Research On Multi-party Quantum Simultaneous Dense Coding

Quantum entanglement not only improves computing speed,but also theoretically achieves unconditionally secure information transmission.Compared to classical information transmission,quantum dense coding implemented through quantum entanglement has the ability to transmit two classical bits with only one quantum bit.Due to its strong information transmission capability and large channel capacity,quantum dense coding has become a hot topic in quantum information researches.This thesis focuses on simultaneous dense coding and controlled simultaneous dense coding,and the research contents are as follows:1.Multi-party simultaneous dense coding based on Bell,GHZ and W entangled states as quantum channels are studied.Firstly,a protocol is proposed with one sender and multiple receivers,using an 9)bit quantum Fourier transform to lock the entangled channel.Secondly,the above-mentioned protocol is extended,proposing a simultaneous dense coding protocol involving multiple senders and multiple receivers.The information transmission rate of both protocols are two bits,which are better than the classical communication rate of one bit.Compared to the original scheme,the protocol solves the issue of participant limitations.In the aspect of security,the protocol’s safety has been verified by analyzing both internal and external attacks.2.Multi-party controlled simultaneous dense coding based on GHZ entangled state as a quantum channel for multiple receivers is studied.Under the supervision of a third-party controller,a controlled simultaneous dense coding scheme is designed for one sender and multiple receivers,ensuring that each receiver can obtain two classical bits of information,thus enhancing the security of the protocol.Without the involvement of the controller,the receivers cannot obtain the correct coding information.Compared to the original scheme,the protocol first elaborates the process of implementation using three receivers,then extended to 9)receivers,solving the problem of allowing more than two receivers to simultaneously receive information from the sender under the permission of the controller.