A fundamental question in physics asks: How large can a system be and still display quantum mechanical effects? The 2025 Nobel Prize in Physics answers that question. John Clarke, Michel H. Devoret, and John M. Martinis have been awarded the prize “for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.” Their ground-breaking experiments brought quantum mechanics from the microscopic world into the realm of objects visible — and even holdable — by human hands.
Bringing Quantum Mechanics to the Macroscopic World
Quantum mechanics, the theory that governs the behaviour of particles at atomic and subatomic scales, allows phenomena that defy classical intuition. One such phenomenon is quantum tunnelling, where a particle can pass directly through a barrier it should not, in classical terms, be able to cross.
Ordinarily, quantum effects become negligible when large numbers of particles are involved. However, Clarke, Devoret, and Martinis demonstrated that quantum behaviour can persist on a macroscopic scale — a revolutionary finding that reshapes how we think about the boundaries of quantum physics.
Pioneering Experiments with Superconducting Circuits
In 1984 and 1985, the laureates conducted a series of landmark experiments using an electronic circuit made of superconductors — materials that conduct electricity without resistance. The superconducting elements were separated by a thin non-conducting layer, forming what is known as a Josephson junction.
By meticulously refining the circuit and measuring its properties, they created a system where the movement of countless charged particles through the superconductor behaved as if they were a single quantum particle extending across the entire circuit. This “macroscopic quantum system” provided a unique platform to explore quantum phenomena at a scale far larger than individual particles.
Quantum Tunnelling: Breaking Through the Barrier
Initially, the system existed in a state where current flowed with zero voltage, seemingly trapped behind an energy barrier. Classical physics would predict it should remain stuck there. Yet, the experiment revealed a striking quantum effect: the system tunnelled through the barrier and transitioned into a new state, detectable by the emergence of a voltage.
This observation provided direct evidence of quantum tunnelling in a macroscopic system — a remarkable confirmation that quantum mechanics governs not just atoms and electrons but also larger, engineered structures.
Evidence of Energy Quantisation
The team also demonstrated that their macroscopic quantum system absorbed and emitted energy in discrete packets, or quanta — exactly as predicted by quantum theory. This quantised behaviour, long observed in atoms and molecules, was now confirmed in a system large enough to hold in one’s hand. The result showed that quantum principles apply far beyond the microscopic realm, blurring the line between the quantum and classical worlds.
Century-Old Theory, New Surprises
“It is wonderful to be able to celebrate the way that century-old quantum mechanics continually offers new surprises,” said Olle Eriksson, Chair of the Nobel Committee for Physics. “It is also enormously useful, as quantum mechanics is the foundation of all digital technology.” Indeed, today’s microchips — including the transistors powering computers and smartphones — rely on quantum principles. The laureates’ work now pushes the frontier toward next-generation quantum technologies, such as quantum cryptography, quantum computing, and quantum sensors.
Paving the Way for Future Quantum Technologies
Clarke, Devoret, and Martinis have made discoveries that go beyond a fundamental advance in physics — they provide a blueprint for future innovation. Their experiments demonstrate how scientists can harness and control quantum mechanics at scales suitable for practical devices. This work opens doors to powerful new technologies that will shape the coming decades.
2025 Physics Laureates
John Clarke – Born 1942 in Cambridge, UK. PhD (1968), University of Cambridge. Professor at the University of California, Berkeley, USA.
Michel H. Devoret – Born 1953 in Paris, France. PhD (1982), Paris-Sud University. Professor at Yale University and the University of California, Santa Barbara, USA.
John M. Martinis – Born 1958. PhD (1987), University of California, Berkeley. Professor at the University of California, Santa Barbara, USA.
A Landmark in Physics
According to the press release, the work of Clarke, Devoret, and Martinis has transformed our understanding of the quantum world. Their research proves that quantum mechanics governs not only the smallest particles. It also applies to engineered systems visible to the naked eye. Their discoveries bridge the gap between the quantum and classical worlds — and pave the way for revolutionary technologies that will shape the future.
