SAMOP 2021 – scientific programme

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QI: Fachverband Quanteninformation

QI 13: Quantum Information and Foundations II

QI 13.1: Talk

Friday, September 24, 2021, 10:45–11:00, H4

Genuine multipartite entanglement is not a precondition for secure conference key agreement — •Giacomo Carrara, Dagmar Bruß, Hermann Kampermann, and Gláucia Murta — Institut für Theoretische Physik III, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany

Entanglement plays a crucial role in the security of quantum key distribution. A secret key can only be obtained by two parties if there exists a corresponding entanglement-based description of the protocol in which entanglement is witnessed, as shown by Curty et al (2004). Here we investigate the role of entanglement for the generalization of quantum key distribution to the multipartite scenario, namely conference key agreement. In particular, we ask whether the strongest form of multipartite entanglement, namely genuine multipartite entanglement, is necessary to establish a conference key. We show that, surprisingly, a non-zero conference key can be obtained even if the parties share biseparable states in each round of the protocol. Moreover we relate conference key agreement with entanglement witnesses and show that a non-zero conference key can be interpreted as a non-linear entanglement witness that detects a class of states which cannot be detected by usual linear entanglement witnesses.