Theoretical Study On Non-classical Correlation And Quantum Channel Capacity Characteristics In Turbulent Channels

The 21 st century is the information age.In the face of high-density information storage,high-efficiency computing and information security,the classical information field is faced with great challenges.At this time,the development of quantum information technology becomes particularly important.When a series of difficult problems appear in the field of classical communication,quantum information technology can propose corresponding solutions.The development of quantum computing,quantum teleportation,quantum key distribution and other technologies can effectively guarantee the security of information transmission.At the same time,the superposition property of quantum state can encode and store quantum information of higher density,and the coherent property of quantum state can make the multi-volume subsystem in the quantum entanglement state.Quantum entanglement can be applied to many information processing problems and is regarded as a very important resource in the field of quantum information science.In recent years,people begin to pay attention to the underwater wireless optical communication(UWOC)system,hoping to find the conditions and methods that are conducive to beam transmission in the water.In the process of quantum information theory research,quantum channel capacity and quantum entanglement,as the basic quantum information resources,will inevitably be affected by the cross-talk of ocean turbulence in the long distance underwater transmission,resulting in the phenomenon of decoherence.Therefore,studying the evolution process of quantum information transmission in ocean turbulence and obtaining the transmission attenuation characteristics of quantum information resources under different conditions of ocean turbulence are of great significance to the research and application of quantum information resources in both theoretical and practical fields.In this paper,we investigate the non-classical correlation and quantum channel capacity properties of orbital angular momentum(OAM)in turbulent ocean channels.The main work contents are as follows:(1)A single photon characteristic system of OAM in ocean turbulence is established,and the channel capacity and track distance are obtained by using Laguerre-Gaussian beam for theoretical calculation and simulation.It is found that the channel capacity decreases with the increase of the propagation distance,the mean square temperature dissipation rate of the fluid,the contribution ratio of temperature to salinity,and the decrease of the initial OAM quantum number,the kinetic energy dissipation rate per unit mass of the fluid and the internal scale factor.In contrast,although the change rule of track distance is opposite to the channel capacity,the physical meaning it represents is consistent,which provides another research direction for underwater wireless optical communication.(2)A two-photon characteristic system of OAM in ocean turbulence was established,and the quantum entanglement and quantum coherence changes in vortex beam propagation were investigated by using the Laguerre-Gaussian beam.The results show that increasing the transmission distance and equivalent temperature structure parameters,and decreasing the purity factor and azimuth quantum number will decrease the transmission quality of quantum information resources.Because quantum entanglement will suddenly disappear after a certain transmission distance,resulting in the phenomenon of sudden death of entanglement,and quantum coherence only shows the characteristics of asymptotic attenuation,will not disappear to zero,so it can better show the quantum distribution.Finally,an interesting observation was made that there is an optimal beam width almost independent of wavelength that maximizes the quantum resources.(3)Using quantum information resources such as quantum channel capacity and quantum trace distance,the propagation law of Bessel-Gaussian beam in underwater wireless optical communication is discussed.After simulation,it is found that the shorter the propagation distance,the higher the dissipation rate of kinetic energy per unit mass,the lower the mean square temperature dissipation rate and the smaller the temperature-salinity contribution ratio,the better the communication quality of the quantum channel.Similar to classical channel capacity studies,quantum channel capacity is also sensitive to the changes of internal scale factors and anisotropic factors.Compared with less OAM modes,more OAM modes enhance the quantum channel capacity of FBG and reduce the attenuation of quantum trace distance.In addition,Bessel-Gaussian beams have better anti-turbulence stability than Laguerre-Gaussian beams in underwater wireless optical communication.The results show that the attenuation of quantum channel capacity can be reduced by allocating quantum superposition states.These results provide theoretical references for the design of quantum communication systems in real free space.