In Stockholm, on October 7, 2025, the Royal Academy of Sciences honors John Clarke), Michel H. Devoret, and John M. Martinis for revealing, in superconducting circuits, the quantum tunneling effect and energy quantization on a macroscopic scale. Their foundational experiments in the 1980s paved the way for transmon-type superconducting qubits and derivatives and applications in computing, sensors, and cybersecurity, laying the groundwork for a new industry.
Nobel Prize in Physics 2025: What the Announcement Means
On October 7, 2025, the Royal Swedish Academy of Sciences awarded the Nobel Prize in Physics to John Clarke, Michel H. Devoret, and John M. Martinis, awarded the 2025 Nobel Prize in Physics to the laureates John Clarke, Michel H. Devoret, and John M. Martinis. Reason: for demonstrating, using superconducting circuits at the heart of quantronics, that quantum phenomena, quantum tunneling effect and energy quantization, manifest on a macroscopic scale. In short: electrical setups that have become true "artificial atoms," observable and controllable in the laboratory. The Academy mentions concrete prospects for the next generation of quantum technologies: computers, sensors, and cryptography.
Official Affiliations (Nobel release): John Clarke (University of California, Berkeley); Michel H. Devoret (Yale University, New Haven, United States); John M. Martinis (University of California, Santa Barbara).
"Quantum physics in action": behind this phrase is the idea that the phase of a Josephson junction behaves quantumly. This key element of superconducting circuits is a macroscopic quantity with energy quantization with discrete levels. Moreover, it allows the possibility of crossing a barrier by quantum tunneling effect.
For the public, the most striking image remains that of a wall being crossed. Indeed, a ball does not have the energy to jump over the obstacle. However, in the quantum realm, it appears on the other side with a small probability. The laureates transposed this intuition into circuits, opening a lineage that leads to transmon-type superconducting qubits and derivatives.
Nobel Prize in Physics 2025 Laureates: What They Demonstrated
In the mid-1980s, two landmark experiments took place. In a current-biased Josephson junction, the Martinis–Devoret–Clarke team measured the escape rate from the zero-voltage regime to non-zero-voltage: a macroscopic quantum tunneling. A few weeks earlier, the same researchers signed the first observation of quantized energy levels for the phase. This phase is a collective variable of a circuit. These results establish that a macroscopic degree of freedom obeys quantum laws.
Milestones:
- October 7, 1985: demonstration of energy level quantization in a Josephson junction under microwaves. — Phys. Rev. Lett. 55(15): 1543–1546, published on October 7, 1985 (Energy-Level Quantization in the Zero-Voltage State of a Current-Biased Josephson Junction).
- October 28, 1985: measurement of macroscopic quantum tunneling in the underdamped regime. — Phys. Rev. Lett. 55(18): 1908–1911, published on October 28, 1985 (Measurements of Macroscopic Quantum Tunneling in a Josephson Junction).
These papers become classics and irrigate an entire field: superconducting quantum circuits, nonlinear oscillators, and readout methods. Later, they influence error correction codes applied to resonators and so-called "cat" qubits.
How a Circuit Becomes an "Artificial Atom"
The Josephson junction, two superconductors separated by a nanometric barrier, is the basic building block. At very low temperatures, the phase of the collective wave function acts as a coordinate. The washboard potential creates wells where the phase is trapped with discrete levels. Two mechanisms govern the exit from the well:
- Thermal activation (classical), dominant at "high" temperature.
- Quantum tunneling effect (quantum) at low temperature, causing a stochastic jump to the conductive state (appearance of a measurable voltage).
By exciting the circuit with microwaves, resonant transitions between levels are induced. The signature: a variation in the escape rate when the energy provided matches the gap between two levels. It is this spectroscopy that, in 1985, provided the experimental proof.
From Laboratories to Superconducting Qubits
The lineage with superconducting circuits is direct. The qubits of so-called superconducting quantum computing (charge, phase, flux) are born from these ideas; they will evolve into the transmon, a design that attenuates charge noise by shunting the junction with a large capacitance.
Two notions make the link:
- Josephson non-linearity: it creates non-equidistant levels, a condition to selectively address a qubit (states |0⟩ and |1⟩) within an oscillator.
- Microwave engineering: cavities, transmission lines, tunable couplings, and parametric amplifiers organize the readout and control at the gigahertz scale.
In the industry, these qubits have spread. John M. Martinis led the Google Quantum AI effort until 2020. Michel H. Devoret, a figure at Yale, trained a generation of researchers on superconducting qubits and "cat" qubits. John Clarke, at Berkeley, advanced SQUIDs, magnetometers of extreme sensitivity, and largely inspired detection architectures.
What Is This Nobel For? Applications and Challenges
- Quantum computing: superconducting processors targeting hybrid algorithms (chemistry, optimization, materials). Debates focus on decoherence, scaling, and energy cost.
- Sensors: SQUIDs (superconducting quantum interference devices) detect infinitesimal magnetic fields, useful in neuroimaging, geophysics, or fundamental physics (search for the axion).
- Cybersecurity: post-quantum cryptography (PQC) is classical but designed to withstand quantum computers; quantum key distribution (QKD) and quantum random number generators (QRNG) rely on measurable physical quantum phenomena.
Ecological impact: milli-kelvin cryostats and associated electronics have a real energy cost. Sobriety will come through more noise-tolerant architectures, more efficient refrigerators, and uses where the gain (optimization, low-carbon materials) offsets the footprint. As a rough order of magnitude, a 4 K cryostat consumes about 7 kW of electricity, and dilution refrigerators to reach milli-kelvins can exceed this figure depending on the architecture (source: Bluefors, 2024).
Portrait: From Saclay to Yale, the Journey of a French Pioneer
Michel H. Devoret, born in 1953 in Paris, trained in France, built bridges between Saclay, Berkeley, and Yale. Co-author of the 1985 experiments, he contributed to making superconducting circuits a toolbox for quantum mechanics: electron pumps, Josephson amplifiers, transmon, cat qubits. His hallmark: a pedagogy of "quantronics", this landscape where currents and voltages become quantum.
At Berkeley, John Clarke, a pioneer of SQUIDs, has durably shaped detection and instrumentation. At Santa Barbara, John M. Martinis transformed the proof of concept into experimental platforms, up to industrial prototypes.
France in the Race
The distinction resonates in France, where the quantum ecosystem has been structured: national programs, European funding, the rise of start-ups (analog computing, simulators, sensors). Training, schools, and laboratories remain an asset, but the challenge is still scaling up: talents, cryogenic supply chains, low-noise electronics, and interoperability with the cloud.