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Presented by Professor Göran Johansson
Member of the Royal Swedish Academy of Sciences
Member of the Nobel Committee for Physics

Your Majesties, Your Royal Highnesses,
Esteemed Nobel Prize Laureates, Ladies and Gentlemen,

The fundamental and yet counterintuitive laws of quantum physics have inspired human imagination since they were discovered. One hundred years ago, in the summer of 1925, Werner Heisenberg discovered matrix mechanics while escaping pollen and hay fever on the tiny, rocky island of Helgoland in the North Sea. In December that same year, Erwin Schrödinger took a train through nineteen tunnels to reach the small, beautiful mountain village of Arosa in Switzerland, where he first wrote down his wave equation, which governs the motion of quantum mechanical particles, during a Christmas skiing vacation.

Based on Schrödinger’s description, it was immediately clear that if an electron could go skiing, it would somehow simultaneously explore the path both to the left and the right of any tree down the hill. When you and I ski, not choosing a specific route around a tree would lead to a painful disaster. Furthermore, quantum particles can explore the other side of seemingly impenetrable barriers, as if they dig their own tunnels on the fly, while Schrödinger’s train certainly needed real tunnels.

Our human bodies, as well as trains, exclusively consist of quantum particles, so how come we have no personal experiences of such quantum tunnelling? The main reason is that these striking quantum features are extremely sensitive to interaction with the environment. Large composite objects, upon which we build our intuition, interact far too strongly both with us and with the rest of their environment to behave in a quantum manner. Thus, to observe fragile quantum effects in larger systems, they need to be very carefully isolated, even more than what Heisenberg and Schrödinger themselves needed for their initial theoretical discoveries.

This year’s Nobel Prize laureates in physics, John Clarke, Michel Devoret and John Martinis, managed to give billions of electrons, moving in an electric circuit on a silicon chip, enough secluded privacy to collectively exhibit both quantum tunnelling and energy quantisation. This involved cooling them down to only one hundredth of a degree above absolute zero, cooler than in outer space. This freezes out most of the disturbing environment and forces the electrons to form so-called Cooper pairs, thereby losing their identity, all behaving in exactly the same way and becoming superconducting.

In order to control these Cooper pairs with microwaves but still shield them from the abundance of thermal microwaves at room temperature, they invented a new type of filter, damping the signal twenty orders of magnitude before reaching the system. Listening to a rocket launch through a similar sound filter would sound far less than a ticking watch.

The amazing and curiosity-driven discovery that superconducting electrical circuits on a silicon chip, like this, clearly visible to the naked eye and containing billions of electrons can still exhibit the delicate quantum effect of tunnelling as well as absorbing microwaves in small packages, or quanta, just like natural atoms, established superconducting circuits as a platform for exploring quantum physics with engineerable artificial atoms as well as for developing future quantum technology.

Professor John Clarke, Professor Michel Devoret and Professor John Martinis, you have been awarded the 2025 Nobel Prize in Physics “for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.” It is an honour and a privilege to convey to you, on behalf of the Royal Swedish Academy of Sciences, our warmest congratulations.

I now ask you to step forward to receive your Nobel Prizes from the hands of His Majesty the King.

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