Physics Today online now has reported the winners of the Physics Nobel Prize for 2025. This is for their landmark work in quantum mechanical tunneling and energy quantization in an electric circuit.
According to the report:
John Clarke of the University of California (UC), Berkeley, Michel Devoret of Yale University and UC Santa Barbara, and John Martinis of UC Santa Barbara are to be awarded the 2025 Nobel Prize in Physics “for the discovery of macroscopic quantum mechanical tunnelling and energy quantization in an electric circuit,” the Royal Swedish Academy of Sciences announced on Tuesday. Through experiments performed at UC Berkeley in 1984 and 1985, the laureates documented the observation of two fundamental quantum mechanical behaviors in a superconducting electrical system that contained billions of Cooper pairs of electrons—extending the realm of quantum phenomena to a scale at which they can be harnessed and put to work.
“We sometimes talk about quantum 1.0 and quantum 2.0: The first quantum revolution was in the early 20th century, trying to understand what happens at the tiniest scale of individual atoms,” says Robert Schoelkopf of Yale. “Quantum 2.0 is the idea that the more explicit parts of quantum mechanics, the weird parts like superposition and entanglement, are actually a resource that you could use in information-processing tasks, in sensing, in communications.” The work of Clarke, Devoret, and Martinis, he says, “is the root of quantum 2.0.”
The experiments—conducted when Martinis was a doctoral student and Devoret was a postdoc in Clarke’s lab—were performed with a device known as a Josephson junction, in which two superconductors are separated by a thin insulating barrier. Anthony Leggett had theorized that at extremely low temperatures, macroscopically distinct states of the superconductors could exhibit the quantum mechanical behavior of tunneling: jumping from one side of an energy barrier to another, something not possible in classical physics.
Throughout the early 1980s, attempts were made to observe the effect. With careful control of their experiment and reduction of noise, the Berkeley researchers were able to observe not only quantum tunneling but also the quantization of the allowed energy levels in the system. At millikelvin temperatures, the Cooper pairs move through the barrier at a rate aligned with theoretical predictions of quantum tunneling for the quantized states.
Those observations laid the foundations for the practical use of quantized states in the form of qubits. The circuits in superconducting qubits, one of the several types of qubits in development, also use Josephson junctions. “Quantum computing is having a bit of a moment,” says MIT’s Kyle Serniak, who earned his PhD in Devoret’s group at Yale. He explains that the recent demonstration of quantum error correction by the Google Quantum AI team, for which Devoret is chief scientist of quantum hardware, is a significant step toward the realization of a useful quantum computer based on superconducting qubits.
“They were able to put more and more qubits together, run this error-correction algorithm, and see that even as the system got bigger, the logical error rates decreased,” Serniak says. Though that milestone was achieved with superconducting qubits, other qubit designs, like trapped ions and stable atoms, are also at the leading edge of quantum computing advances. Applications envisioned for quantum computing include cryptography, drug discovery, and modeling of complex physical systems.
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