Entanglement in multipartite systems and in particle physics

Since the 1935-publications of Einstein, Podolsky, Rosen und Schrödinger about “entanglement” the researchers and philosophers tried to understand these puzzling quantum correlations. In 1964 John Bell discovered that one cannot understand these quantum correlations via a common local reason. One may summarize it also as: “The whole is greater than the sum of its parts”. Numerous experiments proved the existence of these quantum correlations in different physical systems and it turned out that they allow for novel applications such as increasing the capacity of information or allow for secure communication (cryptography).

In this project we addressed a simple question whether a state of quantum multipartite systems with arbitrary degrees of freedom or a state in High Energy Physics is entangled or not. In particular we were interested to classify and detect different types of entanglement. The answer is not trivial, indeed it was proven that it is never in general possible to find out whether a state is entangled or not in a finite time. Anyway we found general criteria that if they are violated they answer the question. However, if the criteria are not violated, we do not learn something about the entanglement. Fortunately, it turned out that in many cases they are successfully and, moreover, they are experimentally feasible. Herewith, we opened new possibilities for experimenters to question their distinct physical quantum systems. We guess that having now a tool to detect and classify different types of entanglement, we can go over to step two and find out what these new puzzling properties of quantum systems are worse for.