Redefining Genuine Multi-Party Nonlocality for Quantum Networks

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Quantum nonlocality is a fascinating phenomenon. To observe it, one makes simultaneous measurements at two or more locations, potentially separated by a great distance, of tiny quantum particles such as photons that have been previously entangled. These measurements reveal patterns that cannot be explained by any possible local pre-existing properties of the particles – the particles appear to be responding to the measurements in a random, but instantly coordinated, manner. And while quantum nonlocality is reasonably well understood for measurements at two separate locations of two entangled particles, it is less well understood for three or more separated measurements of multiple entangled particles. The work of this project is to better understand quantum nonlocality in this multiple-particle setting – in what ways is it fundamentally different from the two-location variant? In addition to building our understanding of this fascinating phenomenon, this work has significance for quantum communication and cryptography protocols.New operational perspectives on quantum networks have recently contributed to compelling redefinitions of what types of nonlocal effects should be considered genuinely multipartite nonlocal – that is, what types of effects transcend the two-location form of nonlocality in a fundamental manner. This project aims to precisely characterize the patterns of experimental statistics that are consistent with each of these various new definitions of genuine multipartite nonlocality, and to refine interpretations of the phenomena that satisfy one of these definitions but not another. This will lead to a better understanding of potential experiments that could exhibit the various forms of genuine multipartite nonlocality. This new knowledge will be applied to quantum information protocols such as the distribution of secret cryptographic key to multiple parties, analyzing how the new definitions of genuine multi-party nonlocality relate to the secrecy and effectiveness of such tasks.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.