The Violation of Bell-CHSH Inequalities Leads to Different Conclusions Depending on the Description Used

Since the experimental observation of the violation of the Bell-CHSH inequalities, much has been said about the non-local and contextual character of the underlying system. However, the hypothesis from which Bell’s inequalities are derived differ according to the probability space used to write them. The violation of Bell’s inequalities can, alternatively, be explained by assuming that the hidden variables do not exist at all, that they exist but their values cannot be simultaneously assigned, that the values can be assigned but joint probabilities cannot be properly defined, or that averages taken in different contexts cannot be combined. All of the above are valid options, selected by different communities to provide support to their particular research program.

Lecture 12- Entanglement

We will discuss the creation of entangled photons and how they can be used for the test of Bell’s inequalities.

Hanbury Brown and Twiss, Hong Ou and Mandel effects and other landmarks in quantum optics: from photons to atoms

The second quantum revolution is based on the concept of entanglement and the ability to observe and manipulate individual quantum objects. This notion was prompted by celebrated quantum optics landmark experiments. The author’s group has endeavored to revisit these experiments with atoms instead of photons, more precisely metastable helium atoms (He*), which can be detected one by one, as photons. The first landmark that announced the beginning of modern quantum optics was the Hanbury Brown and Twiss effect: it has been studied not only with 4He* atoms, which are bosons, but also with 3He* atoms, which are fermions. The group has then observed the atomic Hong Ou and Mandel effect, and, more recently, shown the possibility to use a slightly generalized scheme to test Bell’s inequalities with atoms entangled in momentum.