Colloquium: Frontiers in Materials Science 2025. Serge Reynaud. «Vacuum fluctuations and Casimir forces»

Empty space contains vacuum fluctuations which are responsible for observable physical effects such as Casimir forces felt by any object as a result of radiation pressure of these fluctuations. This prediction of Quantum Field Theory lies at the interface with open problems of modern physics such as the puzzle of vacuum energy.

The ideal expression which was written by Hendrik Casimir for perfect mirrors at zero temperature is not sufficient for comparison with experiments. Optical properties of mirrors, thermal fluctuations, dissipation, geometry, surface defects, have to be taken into account to this aim [1].

Casimir forces are ubiquitous in many domains of physics. It has recently been shown in experiments performed at UFRJ Rio de Janeiro [2] and in theoretical developments that dielectric matter feels the Casimir force in salted water, which can be important down to the cell scale [3].

[1] “Casimir forces”, Lectures at Les Houches Summer School, Quantum Optics and Nanophotonics, Fabre C. ed. (Oxford Univ Press, 2017) 407-455 arXiv.

[2] “Probing the screening of the Casimir interaction with optical tweezers”, Physical Review Research 3: 033037 (2021) doi-arXiv.

[3] “Universal Casimir attraction between filaments at the cell scale”, New Journal of Physics 26: 013009 (2024) doi-arXiv.

Serge Reynaud is full professor at the Laboratoire Kastler Brossel and Collège de France, working on quantum fluctuations (Casimir effect) and relativity (including gravitational waves). He is internationally known for his pioneering contributions in quantum optics together with Claude Cohen-Tannoudji, with whom he introduced the "dressed atom picture". His probability approach, based on the waiting time distribution (which he calls himself the "delay function"), provides powerful techniques to describe the emission. His work with Dalibard on detuned resonance fluorescence also inspired many experiments and theoretical works of prime interest for the community working on quantum physics.