Experimental tests of local realism and the birth of quantum technology
Morgan Mitchell, ICFO
"Aula Magna Enric Casassas", Physics Faculty
Abstract: The 2022 Nobel Prize in Physics was awarded to Alain Aspect, John Clauser and Anton Zeilinger for Bell tests, experiments to observe non-local correlations that contradict the commonsense world-view described by Einstein, Podolsky and Rosen in their famous 1935 article. Since 1972, Bell tests have shown, with ever-increasing sophistication, that the bizarre features of quantum theory exist not only on paper, but also in the physical world. In this talk I will briefly review the “debate" between Einstein and Bohr that gave rise to the EPR argument, Bell’s formalization of Einstein’s intuitions, and the structure and requirements of a Bell test. Unlike most other physics experiments, Bell tests aim to disprove a broad class of models defined by a physical property (locality) and a metaphysical property (realism). Because of this extraordinary ambition, experimental work on this topic presents methodological challenges rarely encountered in other areas of science. I will discuss how three generations of experiments, represented by Clauser in the 1970s, Aspect in the 1980s, and Zeilinger since then, have progressively refined Bell tests and our understanding of them. The story involves a lot of new technology for generating and detecting entangled particles, the discovery of new “loopholes” and methods to “close” them, and crazy-sounding proposals that led to practical quantum technologies.