Alain Aspect: From Einstein doubt to quantum bit: A second quantum revolution

In 1935, with co-authors Podolsky and Rosen, Einstein discovered a weird quantum situation, in which particles in a pair are so strongly correlated that Schrödinger called them "entangled". By analyzing that situation, Einstein concluded that the quantum formalism is incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics.

In 1964, John Bell discovered that it is possible to settle the debate experimentally, by testing the now celebrated "Bell's inequalities", and to show directly that the revolutionary concept of entanglement is indeed a reality. A long series of experiments, started in 1972, yield more and more precise results, in situations closer and closer to the ideal theoretical scheme.

After explaining the debate, and describing some experiments, Alain Aspect also shows how this conceptual discussion has prompted the emergence of the new fields of quantum information and quantum technologies.

Alain Aspect is an alumnus of the École Normal Supériere (ENS) in Cachan and the Université d'Orsay. He has held positions at the Institut d'Optique, the ENS in Yaoundé (Cameroon), ENS in Cachan, ENS/Collège de France, and CNRS.

He is currently a professor both at the Institut d'Optique Graduate School, where he holds the Augustin Fresnel chair, and at École Polytechnique, in Palaiseau. He is a member of science academies in France, the USA, Austria, Belgium, and the UK. He is the recipient of the CNRS Gold medal, the Wolf Prize in Physics, the Balzan prize on quantum information, the Niels Bohr Gold medal, the Albert Einstein medal, the Ives medal of the OSA and other awards.

His research has focused on tests of Bell's inequalities with entangled photons, wave-particle duality for single photons, laser cooling of atoms with lasers below the one-photon recoil, quantum simulation, and quantum atom optics with ultracold atoms.