Three American physicists have been awarded the 2025 Nobel Prize in Physics for a series of experiments in the 1980s that revealed the strange rules of quantum mechanics at work in a tangible, human-made object. Their discovery that an electrical circuit could exhibit quantum behaviors, such as existing in two energy states at once, shattered the long-held assumption that the bizarre nature of the quantum world was confined to subatomic particles. This work provided the first concrete evidence of macroscopic quantum phenomena, directly enabling the development of the powerful quantum computers now being pursued by global technology giants.
The Royal Swedish Academy of Sciences in Stockholm awarded the prize jointly to John Clarke of the University of California, Berkeley; Michel H. Devoret of Yale University; and John M. Martinis, of the University of California, Santa Barbara, and formerly of Google. The laureates will share the 11 million Swedish krona prize for their foundational work on “the discovery of macroscopic quantum mechanical tunneling and energy quantization in an electric circuit.” By engineering a superconducting device large enough to be seen, they built a bridge between the microscopic quantum realm and our everyday world, a breakthrough that forms the bedrock of modern quantum information science.
From Theory to Tangible Circuits
For much of the 20th century, quantum mechanics described a world profoundly at odds with human experience. It depicted a reality where particles could be in multiple places simultaneously and tunnel through impenetrable barriers. Physicists generally believed these counterintuitive effects were delicate phenomena that washed out on any scale larger than an atom. It was thought that in large objects, composed of countless interacting particles, these distinct quantum signatures would be averaged away, leaving only the predictable certainty of classical physics. A thrown ball, for instance, follows a predictable arc, and it will never tunnel through a wall.
The laureates challenged this conventional wisdom. Working at UC Berkeley in the 1980s, they designed an experiment to see if a collective system, involving billions of electrons, could be coaxed into behaving like a single quantum entity. Their work sought to answer a fundamental question: could quantum mechanics be directly observed and controlled in an engineered system? Success would mean that quantum weirdness was not just a feature of the universe’s smallest components but a property that could be harnessed for new technologies. This line of inquiry moved quantum theory from the blackboard to the laboratory workbench, setting the stage for a technological revolution.
Engineering an ‘Artificial Atom’
The breakthrough centered on a device known as a Josephson junction. This component consists of two strips of superconducting material separated by an extremely thin insulating barrier. In a superconductor, which is a material cooled to temperatures near absolute zero, electrons pair up into “Cooper pairs” and move in a collective, synchronized state without any electrical resistance. This unified quantum state is crucial; it means that billions of electron pairs can be described by a single, shared wavefunction, allowing them to act in concert as one coherent entity.
Observing the Quantum Leap
The team’s experiments demonstrated two distinctively quantum phenomena. First, they observed macroscopic quantum tunneling. They prepared the circuit in a low-energy state, trapped behind an energy barrier that, according to classical physics, it should not have been able to surmount. Yet, the system repeatedly escaped this trap, providing the first unambiguous evidence that the entire circuit—a macroscopic object—was “tunneling” through the energy barrier in a way only predicted by quantum mechanics.
Measuring Quantized Energy
In a second, decisive experiment, the researchers exposed the circuit to microwave radiation. They found that the circuit absorbed energy only at specific, discrete frequencies, creating sharp peaks in their measurements. This was the smoking gun for energy quantization. Just as an electron in an atom can only occupy specific energy levels and “jumps” between them, their circuit, containing billions of particles, was behaving as a single artificial atom with its own distinct energy ladder. They had effectively built a macroscopic object that obeyed the fundamental quantum rule of discrete energy states.
The Foundation of Quantum Computing
The laureates’ demonstration that a macroscopic circuit could have quantized energy levels and be manipulated with microwaves established the core principles of the superconducting quantum bit, or qubit. A qubit is the fundamental unit of a quantum computer, analogous to the binary bit in a classical computer. While a classical bit can be only a 0 or a 1, a qubit can exist as a 0, a 1, or a superposition of both states simultaneously. The two lowest energy levels of the laureates’ artificial atom serve as the 0 and 1 states of the modern superconducting qubit.
Their work proved that these quantum states could be engineered, controlled, and measured, laying the intellectual and practical groundwork for quantum computation. As laureate John Clarke stated, “The basis of quantum computing relies to quite an extent on our discovery.” Decades after their initial experiments, this fundamental technology is now used in the prototype quantum computers being developed by IBM, Google, and other research institutions worldwide. These machines hold the potential to solve problems far beyond the capacity of even the most powerful supercomputers, with applications in medicine, materials science, and cryptography.
A New Door to the Quantum World
The 2025 Nobel Prize in Physics honors a discovery that fundamentally changed scientists’ relationship with the quantum realm. It transformed quantum mechanics from a passive description of the microscopic world into a set of instructions for building new technologies. By proving that quantum effects could be scaled up, the laureates provided the tools for others to manipulate the quantum world directly.
Eva Olsson, a member of the Nobel Committee for Physics, described the discovery as having opened “a door to another world.” She explained that bringing quantum phenomena to a visible scale allows scientists to handle, control, and study them in unprecedented ways. The work of Clarke, Devoret, and Martinis did more than confirm a surprising prediction of physics; it launched a new era of applied quantum science. Their experiments provided the first glimpse of a world where the seemingly magical properties of quantum mechanics could be harnessed, forming the essential bridge between a century-old theory and the quantum technologies of the future.
