Real-time Reconstruction And Monitoring Of Quantum States In Quantum Random Number Generation

With the rapid development of quantum random number in the field of secure communication,in order to ensure the quality and rate of random number generation,higher requirements are put forward for the quality of entropy source,that is,to achieve more accurate characterization of the characteristics of entropy source.At present,the evaluation of entropy source mainly analyzes the macroscopic dynamic characteristics in time domain and frequency domain,such as the comprehensive use of spectrum,autocorrelation,timing,Lyapunov index,mutual information,entropy and other information.In addition,studies on quantum statistical properties have been carried out,but the quasi-probability distribution of relative phase space information needs to be further studied,which provides a necessary premise for accurate characterization of entropy sources and preparation of high-quality entropy sources in secure communication.In this paper,we further study how to reduce the system loss and the influence of non-ideal devices in the actual process,and accurately measure all the information of Wigner quasi-probability distribution in the phase space of the light field with high fidelity,and achieve97.6% high fidelity reconstruction.In view of the above problems,the research contents of this paper are as follows:(1)Firstly,this paper introduces the development status of quantum random number and phase space reconstruction technology,discusses the application of maximum likelihood method in balanced homodyne quantum tomography detection technology and the advantages of maximum likelihood method in the reconstruction of quantum state phase space,and makes specific research on balanced homodyne quantum tomography detection technology.Quantum tomography in balance homodyne detection completed on the basis of the maximum likelihood method using the quadrature data refactoring density matrix and the theoretical derivation of the Wigner function,and the entropy of the source(squeezed state,heat of chaos)phase space distribution of the Wigner function made a theoretical analysis,introduced the system loss cases Wigner function formula of the ideal,Through the definition of fidelity,it is found that the fidelity increases with the increase of the compressibility of the compressed state and the average photon number of the chaotic hot state under certain losses.(2)Analysis of experimental reconstruction results of quantum states under different entropy sources(vacuum state,amplified spontaneous emission).Firstly,the Wigner function of the vacuum state light field is reconstructed and compared with the theoretical results.The fidelity of the Wigner function is 99.5%.Maximum likelihood reconstruction process is analyzed and fidelity degrees with the change of the number of iterations,with the increase of the number of iterations,we experiment on reconstruction of density matrix is more and more close to the theory of density matrix,when the number of iterations is 2000,we experiment on the density matrix and the theory of density matrix between the fidelity of the approximate equal to 0.995;The Dephi program was used to complete the maximum likelihood iteration process,and the running time of the program increased with the increase of the range of photon number state base,data points and iteration times.In experiment and then reconstructed the amplified spontaneous emission of the Wigner function,with the increase of light intensity,measured the amplified spontaneous emission of phase space distribution compared with vacuum shot noise limit the 3,6 times magnification,respectively.(3)In experiment finally reconstructed the different states of chaotic lasers density matrix and the Wigner function,through regulating the bias current,prepared the bandwidth optical feedback intensity are 3.2 GHz quasi-periodic,7.3 GHz moderate,11.5 GHz chaotic laser coherent state of collapse,Furthermore,the density matrix and phase space Wigner quasiprobability distributions of chaotic lasers in three different states are reconstructed by balanced homodyne quantum tomography and maximum likelihood method.The phase space distributions of chaotic lasers measured are 1.5,2.5,3 times larger than that of vacuum shot noise limit.At the same time,the measurement fidelity of Wigner quasi-probability distributions in phase space of chaotic laser in three states is improved significantly from 74.9%,81.2%,84.8% to 95.5%,97.0%,97.6% after compensating the loss of the existing experimental measurement system for 9.6% during the reconstruction measurement process.