From Single-Protocol to Large-Scale Multi-Protocol Quantum Networks

In the initial stage of the quantum Internet, most of the practical quantum networks have been deployed relying on diverse individual quantum key distribution (QKD) protocols. However, this single-protocol paradigm cannot fulfill the heterogeneous requirements of the users, hence limiting the market penetration of quantum networks. Given the recent advances in QKD protocols, the next generation quantum networks are expected to support both legacy and emerging QKD protocols. However, the evolution from single-protocol to multi-protocol quantum networks poses numerous challenging problems. As a remedy, we conceive a practical protocol translation framework for supporting this migration from single-protocol to large-scale multi-protocol quantum networks. Furthermore, we propose a programmable multi-functional relay node architecture for harmonizing the components of a suitable relay node. A pair<br/>of protocol translation policies are conceived for meeting the challenging security requirements of migration requests, which are compared to the single-protocol-based migration solutions both in terms of the translation success probability attained (i.e., the proportion of migration requests with successful protocol translation) and the average relaying risk probability encountered (i.e., the mean of the relaying risk probabilities of endto-end key negotiation in a quantum network). Finally, we highlight a suite of open problems in both quantum secure direct communication and quantum teleportation for research into future multi-protocol quantum networks.