| Since the 20th century,quantum information as a new subject has been widely concerned.Quantum information technology can provide corresponding solutions to a series of difficult problems in the field of classical information.Quantum teleportation,quantum key distribution and other technologies ensure the security of information transmission.The superposition of quantum states enables high-density information to be encoded and stored.As an important quantum information resource,quantum entanglement has been a hot research topic.However,researches have shown that in the implementation of quantum information tasks,there exist other quantum information resources,such as quantum discord and quantum coherence.On the other hand,wireless optical communication brings much convenience to people s life and work.Therefore,it has a good application prospect to add quantum information resources to wireless optical communication.It has been found that if an optical beam has a vortex phase structure,it will have an orbital angular momentum(OAM)mode in the form of integer,which can be well used to encode quantum information in wireless-optical-communication missions.However,due to the fragility of quantum information resources,it is inevitable to be disturbed by the surrounding environment when propagating in free space.During the propagation of light beam,the most common random medium is atmospheric turbulence caused by atmospheric conditions such as temperature and pressure.Atmospheric turbulence causes random fluctuation of atmospheric refractive index,which distorts the phase of the beam in the propagation process,thus generating crosstalk signals and damaging the quantum information encoded by OAM.Therefore,it is of great significance to study the dynamics of quantum information resources encoded by OAM photons in atmospheric turbulence to improve the transmission efficiency of quantum information in wireless communication and to protect quantum information resources.In this thesis,the nonclassical correlation and quantum coherence of OAM photons in atmospheric turbulence are studied.The main work is as follows.(1)The decay properties of the quantumness including quantum entanglement,quantum discord,and quantum coherence for two photonic qubits,which are partially entangled in their orbital angular momenta,through Kolmogorov turbulent atmosphere are investigated.It is found that the decay of quantum coherence and quantum discord may be qualitatively different from that of quantum entanglement when the initial state of two photons is not maximally entangled.We also derive two universal decay laws for quantum coherence and quantum discord,respectively,and show that the decay of quantum coherence is more robust than nonclassical correlations.(2)The effects of non-Kolmogorov atmospheric turbulence on the transmission of OAM single photons for different turbulence aberrations in optical communication are explored via the channel capacity.For non-Kolmogorov model,the characteristics of atmosphere turbulence may be determined by different cases,including the increasing altitude,the mutative index-of-refraction structure constant and the power-law exponent of non-Kolmogorov spectrum.It is found that the influences of low-order aberrations,including Z-tilt,defocus,astigmatism,and coma aberrations,are different and the turbulence Z-tilt aberration plays a more important role in the decay of the signal.(3)The non-horizontal distributions of OAM biphotons through free-space atmospheric channels are discussed,in which case the non-Kolmogorov turbulent effects shall be considered.It is found that universal decay laws of entanglement and discord also exist for non-Kolmogorov turbulence but with their decay curves different from that of entanglement for Kolmogorov turbulence.We show that the universal decay laws are dependent on the power-law exponent of the non-Kolmogorov spectrum and compare the differences of decay properties between entanglement and discord caused by non-Kolmogorov turbulence. |
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