Claude Weisbuch receives the French Academy of Sciences' medal for scientific applications

Academic world, industrial world, start-up world, administrative world, Claude Weisbuch has explored the world of research from many points of view over the course of his career. A graduate of the Ecole Normale Supérieure, he specialized in semiconductor physics, completing his thesis at the Ecole Polytechnique's Laboratory of Condensed Matter for Physics (PMC*) in the late 1960s. The microelectronics revolution made possible by semiconductor materials (the basis of today's transistors) was still in its infancy. “Back then, integrated circuits contained a maximum of twenty transistors; today, processors can contain twenty billion. The evolution has been staggering”, says the physicist. At the time, he was working on fundamental aspects of spin - an intrinsic property of electrons - in semiconductors. Using optical methods, he discovered some of the parameters governing these materials.

From 1979 to 1981, Claude Weisbuch moved to the USA, to Bell Laboratories, famous for the development of communications technologies, but which also had a research division. “I was judged on the fundamental nature of what I was doing, not on its potential for application,” he recalls. Back in France, he managed laboratories at Saint-Gobain and then Thomson-CSF (now Thalès).

There, he and his colleagues discovered the design rules for semiconductor quantum-well lasers. These feature an active region of extremely thin semiconductor layers in which electrons follow the laws of quantum physics. These quantum wells serve as light emission zones for the lasers, particularly in the near infrared, a wavelength band of prime importance for optical telecommunications. This work will have repercussions: “industrialists work by trial and error and, little by little, their designs for semiconductor lasers for telecommunications have converged towards what we had predicted”.

After a stay in Japan, where he first described the fundamental phenomenon of strong coupling between light and matter in solids, Claude Weisbuch decided on a new career path in the early 1990s, at the Direction de la Recherche et de la Technologie (DRET), under the management of the French Ministry of Defense. The aim was to prepare for the future, particularly of defense systems. “My job was to assess the quality and relevance of the research carried out in all areas, including gunpowder, jet engines, shielding, electronic components and so on. And I also managed a small budget for basic research. This is how, for example, we were able to fund research into cold atom mirrors. “20 years later, there's a French start-up marketing gravitational constant measurement systems based on cold atoms”, adds the physicist, underlining the importance of supporting long-term research with no immediate applications.

Following this experience in the world of administration, Claude Weisbuch returned to research, still at the PMC but also at the University of California, Santa Barbara, where he was appointed professor. He became interested in light-emitting devices, in particular LEDs, also made from semiconductor materials. They are now widely used in lighting, for example. The aim was to increase the fraction of light leaving the active layer where it is produced. Thanks to this expertise, in 2001 he co-founded Genewave, a start-up dedicated to molecular diagnostics. This involved manufacturing biochips capable of detecting sequences of DNA or RNA strands, to identify viral strains for example, using the light emitted by fluorescent molecules attached to these strands. The adventure lasted 20 years, before the business was bought by an American group in 2021. “On the one hand, I regret not having succeeded in setting up a major company in France, but on the other, I'm satisfied, because I've had opportunities, trained people and provided further proof that physics can be useful,” confides Claude Weisbuch, who is continuing his exploration of the fundamental properties of LEDs, convinced that there are still important things to discover.

Congratulations also to Sébastien Galtier, researcher at the Plasma Physics Laboratory (LPP*), who received the Cécile DeWitt-Morette/École de physique des Houches/CFM Fondation pour la recherche prize.

*PMC: a joint research unit CNRS, École Polytechnique - Institut Polytechnique de Paris, 91120 Palaiseau, France

*LPP: a joint research unit CNRS, Observatoire de Paris-PSL, Sorbonne Université, Université Paris-Saclay, École Polytechnique - Institut Polytechnique de Paris, 91120 Palaiseau, France