Alexandre Baron
Centre de Recherche Paul Pascal, CNRS
Bell’s inequalities and their violation
In 2022, Alain Aspect, John Clauser, and Anton Zeilinger were awarded the Nobel Prize in Physics for “experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.” These experiments provide a fundamental answer to a deeply conceptual question about the nature of reality, particularly concerning locality, hidden variables, and the independence between a physical system and the act of measuring it. It is said to settle a long-standing debate between Einstein and Bohr on the completeness of quantum mechanics.
This presentation aims at explaining Bell’s theorem, how quantum mechanics leads to its violation, and to give an overview of the experimental challenges that had to be overcome to demonstrate this violation convincingly. Rather than a specialist lecture, this will be the perspective of a fellow scientist seeking to make the topic accessible to non-experts, and one who studied at the Institut d’Optique, where Alain Aspect and his collaborators conducted the first loophole-free experiment testing Bell’s inequalities. I also had the opportunity to redo this experiment during a laboratory course there, which deeply influenced my understanding and appreciation of the subject.
