Theoretical Study Of Continuous Variable Quantum Key Distribution Network

Quantum key distribution is a communication process which allows two distant parties to share a common secure secret key bit string,in spite of the potential eavesdroppers,the unconditional security is ensured by uncertainty principle and no-cloning theorem of quantum physics.There are two branches of quantum key distribution: discrete variable and continuous variable.Discrete variable schemes can get high reconciliation efficiency and long transmission distance,but pricy single photon detectors are needed and secret key rate is relatively low.By comparison,continuous variable schemes are more practical which enjoy merits including high secret key rate,mature technology of required devices and low cost,although outperformed by discrete variable counterpart in reconciliation efficiency and transmission distance.In this thesis,schemes of continuous variable quantum key distribution networks are studied.We have studied three schemes.The first one is continuous variable quantum key distribution network based on microwave photonics,we analyze its performance in point-to-point regime,show its advantages that local oscillator light is not required transmission from the sender and phase noise can be cancelled.We also propose to extend this point-to-point scheme to quantum network by means of polarization division multiplexing and orthogonal frequency division multiplexing,and illustrate their practicability.The second one is code division multiple access continuous variable quantum network using chaotic phase shifters,thanks to the orthogonality of chaotic phase shifter,the quantum network is robust against channel loss,excess noise and crosstalk.The third one is point-to-multipoint broadcast continuous variable quantum key distribution network,in this scheme the sender reconcile with different receivers in order,and utilizes the classical information of the former to help distill more secret key information than point-to-point one.We study the performance after using a phase sensitive amplifier before detection,showing further secret key rate improvement.The above three schemes are all of good practical value and pave the way for further study in quantum networks.