3 December 2025

9:50 AM – 10:35 AM

Amphi Grand Kursaal

Gautier Depambour

A former student of École CentraleSupélec, Gautier Depambour is currently a postdoctoral researcher in the history of physics at Paris Cité University, at the SPHere (Sociology, Philosophy, History of Science) and MPQ (Materials and Quantum Phenomena) laboratories. His research focuses on the history of quantum optics from the 1950s to the 1980s, to which he devoted his thesis, as well as on the role of Bell’s inequalities and quantum entanglement in the development of quantum technologies since the 1980s. He has also published the book Idées de génies with Etienne Klein (Flammarion, 2021) and collaborated with Alain Aspect on the book Si Einstein avait su (Odile Jacob, 2025).

How was quantum entanglement demonstrated experimentally?

Quantum entanglement, which reflects a mysterious connection between particles separated in space, is certainly one of the strangest phenomena predicted by quantum mechanics. Would you believe it? Its experimental demonstration in the 1970s and 1980s is linked to an extremely simple limit: the number 2! Indeed, as some theorists showed in the 1960s, it is possible to imagine experiments that test an inequality, S ≤ 2 (the simplest form of the famous “Bell’s inequalities”), the violation of which would be a sign of the existence of quantum entanglement. In other words, if precise measurements lead to conclude that a certain experimental quantity S (related to correlations between photons) is strictly greater than 2, then quantum entanglement is not just a whim of eccentric theorists. In this presentation, I will review the history of the foundations of quantum mechanics from the seminal article by Albert Einstein, Boris Podolsky, and Nathan Rosen published in 1935 to the experiments of Alain Aspect and his collaborators in Orsay in the 1980s. I will show that the debate between Einstein and Niels Bohr on the interpretation of quantum mechanics, initially purely philosophical, was projected into the experimental domain thanks to the successive works of David Bohm, John Bell, John Clauser, Michael Horne, Abner Shimony, and Richard Holt. I will then explain how subsequent experiments showed that, under certain conditions, Bell’s inequalities can be violated, which marks a turning point in the history of quantum mechanics.