Three physicists have been awarded the 2025 Nobel Prize in Physics for a series of pioneering experiments in the 1980s that revealed that the strange rules of quantum mechanics are not confined to the microscopic world of atoms and can govern the behavior of large, human-made electrical circuits. The Royal Swedish Academy of Sciences honored John Clarke, Michel H. Devoret, and John M. Martinis for their work, which fundamentally shifted the understanding of physics and laid the groundwork for today’s quantum technologies, including the powerful quantum computers now being developed.
Their discovery challenged the long-held belief that quantum effects vanish at larger scales. Working at the University of California, Berkeley, the trio demonstrated for the first time that phenomena such as quantum tunneling and quantized energy levels could be observed in a superconducting circuit—a device large enough to be held in one’s hand. This breakthrough bridged the gap between the subatomic realm and the macroscopic world, and in doing so, it opened the door to engineering complex systems that operate on quantum principles, from ultra-sensitive sensors to the superconducting qubits that are the building blocks of quantum computers.
Bringing the Quantum World to a Human Scale
For decades, the counterintuitive principles of quantum mechanics—where particles can exist in multiple states at once or tunnel through impenetrable barriers—were considered exclusive to the realm of individual atoms and subatomic particles. It was widely assumed that in larger, more complex systems, these delicate effects would be washed out by classical physics. The work of Clarke, Devoret, and Martinis overturned this assumption by proving that a collective system involving trillions of particles could exhibit coherent quantum behavior.
Their experiments, conducted between 1984 and 1985, centered on a specially designed electrical circuit cooled to extremely low temperatures to become a superconductor, a state where electricity flows without resistance. By meticulously building and measuring this system, they provided the first definitive proof that the entire circuit, as a single entity, obeyed the laws of quantum mechanics. This discovery of “macroscopic quantum tunneling” showed that the boundary between the quantum and classical worlds was not as clear-cut as previously thought, confirming that quantum reality could be observed and manipulated on a tangible scale.
The Foundational Physics Explained
Quantum Tunneling in a Circuit
One of the most bizarre predictions of quantum mechanics is tunneling, where a particle can pass through a barrier that it classically should not have enough energy to overcome. This is analogous to a ball appearing on the other side of a solid wall without having been thrown over it. Before the laureates’ research, this phenomenon had only been observed with single particles like electrons. The team designed an experiment using a device called a Josephson junction, which consists of two superconducting materials separated by a thin, non-conducting layer. They demonstrated that groups of paired electrons, known as Cooper pairs, could collectively “tunnel” across this insulating barrier in a coherent way, causing the entire circuit to jump between different states as a single quantum object.
Observing Quantized Energy
A central tenet of quantum mechanics is that energy is “quantized,” meaning a system can only possess energy in discrete, indivisible packets, or levels. For example, an atom can have an energy of 1 or 2, but never 1.5. The laureates were able to prove that their macroscopic circuit also possessed these distinct energy levels, just as a single atom does. They observed that the circuit would only absorb or release energy in these specific, fixed amounts. This was a landmark achievement, as it showed that a complex, engineered object behaved according to the same fundamental quantum rules that govern the simplest building blocks of nature.
From Basic Research to a Technological Revolution
The groundbreaking experiments conducted by the trio at UC Berkeley laid an essential foundation for the second quantum revolution—the ongoing effort to build and commercialize quantum technologies. At a press conference, Clarke noted that at the time of the discovery, the team was absorbed in understanding the fundamental physics and had not envisioned the immense practical impact their work would eventually have. That fundamental understanding, however, proved to be the critical missing piece needed to control and engineer quantum systems.
The Birth of Superconducting Qubits
The principles demonstrated by the laureates are the direct scientific ancestors of the superconducting qubits used by leading technology companies in the race to build a functional quantum computer. A qubit, or quantum bit, is the basic unit of quantum information. Superconducting circuits based on the laureates’ designs are an ideal platform for qubits because they are large enough to be fabricated and controlled using established microchip techniques, yet they remain coherent quantum systems. Martinis himself later led the Google Quantum AI lab that, in 2019, announced the achievement of “quantum supremacy”—a demonstration that a quantum computer could perform a specific calculation that is effectively impossible for even the most powerful classical supercomputers.
New Frontiers in Sensing and Measurement
Beyond computing, the ability to create and control macroscopic quantum states has enabled the development of exquisitely sensitive measurement devices. Josephson junctions, the core component of the Nobel-winning experiments, are now used in sensors capable of detecting minuscule magnetic fields. These quantum sensors have applications in fields ranging from medical imaging and materials science to fundamental physics research. The laureates’ work provided the blueprint for harnessing the collective quantum behavior of circuits for practical purposes.
The Laureates and Their Legacy
The 2025 Nobel Prize in Physics, along with its prize of 11 million Swedish kronor (approximately $1.17 million), will be shared equally among the three scientists whose collaboration was pivotal. John Clarke is a professor at the University of California, Berkeley. Michel H. Devoret, who was a postdoctoral researcher at the time of the discovery, is now a professor at Yale University and UC Santa Barbara. John M. Martinis, then a Ph.D. student in Clarke’s lab, is now an emeritus professor at UC Santa Barbara.
Their work fundamentally reshaped the landscape of modern physics. Olle Eriksson, chair of the Nobel Committee for Physics, stated, “It is wonderful to be able to celebrate the way that century-old quantum mechanics continually offers new surprises.” By demonstrating that the quantum world was not locked away at the atomic scale, the laureates gave scientists and engineers the tools to build a new generation of technologies that were once the exclusive domain of science fiction.