| Quantum key distribution is one branch of quantum secure communication with great potentiality. It is the product of the combination of quantum mechanics and cryptography. More and more attention has been paid on it because of its unconditional security.We first introduce the basic quantum key distribution protocol, such as, BB84and the six state protocol in the thesis. Then we present an improved protocol of BB84and the six-state protocol using the orbital angular momentum of the photons as information carriers. We give the raw key rate and error key rate by Labview software as simulation tools. The simulation results show that they are consistent with the theoretical analysis. Finally, we describe an efficient quantum key distribution scheme based on Poincare sphere on orbital angular momentum.Beam is subject to the influence of atmospheric turbulence when it is transmitted in free space. We consider the influence of atmospheric turbulence on the proposed quantum key distribution protocol, and analyse the error key rate on the consideration of atmospheric turbulence refractive index constant and the transmission distance. The simulation results show that the quantum key distribution protocol is affected greatly by the atmospheric turbulence. In addition, We give an error correction coding method to weaken the influence of atmosphere turbulence. Here, we use (7,4) linear block code for the error correction. The simulation results show that the error key rate is decreased obviously. It can be concluded that error correction coding is an effective way to weaken the impact of atmospheric turbulence on the quantum key distribution protocol. |
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