Research On Characteristics Of Practical Quantum Communication System

Quantum information science is the product of the cross-combination of quantum theory and information science.It has created a new way of communication and information processing.It has huge advantages that traditional method cannot match.And it will be applied on a large scale in future urban networks.Reference-frame-independence quantum key distribution(RFI-QKD)is a promising protocol for unconditionally and securely transferring keys between two remote users without the need to calibrate slowly changing reference frames.The performance of RFI-QKD at 1310nm and 1550nm is compared,including not only misalignments of reference frames,polarization mismatch rate and background count rate,but also the tolerance of polarization mismatch rate and background count rate.In addition,optimal intensity at different distance is also discussed.This numerical simulation will provide a useful reference for the practical RFI-QKD.Reference-frame-independent measurement-device-independent quantum key distribution(RFI-MDI-QKD)is a safe approach for practical quantum communication.The detector side channel attacks could be removed without aligning the reference frames.By considering the statistical fluctuations,background counting rate and the polarization misalignment fluctuation,the performance of the RFI-MDI-QKD is analyzed under the condition of one,two and infinite decoy states.Moreover,the numerical simulation results are presented which offer significant reference for practical applications of RFI-MDI-QKD.Compared to the traditional BB84 quantum key distribution(QKD)protocol,twin-field quantum key distribution(TF-QKD)can increase the distance of key rate and break the Pirandola-Laurenza-Ottaviani-Banchi(PLOB)limit.TF-QKD has proven to be practical and secure,and its key rate is proportional to the square root of the transmission rate.Here,The influence of different phase slices on TF-QKD in the case of one decoy state and two decoy state is discussed.According to the simulation results,the optimal M for short distance and long distance is different.At the same time,the key rate between one decoy state and two decoy state as a function of distance according to the optimal M is compared.The thesis has great significance for the study of actual TF-QKD.We further study the performance of quantum key distribution based on WDM networks in practical quantum communication systems,combining QKD,RFI-QKD and TF-QKD protocols to simulate various parameter changes in a WDM QKD network.Then we discussed the performance indicators of multi-user star network and ring network under WDM conditions.For detection systems in practical quantum communication,the absorption can be amplified by using tungsten silicide(WSi)and metallic nano-antennas,which is related with the detection efficiency of a superconducting nanowire single-photon detector based on surface plasmons.A metal slot sandwiched between two hydrogen silsequioxane(HSQ),WSi nanowire,and metallic fan nano-antennas are the elements of the proposed single-photon detector.The slot is also filled with HSQ and WSi nanowire is inserted in the top of the slot.Metallic fan nano-antennas are added to nanowire and all these elements are deposed on the sapphire substrate.Our results show that the absorption/the detection efficiency of our proposed structure is much larger than the one with the niobium nitride(NbN)nanowire.There is an optimal width of WSi nano wire and the distance between WSi nano wire and metallic nano-antennas for the absorption/the detection efficiency of the detector.Our structure provides suitable parameters for designing SNSPD in experiments.