Three 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 a scale large enough to be seen. John Clarke, Michel H. Devoret, and John M. Martinis demonstrated that an electrical circuit, a macroscopic object by quantum standards, could exhibit bizarre behaviors like tunneling through energy barriers and having discrete energy levels, phenomena previously thought to be confined to the microscopic realm of single atoms. Their work directly enabled the creation of the superconducting quantum bits, or qubits, that are the fundamental components of today’s most powerful quantum computers.
The Royal Swedish Academy of Sciences in Stockholm awarded the prize of 11 million Swedish kronor, equivalent to more than $1.1 million, to the trio for their discovery of “macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.” This research established that the counterintuitive principles of quantum mechanics are not limited by size, laying the groundwork for technologies that harness these effects for computation and simulation. The laureates’ findings provided the first concrete evidence that a fabricated device involving billions of particles could collectively behave as a single quantum entity, now often referred to as an “artificial atom.”
Revealing Quantum Effects at Macro Scale
The foundational experiments took place at the University of California, Berkeley, in 1984 and 1985. At the time, the prevailing view was that quantum effects were fragile and observable only in microscopic systems like individual atoms or particles. Clarke, Devoret, and Martinis challenged this by constructing a special type of electrical circuit built around a device called a Josephson junction. A Josephson junction consists of two superconducting materials separated by a very thin insulating layer. In superconductors, electrons pair up and can move without any electrical resistance, behaving collectively as a single quantum entity described by a unified wave function.
The team’s key achievement was observing two distinct quantum phenomena in this circuit, which was large enough to be held in one’s hand. First, they demonstrated macroscopic quantum tunneling. This is a process where a quantum system can pass through a high-energy state that it classically should not have enough energy to overcome, akin to a ball rolling through a hill instead of over it. In their experiment, the circuit tunneled between a state with no voltage and a state with a measurable voltage. Second, they showed that the system’s energy was quantized, meaning it could only absorb or emit energy in discrete packets, or quanta, just as the electrons in an atom do. This confirmed the circuit behaved like an artificial atom with distinct energy levels.
The Laureates and Their Contributions
The Nobel Prize recognizes the collaborative work of three scientists whose careers have been central to the fields of quantum physics and superconductivity. John Clarke, a professor at the University of California, Berkeley, expressed that the basis of quantum computing relies significantly on their discovery. Michel H. Devoret, a professor at Yale University and the University of California, Santa Barbara, conducted seminal design work on these artificial atoms beginning in the 1980s. John M. Martinis, also of the University of California, Santa Barbara, later utilized these principles in quantum computer experiments, using the circuit’s quantized states as the zeros and ones of a qubit.
Devoret, born in France, began his influential work in Clarke’s lab at UC Berkeley in the 1980s before establishing his own research group. He is a leading figure in quantum technologies and a key member of the Co-design Center for Quantum Advantage (C2QA), a national quantum research center led by Brookhaven National Laboratory. Martinis would go on to lead Google’s quantum computing effort, where his team in 2019 controversially claimed to have achieved “quantum supremacy,” a milestone where a quantum computer performs a task impractical for any classical supercomputer. The shared prize highlights their interconnected and foundational contributions that bridged the gap between theoretical quantum mechanics and practical, engineered quantum systems.
From Artificial Atoms to Quantum Machines
The prizewinning work created a robust platform for controlling and manipulating quantum states, which is the essence of quantum computing. By demonstrating that a superconducting circuit could have discrete energy levels, the laureates provided a new physical system for building qubits. A qubit is the quantum analogue of a classical computer bit. While a classical bit is either a 0 or a 1, a qubit can exist in a superposition of both states simultaneously, and multiple qubits can be linked through a phenomenon called entanglement.
These properties allow quantum computers to explore a vastly larger computational space than classical computers, giving them the potential to solve certain classes of problems exponentially faster. The artificial atoms created by Clarke, Devoret, and Martinis are one of the leading technologies for building these powerful machines. In this architecture, the circuit’s lowest energy state can represent a ‘0’ and the next highest energy state can represent a ‘1’. Microwave pulses can be used to precisely control the qubit, putting it into a superposition or flipping its state. Today, technology companies and university labs around the world use circuits nearly identical to the ones from the 1980s experiments as the building blocks for their quantum processors.
Impact and Future of Quantum Technology
Paving the Way for Fault-Tolerant Computing
The discovery was not just a scientific curiosity; it was a foundational step toward building scalable, useful quantum machines. One of the greatest challenges in the field is overcoming the fragility of quantum states, which are easily disturbed by their environment, a phenomenon known as decoherence. The laureates’ work enabled the development of superconducting qubits that have become progressively more coherent over the decades. More recently, this technology has been central to demonstrating quantum error correction, a crucial technique for building fault-tolerant quantum computers that can function reliably despite environmental noise. Devoret himself led a research team that achieved a key milestone in quantum error correction, pushing the technology beyond the break-even point where the correction process is more effective than the errors it is designed to fix.
Applications and Broader Significance
The ability to create and control macroscopic quantum systems has applications beyond computing. These artificial atoms can be used as sensitive detectors for minute electromagnetic fields or to simulate other complex quantum systems, aiding fundamental scientific understanding. Olle Eriksson, chair of the Nobel Committee for Physics, noted that the work shows how “century-old quantum mechanics continually offers new surprises.” The prize underscores the enormous utility of quantum mechanics, which forms the bedrock of all digital technology. As researchers continue to build larger and more stable quantum systems, the discoveries made by Clarke, Devoret, and Martinis will remain central to a technological revolution with the potential to impact everything from medicine and materials science to cryptography and artificial intelligence.