Last Friday we started +Talks, a series of events in which we invite interesting people to visit us and share their ideas about science, art, technology, and design. Our first guest was Professor Antonio Acín, from the Institute for Photonic Sciences (Barcelona). It was an honor to have Toni, not only because he is a personal friend, but because he is one of the best known experts in quantum science and technologies.
Toni began his presentation by talking about the difficulty in explaining quantum physics to the general public, because of its counter-intuitive results, and our lack of language to talk about phenomena that we don't experience in everyday life. Then he moved on to what, according to him, is the most interesting aspect of quantum physics: the fact that it defies our most basic ideas of logic. He showed us the following inequality A(C+D)+B(C-D)≤2, valid whenever the variables A, B, C, and D can take the values +1 or -1. Just try all possible values for these variables and you will quickly convince yourself that the inequality is correct. What is surprising about this? It turns out that using quantum variables we can get results for the variables that violate this inequality (i.e., that make A(C+D)+B(C-D)>2).
According to Toni, what is perhaps even more important is that this result implies that we cannot assume predetermined values for the quantum variables. We can only say that they really have a value after we measure them. And this is behind several applications in quantum technologies, such as quantum random generators and quantum cryptography.