Alain Aspect: The physicist who made entanglement an experimental reality

For Einstein and other physicists of his generation, the strongly counter-intuitive features of quantum mechanics were very hard to accept, given that our intuition is based on the classical world around us. This EPJ D Topical Issue examines the discoveries, motivations, and continuing legacy of Alain Aspect: the physicist whose experiments, along with those of John Clauser and Anton Zeilinger, have made that quantum entanglement, an essentially non-classical feature, is now also an experimental reality, exploited in science and technology.

New York | Heidelberg, 24 January 2023

In 1935, a trio of physicists, Albert Einstein, Boris Podolsky, and Nathan Rosen, introduced an argument concluding to the “incompleteness” of quantum mechanics. Their ideas stimulated a major work in 1964 by John Bell, who was able to turn a somehow philosophical discussion into mathematical inequalities, and from there into possible experiments.

In January 2023, EPJ D presents a Topical Issue in honour of Alain Aspect: the physicist who put Bell’s inequalities under particularly stringent test, through a set of ground-breaking experiments at the beginning of the 1980s. This Topical Issue is particularly well timed, since Alain Aspect, along with John Clauser and Anton Zeilinger, have received the 2022 Nobel Prize in Physics on 10 December 2022, in recognition of their major contributions to the understanding of the world around us.

After the initial publication of Bell’s inequalities in 1964, it took some time to give them a form allowing a first experimental test. This was first achieved by John Clauser in 1972, followed by several other experiments. The next major step was achieved by Alain Aspect in his doctoral thesis, completed in 1983, and saw his results confirmed in more and more refined experiments. In particular, several results obtained by Anton Zeilinger and his team established definitively that observations are in full agreement with quantum mechanics, and violate Bell’s inequalities – and thus, the “local realistic” worldview attached to them.

This Topical Issue was initially designed to honour Alain Aspect’s achievements on the occasion of his 75th birthday, and it could hardly be more timely. It provides a set of personal and historical perspectives on Alain’s career. It also presents a series of scientific articles providing fascinating perspectives for quantum technology and information science, whose principles are founded on quantum entanglement, as evidenced in Aspect’s experiments.

Together, the papers in this EPJ D Topical Issue highlight the story and continuing legacy of a bold, friendly, and enthusiastic physicist, who was never deterred from questioning the deepest issues posed by nature to the wider physics community.

Reference: Clément, D., Grangier, P. & Thywissen, J.H. Quantum optics of light and matter: honouring Alain Aspect. Eur. Phys. J. D 77, 2 (2023). https://doi.org/10.1140/epjd/s10053-022-00578-1