Phootn Polarization And Entanglement Modulation For Ground-Space Channel Systems

Quantum communication theory is a new interdisciplinary subject, which is born in thefusion of communication technology and quantum physics．Quantum communication theoryhas many significant applications such as high-speed, ultra-large capacity and unconditionalsecurity in both basic theory and pratical fields. In free space quantum communication, thephoton polarization and entangled state carrying quantum information will be affected by theturbulent atmosphere in the ground-space channels and it will degrade the performance ofquantum communication system. In recent years, many experimental studies related totransfer quantum polarization information through the turbulent atmosphere have beenpublished, but the theoretical study lags behind the experimental study. In this dissertation, wegive a theoretical investigation to the quantum polarization fluctuations of complicated laserbeams and the entanglement of spatial two-qubit state propagating in a slant turbulentatmosphere channel based on quantum Stokes operators, extended Huygens-Fresnel principleand Rytov approximation method, and it will helpful for improving the performance ofquantum communication system encoding by photon polarization. The main contributions aresummarized as follows.(1) For the two types of multi-mode Gaussian beams, the Hermite-Gaussian beam andthe Laguerre-Gaussian beam, a theoretical model of quantum polarization fluctuations of thephoton beams propagation in the turbulent atmosphere is developed by using quantum Stokesoperators and extended Huygens-Fresnel principle. Furthermore, we investigate the influenceof atmospheric turbulence on the quantum polarization properties numerically based on thederived formulae, and the results show that the polarization noise can be restrain effectivelyby selecting the beams with lower order mode, higher density photons, shorter wavelengthand higher spatial coherence.(2) For the diffraction-free Airy beams, a theoretical model of quantum polarizationfluctuations of the photon beams propagation in the turbulent atmosphere is developed byusing quantum Stokes operators and extended Huygens-Fresnel principle. Furthermore, westudy the restrain ability to polarization noise induced by atmospheric turbulence of Airybeams and the results show that the quantum communication systems which select the Airybeam as the emission source can possess the stronger resilience ability than those of theGaussian beam.(3) For the multi-Gaussian Schell-model beam, an analytical formula of the quantumpolarization degree is derived under different conditions of the turbulent channel and thebeam parameters. The numerical simulations show that polarization noise can not becontrolled well in the quantum communication systems using the multi-GaussianSchell-model beams as the eimission source.(4) Based on the Rytov approximation and paraxial approximation methods, theanalytical formulae for the concurrence which is used to quantify the degree of entanglementof spatial two-qubit states of the Gaussian Schell-model and the partially coherent darkhollow pump beams in a slant turbulent channel are derived respectively. Furthermore, the changes of the concurrence induced by atmospheric turbulence are investigated numericallyunder different conditions and the numerical simulations show that the concurrence of spatialtwo-qubit states will remain close to unity as long as the magnitude of the two-photonposition-asymmetry vector is much smaller, and the entanglement will preserved well byselecting the pump beam with longer wavelength and the turbulence environment with biggerrefractive power spectrum index and inner scale in quantum communication systems encodedby spatial two-qubit states. These results may be useful for improving the performance ofquantum communication systems.