Multi-user quantum network system and quantum communication using χ-type entangled states

Abstract

A multi-user quantum direct communication network system for N users utilizing χ-type entangled states is proposed. The network system is composed of a communication center, N users, and N quantum lines linking the center and the N users. There is no quantum line among users; therefore, only N quantum lines are necessary for the communication between users. Using one χ-type entangled state, in this protocol, we are able to send two bits of information through direct communication and, at the same time, share two bits of quantum keys. The security of the protocol will be analyzed.