Submitted to “Quantum Nonlocality and Reality – 50 Years of Bell’s theorem”
1964 was a wonderful year for physics, in this “annus mirabilis”, summarising and simplifying a little, quark model was proposed by Gell-Mann and Zweig and charm and colour properties were introduced, Higgs published his work on the scalar boson, $\Omega$ boson and CP violation were discovered, cosmic background radiation was identified and, finally, Bell inequalities were suggested.
Most of these works were later subjects of a Nobel prize. Unluckily John Bell left us too early for this achievement, but, at least in my opinion, his work is probably the most fruitful among all these huge progresses, since now we can recognise that it was the root of a fundamental change in our vision of the physical world, providing, on the one hand, the possibility of a test of quantum mechanics against a whole class of theories (substantially all the theories that we could define as “classical”) and, on the other hand, introducing a clear notion of quantum non-locality, that represents not only a challenge in understanding quantum mechanics, but also one of the most important resources paving the way to quantum technologies that were developed in the last decades based on the quantum correlations discussed in Bell paper.
In the following we will present the experimental progresses in testing Bell inequalities. Rather amazingly even 50 years after Bell’s paper, still a conclusive test of his proposal is missing.
Nevertheless, huge progresses have been achieved respect to the first experiments. We will discuss in detail these developments and the remaining problems for a conclusive test of Bell inequalities.