Fundamental limitation on quantum broadcast networks

The ability to distribute entanglement over complex quantum networks is an important step towards a quantum Internet. Recently, there has been significant theoretical effort by mainly focusing on the distribution of bipartite entanglement via a simple quantum network composed only of bipartite quantum channels. There are, however, a number of quantum information processing protocols based on multipartite entanglement, rather than bipartite one, which should be served more naturally by a quantum broadcast network, rather than such a simple network. In this work, we present a general framework for deriving upper bounds on the rates at which GHZ states or multipartite private states can be distributed among a number of different parties over any quantum broadcast network. We also discuss how lower bounds can be obtained by combining generalisation of an aggregated quantum repeater protocol with graph theoretic concepts.