A simple explanation of the 2025 Nobel Prize in Physics
The winners of the 2025 Nobel Prize in Physics have been announced: John Clarke, Michel H. Devoret, and John M. Martinis! Their achievement lies in demonstrating quantum tunnelling and quantised energy levels on a macroscopic scale. The experiments were conducted using superconducting circuits. Here’s a quick overview of their work.
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An overview of quantum tunnelling and the scale-dependent properties of materials
Our bodies and the objects around us are made up of tiny particles such as electrons and atoms. In this microscopic world, it is well known that electrons and atoms behave according to the laws of quantum mechanics. Quantum mechanics allows for phenomena that go beyond our everyday intuition. One such phenomenon is quantum tunnelling.
Let’s consider an example using a tennis ball.
Imagine throwing a tennis ball at a wall repeatedly. In our everyday experience, the ball will never pass through the wall. In other words, we can confidently say that the probability of a tennis ball tunnelling through a wall is zero. However, according to quantum theory, at the scale of electrons and atoms, there is a finite probability that a particle can pass through such a barrier. This means that, in quantum mechanics, a particle can tunnel through a wall that would be impenetrable in classical physics.
In fact, quantum tunnelling has been observed in single particles and extremely small systems. But in sports like tennis or table tennis, which have been played around the world for decades, no one has ever seen a ball tunnel through the net or a wall.
This illustrates that as the scale of a system increases, quantum mechanical effects become much harder to observe.
About this year’s Nobel Prize in Physics
John Clarke, Michel H. Devoret, and John M. Martinis were awarded the Nobel Prize in Physics for demonstrating that quantum tunnelling can be observed at a macroscopic scale using superconducting circuits-a state unique to quantum mechanics. In other words, they were recognized for showing that strange phenomena usually confined to the microscopic world of quantum mechanics can appear in systems large enough to hold in your hand.
In their research, they proved that not just single particles, but billions of electrons can behave collectively like one giant particle, exhibiting tunnelling behavior-intuitively, as if passing through a wall.
They also confirmed that when microwaves of specific wavelengths were applied, the system absorbed and emitted energy in discrete levels, a hallmark of quantum mechanics where energy exists in quantised packets.
For example, the unit of energy is the joule (J). In our everyday intuition, we might think that between 1 J and 2 J, there can be values like 1.1 J, 1.2 J, 1.3 J, and so on-infinitely many possible values in between. However, in quantum mechanics, the states of matter cannot take on a continuous range of values; instead, only discrete, “quantized” values are allowed. This is another aspect that defies our common sense and feels quite mysterious.
Relation to Quantum Computing
Furthermore, John M. Martinis later applied this approach to research aimed at realizing superconducting quantum bits (qubits).
This research made use of the fact that the superconducting circuits described earlier possess discrete energy levels, a characteristic feature of quantum mechanics.
In order to function as quantum bits-similar to the bits used in classical computers-each qubit must be able to transition between two states: 0 and 1. Martinis successfully used the lowest energy state and the next higher energy state of the superconducting circuit to represent 0 and 1, respectively.
Companies like IBM, Google, and Rigetti have developed practical quantum computers based on superconducting circuits. It is no doubt that the realization of today’s large-scale quantum computers has been made possible by demonstrating quantum mechanical behavior on such a macroscopic scale.
References
Amazon Braket Learning Course
I have also created a learning course on Amazon Braket, AWS’s quantum computing service.
This course is designed for those with no prior knowledge of quantum computing or AWS, and by the end, you’ll even be able to learn about quantum machine learning. Take advantage of this opportunity to build your skills in quantum technologies!