The 2025 Nobel Prize in Physics Goes to Researchers Who Showed Quantum Tunneling on a Chip
John Clarke, Michel H. Devoret and John M. Martinis shared the 2025 Nobel Prize in Physics for their work showing how bizarre microscopic quantum effects can infiltrate our large-scale, everyday world
The 2025 Nobel Prize in Physics
In the 100th-anniversary year of quantum mechanics, which describes the universe at its smallest, most fundamental scales, the 2025 Nobel Prize in Physics has gone to three pioneers in bringing its mysterious effects into the everyday world.
Quantum tunneling occurs when a particle passes directly through an otherwise impassable barrier to appear on the other side. This is akin to throwing a ball at a wall and, rather than seeing it bounce back, finding it unscathed on the other side with the wall itself fully intact. The effect is the basis for transistors, yet it usually diminishes for assemblages of many particles—which is why you never see anyone phasing through walls and floors in everyday life. But in a series of experiments performed at the University of California, Berkeley, in 1984 and 1985, Clarke, Devoret and Martinis showed that the process could occur at larger scales than previously thought possible. (Relatedly, Clarke also penned an essay for Scientific American in 1994 on superconducting quantum interference devices, or SQUIDS, highly sensitive magnetometers used in medical diagnostic equipment and other high-performance hardware.)
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“It’s worth remembering that for most of the 100-year history of the field, quantum theory was thought of as the theory of the very small,” says Aephraim Steinberg, a physicist at the University of Toronto, who studies quantum tunneling. The experiments of Clarke, Devoret and Martinis constitute “some of the first evidence that quantum mechanics appears to describe not just the world of the very small but even the ‘mesoscopic’ world of billions and billions of electrons—and potentially our larger world as well.”
Inspired by the theoretical work of the physicist (and eventual Nobel laureate) Anthony Leggett, their experiments relied on electronic circuits built from superconductors, which can conduct current with no electric resistance. The resulting electronic chip–like devices, which the Nobel Committee noted in a statement were “big enough to be held in the hand,” contained superconducting components divided by a thin barrier of nonconductive material. This arrangement is known as a Josephson junction, after the Nobel Prize–winning work of British theoretical physicist Brian Josephson, who first proposed it in the early 1960s. Through exhaustive mapping and measurement of the circuit’s properties, Clarke, Devoret and Martinis were able to show how electrons moving through the system act as if they are a single particle, tunneling across the dividing barrier to fill the entire circuit.
Their experimental system only exhibited two distinct modes—one in which the current was “trapped” in a zero-voltage state and another in which the current escaped this state via tunneling to show a voltage. This clearly demonstrated the quantized nature of the system, in which only a specific amount of energy could be emitted or absorbed, as predicted by quantum mechanics.
“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, in a statement announcing the award. “It is also enormously useful, as quantum mechanics is the foundation of all digital technology.”
The prize represents a triumph for the University of California system; Clarke remains at the University of California, Berkeley, and Devoret and Martinis are at the University of California, Santa Barbara. (Devoret also holds a position at Yale University.)
Reached on his cell phone by the Nobel Committee during the award’s announcement, the “completely stunned” Clarke noted that the phenomenon that’s now made him a Nobel laureate is also “one of the underlying reasons that the cell phone works” and that “our discovery, in some ways, is the basis of quantum computing.”
Quantum computers have the potential to profoundly increase the speed and efficiency of certain complex calculations far beyond what classical computers can achieve. Their power comes from quantum bits, or qubits, rather than the bits used in classical computing. Unlike bits, which encode information as a binary series of 0s and 1s, a qubit in superposition can encode not only 0 or 1 but also most any values in between. Accessing all those intermediate values requires holding a qubit in superposition—usually by cooling it to nearly absolute zero and shielding it from all manners of error-inducing environmental noise. Entangled ensembles of qubits can then be orchestrated to tackle ever-larger computational problems.
The frontier of the field is to harmonize sufficient numbers of robust, reliable qubits to create systems that clearly demonstrate “quantum advantage” over classical computing. Governments, research institutions and private companies around the globe are annually spending tens of billions of dollars in pursuit of quantum advantage, with most systems reliant upon superconducting qubits that owe their existence, in part, to Clarke, Devoret and Martinis’s groundbreaking research.
“As you start to concatenate many qubits together, questions arise: How big can quantum entanglement be? How big of a quantum system can you make?” says Irfan Siddiqi, a quantum information scientist at the University of California, Berkeley, who has worked closely with all three of the new laureates. “And much of this new wave of research is based on [the laureates’] earlier answering of this more fundamental question of whether a macroscopic system could be quantum mechanical.”
For their work, which the Nobel citation describes as “the discovery of macroscopic quantum tunneling and energy quantization in an electric circuit,” the researchers will split equally a prize of 11 million Swedish kronor (about $1.17 million). This is a princely sum—but also a pale shadow of the almost incalculable profits that could accrue if or when the lofty promise of quantum computing they helped catalyze at last is fulfilled.
Lee Billings is a science journalist specializing in astronomy, physics, planetary science, and spaceflight, and is a senior editor at Scientific American. He is the author of a critically acclaimed book, Five Billion Years of Solitude: the Search for Life Among the Stars, which in 2014 won a Science Communication Award from the American Institute of Physics. In addition to his work for Scientific American, Billings’s writing has appeared in the New York Times, the Wall Street Journal, the Boston Globe, Wired, New Scientist, Popular Science, and many other publications. Billings joined Scientific American in 2014, and previously worked as a staff editor at SEED magazine. He holds a B.A. in journalism from the University of Minnesota.
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