Abstract

The quantum internet holds promise for accomplishing quantum teleportation and unconditionally secure communication freely between arbitrary clients all over the globe, as well as the simulation of quantum many-body systems. For such a quantum internet protocol, we present a general fundamental upper bound on the obtainable entanglement or secret key in terms of the squashed entanglement of the channel [1]. We also consider its converse problem. In particular, we present a protocol [2] constructible from any given quantum network, which is based on running quantum repeaters in parallel over the network. The optimality of this protocol is associated with fundamental problems such as additivity questions for quantum channels and questions on the existence of a gap between the quantum capacity and the private capacity.

[1] K. Azuma, A. Mizutani, and H.-K. Lo, arXiv:1601.02933. [2] K. Azuma and G. Kato, arXiv:1606.00135.