For decades, our computers have been advancing by packing more and more transistors onto a single chip. But this race has its physical limits: we cannot reduce the size of components indefinitely. To push the boundaries further, scientists are exploring a radically different path: harnessing the laws of quantum physics—the laws that govern the behavior of matter at the atomic scale. In this infinitely small world, the rules change. A particle can exist in multiple states simultaneously—it can be both here and there, on and off at the same time. It is this baffling principle that underpins the promise of quantum computers: machines capable of solving certain complex problems at a speed that no classical computer will ever be able to match.
But building a quantum computer first requires knowing how to manipulate its basic building blocks: qubits. Whereas a classical bit can be either 0 or 1, a qubit can be both at the same time. To achieve this, physicists use a fundamental property of particles called spin—a kind of internal orientation, like a microscopic compass. These spin qubits must be operated at temperatures close to absolute zero—about -273°C—to remain in their fragile quantum state. Even the slightest increase in temperature, as little as one-thousandth of a degree, is enough to disrupt everything.
Instead of just putting up with this heat, can't we also make the most of it?
This is the two-part question that Boris Brun-Barrière has been tackling since his arrival at theUniversité Grenoble Alpes in December 2023. By combining expertise in solid-state physics, theoretical simulations, and quantum device engineering, he seeks to understand—and control—thermal effects in the most promising quantum systems.
Understanding how heat affects qubits means tackling one of the most tangible obstacles on the path to quantum computers.
Spin qubits are among the most promising candidates for building the quantum processors of the future. Made of silicon—the same material as our ordinary microchips—they have the advantage of being extremely miniaturizable and compatible with existing manufacturing techniques. But they are also extraordinarily sensitive to their thermal environment.
When these qubits are manipulated using microwave fields, the immediate environment heats up. This heating, however slight, disrupts the qubits in ways that are not yet fully understood. To observe and measure this, the team developed an ultrafast thermometry technique capable of detecting temperature variations on the order of a millikelvin—that is, one-thousandth of a degree—on timescales of the order of a microsecond (Champain 2024). This is an unprecedented precision tool at these nanometric scales and extreme temperatures.
The next step was to identify the physical origin of these effects. By studying qubits based on “holes”—the oppositely charged counterparts of electrons in silicon—the team was able to show that it is an interaction specific to holes that creates their particular sensitivity to heat (Champain 2025). This is a groundbreaking discovery: it paves the way for qubits capable of withstanding these thermal perturbations by identifying specific magnetic field configurations in which heat sensitivity is almost completely eliminated. At the same time, the team also demonstrated that it is possible to shield these same qubits from parasitic electrical disturbances in their environment—another major source of errors—thereby opening the door to very high-quality spin qubits (Bassi, Nature Physics 2026).
A third challenge has now emerged: the interaction of hole qubits with the surrounding silicon nuclei, which carry nuclear spin. This interaction, which is still poorly understood, is one of the remaining factors limiting the coherence of qubits, and is the subject of ongoing research within the team.
But heat isn’t just a challenge to overcome—it can also be a signal to harness. Alongside his work on qubits, Boris Brun-Barrière is developing a new generation of bolometers—extremely sensitive radiation sensors based on two-dimensional germanium. The principle: dissipating the energy of photons in a tiny absorber, whose temperature is measured in real time. Thanks to their very low heat capacity, these materials form thermal detectors with exceptional sensitivity, in principle opening up the possibility of detecting single microwave photons—a missing piece in the puzzle of quantum technologies.
The results now exceed the state of the art: a decisive turning point for this new field, which has brought together an international consortium around an ambitious European project.
This research is part of what physicists call the “second quantum revolution”: our new ability to isolate, manipulate, and read individual quantum objects. This new paradigm promises sensors with unparalleled sensitivity, extreme miniaturization, and—a goal that is still distant but real—computers capable of solving certain classes of problems much faster than any classical machine.
There is still much to be understood about how quantum systems interact with their environment. It is precisely this tension between the quantum world and the real world—imperfect, noisy, and hot—that this physicist from Grenoble has chosen to place at the center of his work.
Quantum thermodynamics is currently one of the most active fields in fundamental and applied physics. How can we manage energy dissipation as quantum processors become more complex? How can we harness thermal effects rather than simply endure them? What new quantum sensors will the mastery of microwave radiation enable us to build?
Building on close collaborations with the CEA and European partners, and drawing on his role as director of the international Master’s 2 program in “Quantum Information and Quantum Engineering” at UGA, Boris Brun-Barrière is also training the next generation of specialists in emerging quantum technologies—technologies that could profoundly transform our relationship with computation and measurement in the future.
