physics in action’ in a device small enough to hold in hand.

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