| Quantum communication has been researching and developing for more than thirty years,quantum secure communication based on quantum key distribution has gradually entered the practical stage.Quantum communication using fiber channel as transmission medium have realized quantum secure communication experiments whose transmission distance over thousands of kilometers with the help of trusted relay,at the same time,the satellite platform-based experiments also be realized,which achieve the verification of quantum secure communication between continents.Compared to fibre channel,free-space always is a popular research topic because its flexibility.In addition to QKD based quantum secure communication,quantum illumination with the help of quantum entangled states can also be used for quantum communication,which has unique advantages in terms of security and it also can resist noise better.At the same time,the THz frequency band has also attracted the attention of researchers,because it has better performance on penetrating objects,catch and track target objects more easily.The paper studies quantum communication technology based on quantum illumination in the near infrared bands and THz bands.First of all,the paper introduce development and research of quantum communication based on fibre channel and free-space carefully.The influencing factors of free space channel are analyzed,and the advantages of quantum illumination technology and terahertz band communication are introduced.Secondly,we introduced the basic knowledge about quantum secure communication—two principles of quantum mechanics and related knowledge of information theory,the atmosphere and turbulence that have the greatest impact on free space.Then the basic principles and related basic knowledge of quantum illumination technology,which is the core of this article,and the key technologies and advantages of terahertz band are elaborated,that lay the foundation for the research of the paper.Thirdly,as the greatest factors in free space quantum secure communication,including the absorption of water and carbon dioxide in the atmosphere,the scattering of aerosol particles,and natural weather conditions are discussed.At the same time,the atmospheric turbulence is separated from other atmospheric impact factors,studies separately and propose another way to estimate turbulence effects.The transmission loss due to turbulence is estimated by the ratio of the Gaussian intensity of the spot that reaches the receiver under different turbulence conditions.On the basis of the above,an improved downlink transmission model is established,and the link transmission rate is analyzed.After determining the influence of the transmission channel,the composition and working process of the free space communication system based on the principle of quantum illumination are given,and obtain the error probability of Alice and Eve in this case.The results show that Alice's error probability is less than5.1?10-7,while the eavesdropper Eve's error probability exceeds 28%,which fully reflects the security advantages of the quantum lighting system,which fully reflects the security advantages of the quantum lighting system.Fourthly,based on the near infrared communication in Chapter 3,we expanded the laser source to THz.Using different frequency to obtain the terahertz source first,and generate the entangled terahertz photon pairs.Alice keeps one photon locally,sends another photon to Bob,and delays the transmission of local photons through the delay line.After modulation,Bob returns the signal to Alice through the same channel.The eavesdropper present in the channel sends its own signal back to the sender along with the returned signal and the generated noise.Finally,Alice separates the signals through multiple CWDMs and performs joint measurement with the local signals.Based on the measurement results,the system performance parameters are further calculated and the system security is analyzed.Finally,we summarize the research content of this article,and prospect the following further improvements. |
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