Multipartite secret key distillation and bound entanglement

TL;DR

This paper extends quantum cryptography protocols beyond pure entanglement to multipartite states, introducing new bound entangled states with cryptographic key and estimating key rates.

Contribution

It generalizes the cryptographic paradigm to multipartite states and constructs new classes of bound entangled states with cryptographic key.

Findings

Constructed multipartite bound entangled states with twisted GHZ structure

Quantitatively estimated cryptographic key lower bounds

Extended the cryptographic paradigm to multipartite scenarios

Abstract

Recently it has been shown that quantum cryptography beyond pure entanglement distillation is possible and a paradigm for the associated protocols has been established. Here we systematically generalize the whole paradigm to the multipartite scenario. We provide constructions of new classes of multipartite bound entangled states, i.e., those with underlying twisted GHZ structure and nonzero distillable cryptographic key. We quantitatively estimate the key from below with help of the privacy squeezing technique.