The 2025 Nobel Prize in Physics rewards the direct application of quantum physics in practical devices.
The 2025 Nobel Prize in Physics has crossed the Atlantic, from Stockholm to the United States, to honour three scientists for “an electrical circuit in which they demonstrated both quantum mechanical tunnelling and quantised energy levels in a system,” as stated by the Nobel Committee.
John Clarke (University of California, Berkeley), Michel Devoret (Yale University and the University of California, Santa Barbara) and John Martinis (University of California, Santa Barbara) were the 2025 laureates of the Royal Swedish Academy of Sciences.
In an article published on the day of the award ceremony, 7 October, the Financial Times quoted several remarks made by members of the Swedish Academy when the prize was announced; among them was the official justification already mentioned above, yet one statement helps us grasp the practical impact of the research that earned the three scientists this year’s Nobel Prize: according to the Nobel Committee, ““bizarre properties of the quantum world can be made concrete in a system big enough to be held in the hand.”
This is precisely the point that Ariel Guerreiro, a researcher at INESC TEC specialising in quantum physics, considered essential to highlight:
“The prize recognises a decisive moment in the history of modern physics: the experimental demonstration that the laws of quantum mechanics, traditionally associated with the microscopic world of atoms and particles, can also manifest themselves in systems large enough to fit in the palm of your hand.”
Adding to this, Luís Paulo Santos, an INESC TEC researcher in quantum computing, explained:
“Quantum mechanics predicts several phenomena that are typically detectable only at very small scales; for instance, at the level of molecules, atoms, or subatomic particles like electrons and photons. These quantum phenomena represent behaviours that cannot be described by classical physics, such as the fact that energy can only take on discrete, well-defined values, or that a group of particles can cross a barrier as if tunnelling through it. At scales larger than the molecular, these phenomena are usually not observable.”
The timeline of the discovery
In the mid-1980s, specifically between 1984 and 1985, John Clarke, Michel H. Devoret and John M. Martinis conducted a series of experiments at the University of California, Berkeley. They worked with electrical circuits composed of two superconductors separated by a thin insulating layer – a structure known as a Josephson junction.
“This system revealed, for the first time on a macroscopic scale, two fundamental quantum phenomena: the existence of quantised energy levels and the tunnelling effect through a potential energy barrier,” explained Ariel Guerreiro, who also lectures at the Faculty of Sciences of the University of Porto (FCUP).
Luís Paulo Santos, also a lecturer, but at the University of Minho, added that these experiments used superconducting materials cooled to temperatures very close to absolute zero.
“The key takeaway is that quantum phenomena are not confined to (sub)molecular scales but also occur at larger scales. Moreover, they can be controlled and measured using human-made devices. This opened the door to manipulating quantum states through artificial systems that behave like artificial atoms,” he mentioned.
Was the quantisation of electron energy levels a novel discovery?
“No,” said Ariel Guerreiro. “The quantisation of electron energy levels in atoms has been known since the early days of quantum mechanics and was one of the foundational principles. The quantum tunnelling effect was also identified as early as the 1930s, when scientists realised that certain atomic nuclei could emit alpha particles even without having enough energy to overcome the potential energy barrier confining them within the nucleus.”
So, what was the innovative aspect of the discovery made by these three scientists?
These quantum phenomena had previously only been observed in microscopic systems – at or below the scale of atoms – involving individual particles.
For much of the 20th century, the dominant view was that such effects could not manifest in macroscopic systems composed of vast numbers of particles.
“Many believed that tiny variations in the behaviour of each particle would add up in such a way as to erase any trace of quantum behaviour. At those scales, it was thought that physical systems should be described by classical mechanics – the theory that quantum mechanics replaced, but which was still assumed to govern the world at human scale,” explained Ariel Guerreiro.
The trio’s results showed that a collective degree of freedom involving billions of Cooper pairs – each made up of two strongly bound electrons – can behave as a single quantum particle.
“This finding reinforced the universal validity of quantum theory and became one of the first demonstrations of macroscopic quantum effects, which include phenomena such as superconductivity, superfluidity, and Bose–Einstein condensation – several of which have also earned Physics Nobel Prizes in the past,” added the INESC TEC researcher.
The practical applications of the 2025 Nobel discoveries
“Macroscopic quantum effects are key pillars of fundamental science and quantum physics,” said Ariel Guerreiro. The laureates demonstrated that said effects can be grasped, controlled, and measured – paving the way for technologies now central to debates around quantum computing.
“The results achieved by these Nobel laureates led, by the late 1990s, to the development of quantum bits (qubits) based on superconductors, whose states can be altered and measured. These qubits, incorporating countless advances since then, remain the fundamental components of today’s superconducting quantum computers,” explained Luís Paulo Santos.
Qubits are the basic units of information storage and processing in quantum computers, playing a role like that of transistors in classical computers.
“Among the various possible technologies for implementing qubits, superconducting circuits stand out because their fabrication processes are similar – though not identical – to those used in conventional microelectronics. This ‘technological affinity’ has allowed faster progress in developing superconducting quantum circuits,” emphasised Ariel Guerreiro.
One key advantage of this approach lies in scalability – the ability to integrate an ever-growing number of qubits on a single chip while maintaining control and quantum coherence.
“The number of integrated qubits has been increasing rapidly, currently reaching around 1,000. Beyond this threshold, quantum computers are expected to move beyond experimental demonstrations and begin solving problems of real scientific and technological relevance,” explained the researcher.
INESC TEC’s work in these areas
Two INESC TEC research areas have particularly benefited from the scientific advances made by the 2025 Nobel laureates: quantum computing, where Luís Paulo Santos works, and quantum physics, where Ariel Guerreiro carries out his research.
In northern Portugal (specifically in Braga, at the University of Minho), a team of INESC TEC researchers focuses on quantum computing, particularly the formal modelling of quantum circuits – including those based on superconducting qubits. Their work addresses crucial challenges such as reducing measurement costs, recycling quantum information in variational algorithms, and developing formal models and verification methods for quantum software – all fundamental for ensuring the correctness and robustness of future quantum processors.
Meanwhile, in Porto, at the Faculty of Sciences, Ariel Guerreiro has been conducting theoretical research on the persistence of quantum entanglement in macroscopic systems and proposing ways to generate it in optomechanical systems. His work demonstrates that the boundary between the quantum and classical worlds can also be explored within national research contexts. Notably, one of his projects in this field was carried out with Alain Aspect, the 2022 Nobel Laureate in Physics.
The 2025 Nobel Prize in Physics celebrates not only a milestone in the foundations of quantum mechanics but also a profound technological impact. “It represents, in exemplary fashion, a vision deeply shared by INESC TEC: that fundamental science and technological innovation are inseparable parts of the same process of discovery. It is this integrated, forward-looking vision that guides the Institute’s research – a journey that spans the entire spectrum of knowledge, from understanding to building, connecting scientific curiosity with the ability to turn ideas into technology,” concluded Ariel Guerreiro.
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