2025 Nobel Prize in Physics awarded for macroscopic quantum tunneling
The 2025 Nobel Prize in Physics has been awarded to John Clarke, Michel H. Devoret, and John M. Martinis for their discovery of macroscopic quantum tunneling and energy quantization in an electrical circuit. Their work, conducted in the 1980s at the University of California, Berkeley, demonstrated quantum effects on a macroscale using a Josephson junction. The laureates will share $1.1 million, with the ceremony set for December 10, 2025, in Stockholm.
In the early 20th century, physicists uncovered quantum mechanics, where subatomic particles exhibit behaviors like tunneling through energy barriers, defying classical physics. Building on this, Clarke, Devoret, and Martinis extended these effects to macroscopic scales. Clarke, who joined UC Berkeley's faculty in 1969 after his PhD from the University of Cambridge, collaborated with Devoret as a postdoc and Martinis as a graduate student in the mid-1980s.
The team used a Josephson junction—a device with two semiconductors separated by an insulator, allowing electron tunneling at low temperatures to form superconducting Cooper pairs. They built a one-centimeter microchip oscillator, akin to a quantum pendulum, and reduced noise to measure tunneling. By feeding current into the junction and observing voltage, they found that at very low temperatures, the system became superconducting, with current independent of temperature—a signature of macroscopic quantum tunneling.
They also confirmed quantized energy levels in the junction, limiting energy to discrete values like subatomic particles. This created a macroscopic quantum state described by a single wave function across billions of Cooper pairs, functioning as an artificial atom and rudimentary qubit.
"To put it mildly, it was the surprise of my life," Clarke said during the announcement press conference. "Our discovery in some ways is the basis of quantum computing."
The Nobel committee highlighted opportunities for quantum cryptography, computers, and sensors. Irfan Siddiqi, UC Berkeley physics chair, called it "the grandfather of qubits," enabling modern superconducting qubits like the 2007 transmon.
Martinis joined Google's quantum efforts in 2014, contributing to 2019's quantum supremacy claim, before co-founding Qolab in 2022. Devoret leads Google's quantum division and teaches at UC Santa Barbara, while Clarke is professor emeritus at UC Berkeley.
"These systems bridge the gap between microscopic quantum behavior and macroscopic devices," said Gregory Quiroz of Johns Hopkins. Jonathan Bagger of the American Physical Society noted the prize shows the value of fundamental research investments.