Alain Aspect (born June 15, 1947) is a French physicist who performed the crucial "Bell test experiments" that showed that Albert Einstein, Boris Podolsky and Nathan Rosen's "spooky action at a distance", did in fact appear to be realised when two particles were separated by an arbitrarily large distance. A correlation between their wave functions remained, as they were once part of the same wave-function that was not disturbed before one of the child particles was measured.
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- La principale difficulté pour vulgariser la physique quantique, c'est qu'on ne sait pas très bien comment en fabriquer des images dans notre monde. C'est en ce sens qu'elle est vraiment contre-intuitive.
"Introduction: John Bell and the second quantum revolution" (2004)
"Introduction: John Bell and the second quantum revolution", in J. S. Bell, Speakable and Unspeakable in Quantum Mechanics (2nd ed, 2004)
- The most remarkable feature of Bell's work was undoubtedly the possibility it offered to determine experimentally whether or not Einstein's ideas could be kept. The experimental tests of Bell inequalities gave an unambiguous answer: entanglement cannot be understood as usual correlations, whose interpretation relies on the existence of common properties, originating in a common preparation, and remaining attached to each individual object after separation, as components of their physical reality.
- I think it is not an exaggeration to say that the realization of the importance of entanglement and the clarification of the quantum description of single objects have been at the root of a second quantum revolution, and that John Bell was its prophet. And it may well be that this once purely intellectual pursuit will also lead to a new technological revolution.
- Certainly we do not need quantum mechanics for macroscopic objects, which are well described by classical physics – this is the reason why quantum mechanics seems so foreign to our everyday existence.
- As a witness of that period, I am also deeply convinced that John Bell indirectly played a crucial role in the progress of the application of quantum mechanics to individual objects, microscopic and mesoscopic. The example of his intellectual freedom, that had led to the recognition of the importance of entanglement, was no doubt an encouragement to those who were contemplating the possibility of developing new approaches, beyond the so-efficient paradigm developed decades earlier. His example opened the gate for new quantum explorations.
- John Bell devoted most of his efforts to conceptual and theoretical questions. Would he have liked that I also stress the importance of the technological revolutions that were, and will be, enabled by the conceptual revolutions? I cannot tell, but we know that he started his career in accelerator design, and that he always showed a profound respect for technological achievements. I like to think that he would have loved quantum-jumps-based atomic clocks, as well as entangled qubits.