QRC Seminar Series - Prof. Rafael Chaves

Title:

Interventions, causality and quantum correlations

Abstract:

Since Bell's theorem, it is known that the concept of local realism fails to explain quantum phenomena. Indeed, the violation of a Bell inequality has become a synonym of the incompatibility of quantum theory with our classical notion of cause and effect. As recently discovered, however, the instrumental scenario -a tool of central importance in causal inference- allows for signatures of nonclassicality that do not hinge on this paradigm. If, instead of relying on observational data only, we can also intervene in our experimental setup, quantum correlations can violate
classical bounds on the causal influence even in scenarios where no violation of a Bell inequality is ever possible. That is, through interventions, we can witness the quantum behaviour of a system that would look classical otherwise. In this talk we will see how the role of instrumental variables in causal inference has to be revisited in the presence of quantum common causes, present a photonic experiment implementing this new and stronger form of nonclassicality and discuss its use in cryptographic protocols.