Nonlocality in quantum physics and beyond

Nicolas.Brunner

University of Geneva

Abstract

The principle of locality—the fact that an object is influenced directly only by its immediate surroundings, and not by remotely located objects—is a central to classical physics. The fact that quantum mechanics is at odds with the principle of locality is one of the most distinctive and counterintuitive aspects of the theory. In fact, quantum nonlocality is nowadays often viewed as the theory’s defining feature. In recent years, tremendous progress has been achieved in the research field.
In particular, it was realized that there exists various inequivalent forms of non-locality in quantum mechanics, namely entanglement, EPR steering, and Bell non-locality. Moreover, it was discovered that the notion of Bell non-locality can be studied in its own right, without any reference to quantum mechanics. This model-independent approach to nonlocality has already significantly deepened our understanding of the foundations of quantum mechanics. Finally, these ideas also lead to ’device-independent’ quantum information processing. This represents a new paradigm for quantum information processing, the goal of which is to achieve an information-theoretic task (such as cryptography or certified randomness generation) and guarantee its security without relying on any assumptions about the functioning of the devices used in the protocol. Beyond the conceptual interest, this approach offers interesting perspectives for practical implementations. Being device-independent, such protocols are more resistant to device imperfections compared to standard protocols.

After introducing the main concepts of quantum non-locality, this tutorial talk will review recent progress in this area.