Study On Characteristics Of Underwater Quantum Communication

Underwater quantum communication can carry quantum state information through photons.Compared with traditional underwater electromagnetic wave communication and acoustic communication,the underwater quantum communication has the advantages of high safety,fast communication rate and large information capacity.It is a new underwater communication mode for the future.However,the seawater is a complex mixture,when the optical quantum signal is transmitted underwater,it will be disturbed by the absorptio n,scattering and turbulence effects of seawater,resulting in the decline of the transmission performance of underwater quantum communication,the increase of bit error rate and the change of channel capacity.Therefore,the characteristics of underwater quantum communication are studied in this paper.The main research contents are as follows:Firstly,the vertical underwater quantum transport characteristics under the influence of chlorophyll concentration are studied by using the Monte Carlo method.In the research,the vertical transmission model of underwater quantum channel based on polarized photons is established,and four typical sea areas with different attenuation are divided according to the chlorophyll concentration on the surface of seawater.On this basis,the variation laws of chlorophyll concentration,absorption coefficient and scattering coefficient of seawater with the seawater ’s depth are analyzed.Then,the scattering,attenuation and polarization characteristics of polarized photons in the four sea areas are simulated and analyzed by using the Monte Carlo method.Moreover,the formulas for calculating the total number of photons received at different transmission distances are given.Secondly,the influence of weak ocean turbulence on the characteristics of underwater quantum communication is studied.In the research process,an ocean turbulence power spectrum in unstable stratified seawater is modified with reference to the outer scale form of Greenwood.Based on the modified ocean power spectrum,the beam drift and light intensity scintillation model under weak ocean turbulence are deduced.The effects of beam propagation distance,turbulent dissipation rate per unit mass of ocean,mean square temperature dissipation rate and effects of external scales of turbulence and temperature salt balance parameters on beam drift and intensity sci ntillation are also investigated.Furthermore,the influence of several important ocean characteristic parameters on the channel capacity of seawater qubit flip channel under weak ocean turbulence is analyzed.Finally,in order to further study the perform ance of underwater quantum communication system,combined with the absorption,scattering and turbulence effects of seawater on optical signal,the variation law of quantum bit error rate of polarized light signal with seawater depth in seawater channel in weak turbulence area of four typical sea areas is simulated and analyzed.