Research On The System Of Continuous Variables Quantum Communication With Entanglement

Quantum communication can be divided into continuous variables quantum communication(CV-QC)and discrete variables quantum communication(DV-QC)according to the character of transmitted information.The former has some advantages,such as huge information capacity,strong signal and flexible modulation and easy realization,etc..The latter has some shortcomings including small capacity,weak signals,hard-realized single-photon source,susceptible to interference and attenuation.Therefore more and more people pay attention to CV-QC.Quantum neural network(QNN)is a new type of neural model which is composed by the principle of quantum computing and artificial neural network(ANN),it can be modeled by quantum circuit.QNN uses the performance of quantum parallel computing and quantum entanglement states to overcome the shortcomings of ANN,such as small information capacity,slow network processing and long training time and so on.There are several DV-QNN models proposed,such as qubit neural model,entangled neural network and multi-universe model,etc..However,the models are applied to the DV quantum information.With the development of CV-QC,it is necessary to setup a QNN model with continuous variables.Unfortunately,there is little research on this field.In this thesis,we setup a coherent states quantum neural network(CS-QNN)model,and using CS-QNN to assist CV-QC.The main aspects are as follows.Firstly,the background of this research is introduced,the research status of continuous variable quantum communication is discussed,then research results at home and abroad are summarized.And the research contents and innovations of this subject are described briefly.Secondly,the basic principles of QNN are introduced,including quantum logic gate,quantum circuit,entangled neural network and QNN model based on quantum circuit.After that,some CV quantum gate based on coherent states are expressed,such as phase rotation gate,Hadamard gate and double-bit CNOT gate.Aside that,we put forward a optical setup of CV quantum AND gate based on coherent states,and analyze the successful probability of optics setup.The optical setup is made up of some linear optical devices like light splitters(BS),phase shifters(PS)and photon counters.Then we construct a coherent states multi-bit controlled not gate combining coherent states AND gate and double-bit CNOT gate,which laid the foundation for the proposed CS-QNN model.Finally,a model of CV-QNN based on coherent states multi-bit CNOT gate is proposed.This model is represented by quantum circuit.In order to verify the feasibility and effectiveness of this model,we introduce it into the continuous variables quantum teleportation(CV-QT)system which under the amplitude damping channel.The purpose is to realize the recovery of the signal affected by noise.In CS-QNN,only 10%signals are extracted into trainer for the communication quality considering of CV-QT.The simulation results show that the fidelity of the output signal of CV-QT with CS-QNN auxiliary significantly increased to approach 1.Compared with the scheme based on entanglement recompensation and matching compensation mechanism,the scheme we proposed can ensure the quality of communication.