Research On Several Quantum Secure Communication Methods Based On Non-maximally Entangled Channels

With the advent of the electronic supply era,classical communication faces great challenges in information transmission speed and security.However,due to the characteristics of high communication efficiency,large communication capacity and unconditional security,quantum communication has gradually become a research hotspot in the field of communication.In this thesis,three quantum secure communication schemes are studied with non-maximally entangled quantum state as communication channel.The main contents are as follows:Firstly,a high-dimensional multi-qudit state remote preparation scheme based on butterfly quantum network coding is proposed,which can be used to prepare channels for multi-party quan tum key agreement schemes.Compared with the existing remote state preparation schemes,this scheme makes use of non-maximally entangled quantum states as communication channels,which has relatively good environmental adaptability;the target channel is obtained through channel modulation,which improves the reliability and stability of the scheme.In addition,network coding technology is used to improve information transmission efficiency and network throughput.Secondly,a multi-party quantum key agreement scheme based on non-maximally entangled four-qubit cluster states is put forward.Since the scheme adopts positive operator-valued measurement,all participants should select the subkey of the common position where the measurement is successful in the raw key sequence as the final agreement key.There is no need to perform complex multi-particle joint measurements,thus reducing the requirements for physical equipment.Compared with the existing quantum key agreement schemes,this scheme can not only achieve fair negotiation of shared keys,but also has security performance against attacks,which provides new ideas for studying multi-party quantum key agreement in practical communication scenarios.In the last,a multi-party quantum key agreement scheme based on high-dimensional non-maximally entangled Bell state is proposed.Since the entangled states with more than three qubits are not easy to obtain,the scheme uses high-dimensional two-qubit Bell state as the encoding carrier,which seems more adaptable for physical implementation.Compared with the traditional two-dimensional system,high-dimensional system demonstrates larger information capacity.In addition,the encoding operation adopted in this scheme includes both amplitude and phase parameters where two bits of key information can be negotiated through a single measurement operation,which brings a higher execution efficiency.