The Nobel Prize in Chemistry isn’t the only Nobel prize that has been awarded this October. Perhaps one of the most interesting awards has been given to John Clarke, Michel Devoret and John Martinis for their work on quantum tunneling. When they worked on this in the 1980’s, quantum physics was seen as a very abstract and highly theoretical discipline. With their research, the Nobel laureates showed that quantum physics could also be observed in a macroscopic system. Nowadays, quantum physics has many more practical applications, for example it is especially important for electronics: like in the production of semiconductors or transistors.

1. A brief introduction to quantum mechanics
2. Probability and Wave functions
3. Quantum Tunneling
4. The Experiment
5. Theory against the Universe?
6. Setting the tone for quantum computing

The laureates showed that quantum tunneling could occur on a larger scale and wasn’t exclusively theory. But, what is “quantum tunneling” and why is it so important?

A brief introduction to quantum mechanics

John Dalton gave one of the first descriptions of the atom in 1804. He hypothesized that atoms were the smallest quantity that made up everything and couldn’t be divided. Yet only 100 years later, the atom was split. This splitting of the atom would later find application in nuclear physics: in particular in building the first nuclear bomb as part of the Manhattan project. In the early 21st century, researchers at CERN discovered the Higgs Boson, an elementary particle smaller than even a neutron or a proton.

Theories change over time, and so do the applications we can derive from them. One of the most notable advancements in atom theory has been quantum mechanics. It describes electrons not just as negatively charged dots that can move between shells (the Bohr model). Rather, electrons don’t have a set position, they are described as having a probability of being at a certain location at a certain time. If you draw a dot at every position where an electron is expected to be, you’d get a shape called an orbital. Say, at distance r=3 from the nucleus, the electron has a 90% chance of existing, then you’d get a cluster of dots in that place. The opposite would occur if it only has a 10% chance: you’d barely find any dots there.

Probability and Wave Functions

So what dictates the probability of finding an electron in a certain location? Well quantum mechanics describes electrons as waves, just like classical physics describes water or sound waves. So electrons are described by a wave function Ψ, in particular one that satisfies the Schrödinger equation. We can interpret the Schrödinger equation as essentially being a function that allows us to plot the probability of finding an electron against its distance from the nucleus¹. As such, if we analyze one of those diagrams, it looks a bit like this:

As you can see, there is a higher probability of finding electrons at certain distances from the nucleus. So this wave function is kind of just a mathematical way of representing an orbital.

Quantum Tunneling

To get back to laureates who won this year’s Nobel prize, let’s look at the theory behind their experiment. Quantum mechanics describes electrons as wave functions with stochastic qualities. So the result of looking at probabilities always means there is a particular uncertainty associated with every statement. According to classic physics, throwing a ball at a wall will make it bounce back. This stems from the fact that it won’t have enough energy to surpass the wall. Think of throwing a ball at a wall of bricks vs. one of paper. Clearly in one scenario the wall is too weak, allowing the ball’s energy to be enough to overcome it. Though with extremely small particles, quantum physics says that particles with not enough energy could actually still bypass the “wall” instead of bouncing back.

Quantum mechanics calls this wall a potential barrier and, as the name implies, it is only potentially a barrier to particles. If we take the wave function described earlier and place it against a barrier, we can observe that part of the function still exists beyond the barrier. This means that there is a small probability of an electron existing outside the barrier.

This possibility of finding an electron “on the other side” defines quantum tunneling. Although electrons with more energy have different wave functions that might have higher probabilities beyond the barrier This means that scientists can control tunneling by allowing quantum particles to have specific energies. For example, scanning tunneling microscopes (STMs) are a practical application of quantum tunneling. They can be used to make images at an atomic level by leveraging quantum tunneling.

The Experiment

In a series of papers, Clarke, Devoret and Martinis built an electric circuit where they could observe particles’ qualities. This circuit consisted of two superconductors with a non-conducting material placed between them, known as a Josephson Junction. A conductor is any material that allows electrons to pass through it, for example a metal. Consequently a superconductor is a material that acts as a conductor, but poses no resistance to the moving electrons. Resistance typically occurs due to the innate structure of a material that makes it harder to move through or collisions between electrons due to high temperatures. As a result, electrons in superconductors move in pairs, known as Cooper pairs, when cooled to extremely low temperatures.

Subsequently a non-conductive material, an insulator, is put between these two superconductors. Now, due to quantum tunneling, some of the electrons in the superconductors can tunnel through the insulator. This is known as the Josephson effect. Therefore, the whole setup with the two superconductors and the insulator is known as a Josephson Junction.

Theory against the Universe?

The Nobel laureates used this junction to investigate the properties of their current. Because the electrons were flowing through a superconductor as joint Cooper pairs, they behaved like a single quantum entity. In short, they could be described with a single wave function.

The fact that the current in this experiment could be described with a single wave function proved to be extremely useful.

Normally a current has to be “powered” by voltage, like from a battery. However, in a Josephson Junction, the tunneling that occurs between superconductor and insulator allows electrons to move without being “powered” by voltage. This leads to a so-called zero-voltage state, where cooper pairs tunnel through the insulator.

Electrons tunneling through the insulator isn’t new however. What made this experiment Nobel prize-worthy was that the laureates increased the current in this system until observing the appearance of a voltage. This was unexpected, as cooper-pairs are typically in a zero-voltage state, as mentioned before. Consequently, the only explanation these physicists were able to give this, is that the wave function of the entire system is tunneling through the insulator, not just the individual electron pairs.

Setting the tone for quantum computing

Thanks to this experiment (or series of experiments) quantum behavior was observed on a larger scale for the first time. Considering it was carried out in the 1980’s, when quantum mechanics’ applications weren’t clear yet, is remarkable. It set the tone for many of the technologies we are working on today, like quantum computing. The moral of the story is, we should stay tuned for the future of engineering using quantum mechanics, such as seen with the creation of those scanning tunneling microscopes. It might be an abstract field most of us will never understand, but let’s hope its effects will continue grace our lives.

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1. Nobel Prize in Physics 2025. (n.d.). NobelPrize.org. https://www.nobelprize.org/prizes/physics/2025/press-release/
2. Ross, & Sydney. (2025, October 21). John Dalton | Biography, Discoveries, Atomic Model, & Facts. Encyclopedia Britannica. https://www.britannica.com/biography/John-Dalton/Atomic-theory
3. Gawne, E. (2025, February 2). Splitting the atom: Why saying who was first is no easy task. https://www.bbc.com/news/articles/c93lk5ep5w0o
4. Libretexts. (2023, March 7). Tunneling. Chemistry LibreTexts.
5. The Nobel Committee for Physics. (2025, October 7). Scientific Background to the Nobel Prize in Physics 2025. Retrieved October 27, 2025, from https://www.nobelprize.org/prizes/physics/2025/advanced-information/

Footnotes:

1. For the purpose of this blog post, I simplified a lot. The Schrödinger equation itself does not directly give you the probability of an electron. However, considering that the math involved in quantum physics is complex, I might make a separate blog post elaborating on this. Here is an interesting video (from Domain of Science) on quantum wave functions that explains this phenomenon more closely and precisely. ↩︎