It isn’t often that a PhD supervisor asks a student to look into a research concept that Einstein had originally dismissed, but that is how Alain Aspect became involved in quantum mechanical entanglement. The roots of the Nobel Prize in Physics in 2022, awarded to Aspect, John Clauser and Anton Zeilinger, go back to the Gedankenexperiments or thought experiments of the Einstein-Podolsky-Rosen (EPR) “paradox” paper in 1935. The paper described the phenomenon of two particles entangled in an abstract space, which influence one another despite being separated.
In his Nobel Lecture, Aspect explains that if we follow Einstein's world-view, we can describe this correlation as comparable to two organisms with the same chromosome. Nearly thirty years after the EPR paper was published, the physicist John Stewart Bell showed that if the comparison holds, the correlation between measurements of the particles will be constrained. However, the correlations between particles will be stronger, according to quantum mechanics, if the particles are entangled. If the experiment agrees with the quantum mechanical predictions, the local realist world view of Einstein will be proven unable to describe the situation.
In 1981, at Institut d'Optique d'Orsay (now with Université Paris-Saclay) Aspect set out to test Bell’s theorem and investigate the interaction of particles in entangled states. Using an experimental set-up with a krypton laser, calcium atoms, two-channel polarizers, and polarization beam splitters determined the quantum mechanical behaviour of two photons in a 12-metre tube, violating Bell’s inequalities. The series of experiments yielded results in agreement with quantum mechanics, forcing us to abandon the local realist world view. They abolished the idea that quantum mechanics is a theoretical curiosity and set the stage for the onset of quantum technology based on entanglement.
Alain Aspect was born on 15 June 1947 in Agen, France. He studied physics at the École Normale Supérieure de Cachan (now ENS Paris-Saclay) and at the Université d’Orsay, where he also took his Master’s degree. Between 1971 and 1974, Aspect volunteered as a teacher in Cameroon. Back to France, he worked as a lecturer at the ENS de Cachan and as a researcher at Institut d'Optique where he completed his PhD in 1983 which was titled “Three Experimental Tests of Bell’s Inequalities With Entangled Photons.” After receiving the Servan Prize from the French Académie des Sciences, Aspect became a senior scientist at the Collège de France, where he worked with Claude Cohen-Tannoudji (Nobel Laureate 1997) on laser cooling of atoms. In 1992, he was appointed a CNRS senior scientist at the Laboratoire Charles Fabry de l’Institut d’Optique, where he started a research group on atom optics. He was also appointed a professor at the Institut d'Optique and at the École Polytechnique. Alain Aspect is married and has two children and seven grand-children.
