2025-Nobel Prize in Physics for Quantum Tunnelling

Quantum mechanics says that particles can sometimes cross barriers they don’t have the energy to climb, like boring through a mountain instead of scaling it first. This process, called tunnelling, is common in nuclear and atomic physics. One of the mind-boggling behaviours that particles are capable of here is “tunnelling”, literally, the ability of particles to pass through physical walls. It is as if a cricket ball hitting the pitch will surely bounce up, but the odd cricket-ball particle will simply burrow into the ground. Such strange behaviour cannot be observed at the macroscopic level but scientists showed that it was possible to organise a multitude of single particles and coerce them to exhibit “tunnelling” properties.
Much like early insight into quantum mechanics paved the way for transistors and silicon chips in the 1950s, the trio Nobel laureate in Physics of 2025, devised an electrical circuit with two superconductors, components that can conduct a current without any electrical resistance. They separated these with a thin layer of material – called a Josephson junction — that did not conduct any current at all. In this experiment, they showed that they could control and investigate a phenomenon in which all the charged particles in the superconductor behave in unison, as if they are a single ‘particle’ that fills the entire circuit. Following this, they were able to demonstrate that such a particle could be made to behave simulating the flow of electricity even without voltage, a prerequisite for the flow of current.
These were akin to the first ‘super-conducting circuits’ that could potentially realise practical, useful quantum computers and quantum sensors. Quantum computers, unlike contemporary computers, deal in ‘qubits’, rather than binary bits. This allows them to perform calculations exponentially faster but also threaten all kinds of encryption systems that are premised on bit-based computers taking the equivalent of forever to hack through the mathematical locks guarding security systems. Therefore, developing quantum-based computing system is a major research focus, including in India, which has a major National Quantum Computing Mission, that aims to build workable quantum computers by 2031.
Quantum tunnelling of individual quantum particles, for example electrons, was known before, but this work done in the mid-80s was a path-breaking demonstration of the power of quantum physics that eventually led to new technology,” said Arindam Ghosh, physicist at the Indian Institute of Science, Bengaluru, and researcher in the field of quantum technology “ This purely fundamental experimental research with Josephson junctions nearly 40 years ago is the pillar of today’s understanding and engineering of superconducting qubits that may very well make tomorrow’s quantum computers.”
The Nobel Prize for Physics this year will be awarded to three scientists — John Clarke, Michel Devoret and John Martinis, the Royal Swedish Academy of Sciences said on Tuesday. The three worked together and devised experiments to tease greater insight into the workings of the quantum world: the realm of the ultra-small when objects, broken down to single, constituent particles, cease to behave in the way we ordinarily expect them to. The 2025 physics Nobel Prize laureates John Clarke, Michel Devoret and John Martinis showed that such behaviour can occur not only in subatomic particles but also in an electrical circuit made of superconductors. The finding opens the door to new technologies set to transform the way we collect, study, understand, and use information from our surroundings.
John Clarke was a professor at the University of California, Berkeley, in the U.S., where he had moved after completing his doctoral degree at the University of Cambridge, U.K., in 1968. At UC Berkeley he built up his research group and specialised in exploring a range of phenomena using superconductors and the Josephson junction. By the mid-1980s, Michel Devoret had joined Clarke’s research group, after receiving his doctorate in Paris. This group also included the doctoral student John Martinis. Together, they took on the challenge of demonstrating macroscopic quantum tunnelling.
Because quantum states are sensitive to the slightest disturbance, vast amounts of care and precision were necessary to screen the experimental set-up from all the interference that could affect it. They succeeded in refining and measuring all the properties of their electrical circuit, allowing them to understand it in detail. The trio will equally share the prize of 11 million Swedish kroner, or about ¹ 1 crore.
“It is wonderful to be able to celebrate the way that century-old quantum mechanics continually offers new surprises. It is also enormously useful, as quantum mechanics is the foundation of all digital technology,” said Olle Eriksson, Chair of the Nobel Committee for
The fundamental unit of the award-winning experiments the trio conducted is a device called a Josephson junction. Here, two superconductors are separated by a very thin insulator. The trio wanted to know if a parameter of the circuit as a whole, in this case the junction’s phase difference, could behave like a single quantum particle. They came away from their experiments with a resounding ‘yes’, by observing both macroscopic quantum mechanical tunnelling and discrete energy levels in the circuit.
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