Research On Quantum Classical Channel Multiplexing And Source Independent Security Of Continuous Variable Quantum Key Distribution With Entangled States

With the rapid development of science and technology,more and more people pay attention to information security.Quantum key distribution(QKD)is an important branch of quantum information.Based on the basic principles of quantum mechanics,it can provide theoretical unconditional security for both parties of communication.Eavesdroppers can’t get any information without being found.A successful quantum key distribution process can make legitimate communication parties share a set of security keys.Among the different classification protocols of QKD,continuous variable quantum key distribution(CV-QKD)based entangled state has the advantages of strong resistance to excess noise,inherent source independent security,compatibility with existing optical fiber networks,and the use of mature balanced homodyne detector(BHD)technology.Moreover,photon entanglement has the potential of long-distance expansion,which is expected to realize a wide range of quantum networks in the future.Based on the above development potential,we first establish a stable long-distance CV-QKD based entangled state experimental system by continuously optimizing the system,and then further promote the development of entangled continuous variable quantum key distribution experiment from three aspects of practicability,security and high speed.The main research contents and innovations of this paper are as follows:1.The key distribution experiment of continuous variable EPR entangled state transmission of 50 km is realized.Firstly,a four mirror butterfly resonator with a nonlinear periodically poled KTiOPO4(PPKTP)crystal is used to generate a two-color continuous variable entanglement source with high entanglement.One 810 nm beam is left at the local Alice’side for measurement,and the quantum information it carries can be stored on the local quantum storage carrier(such as Rb atom)in the future;the other 1550 nm beam is used for long-distance transmission of quantum information.By optimizing the system,we use key techniques to ensure the stable and optimal operation of the entangled state CV-QKD.At the measurement side,we use DAQ high-speed acquisition card to collect the quadrature values of the optical field.After a series of data processing,we get that after 50 km transmission in the standard optical fiber,the entanglement of the sum of the phase quadrature and the difference of the amplitude quadrature components still reach-0.315 dB and-0.354 dB,which meet the EPR criterion,indicating that the dual-mode shared by Alice and Bob is still entangled state.This experiment is more secure than the coherent state CV-QKD with simultaneous distance.2.The entangled state CV-QKD is implemented in dense wavelength division multiplexing(DWDM)with five channels of classical light whose adjacent channel spacing is 100 GHz.The transmission power of each channel is 2 mW,and the nonreturn-to-zero on-off-keying(NRZ OOK)modulation rate is 2.5 Gb/s and 10 Gb/s.During the experiment,we first analyze the excess noise sources that are easily introduced into the quantum channel in the process of coexistence of classical light and quantum signal.It is worth noting that when the communication distance is short,four wave mixing noise will become the main excess noise source in the quantum system,which seriously affects the generation of security key rate.Therefore,we establish a theoretical calculation model of excess noise generated by four wave mixing noise,and verify its correctness from experiments.Finally,the classical channel unequal frequency spacing technique is used to eliminate the influence of four wave mixing noise,so as to realize the coexistence of long-distance entangled state CV-QKD and strong classical light.3.Through the experiment of entangled state source independent CV-QKD,Alice and Bob can share the security key under the condition that the entangled source is not trusted,which further improves the practical security of entangled state CV-QKD system.We select the entanglement source parameter with the highest key generation rate,adjust the random measurement ratio of amplitude and phase quadrature to 0.1:0.9,and obtain the security key rate of 0.0034 bits,0.0058 bits and 0.021 bits per pulse respectively when the combination of Charlie to Alice equivalent distance and Charlie to Bob transmission distance is(0 km,60 km),(1 km,40 km)and(2 km,20 km).4.The signal-to-noise ratio of time-domain BHD is calculated theoretically.The RLC high pass filter circuit is designed to significantly improve the pulse repetition rate and suppress the electronic dark noise.The parameters of the amplifier are adjusted and the feedback circuit of the charge amplifier is designed carefully.Then the signal-to-noise ratio is improved in the case of high-speed pulse signal.The BHD is able to measure pulse signal with high repetition rate of 40 MHz,the signal-to-noise ratio is 14.5 dB when the number of photons per pulse is 9.9×107.The BHD provides an indispensable measurement device for high-speed CV-QKD system.