| In classical and quantum theory,the randomness of physics is one of the key factors in the application of information technology and cryptography.Because secure encryption and communication systems are based on true randomness,high-speed true random number generators provide the necessary preconditions for cryptographic systems and secure communication.The largest feature of quantum random numbers is the intrinsicrandomness which can be proved in information theory,and the randomness is based on the uncertainty of quantum physics.The single measurement result is completely random and unpredictable,which follows the basic laws of quantum mechanics.In the past two decades,various types of quantum random number generators have emerged,and related research has developed rapidly.However,since the method of generating quantum random numbers is derived from the measurement of microscopic quantum properties of the optical field,the generation rate of quantum random numbers is limited by the physical entropy source and the detector bandwidth,which is lower than the current fiber transmission rate,and thus it is difficult to be compatible with the optical fiber communication rate,which becomes a major obstacle in the practical quantum key distribution and communication applications.Therefore,how to effectively increase the generation rate of quantum random numbers has become one of the urgent problems to be solved.In the existing quantum random number generation schemes,the device-independent quantum random number method based on the quantum fluctuation of the vacuum state shows a unique advantage.The vacuum state is a pure quantum state with the lowest energy and independent of external physical quantity.It is not subject to the association or control of the attacker,so true random numbers can be generated by measuring the vacuum quadrature amplitude.Vacuum quantum noise is an ideal white noise,theoretically has an infinite bandwidth,and there is no correlation between different spectra.Meanwhile,the measured vacuum quadrature amplitude component is a continuous variable,the measured value of which is updated infinitely fast,so a large number of random bits can be extractedfrom a single measurement.Therefore,the vacuum state quantum noise can be used to obtain true random numbers with single-valued,non-reproducible and uncorrelated manipulation.At the same time,the method of extracting quantum random numbers based on the orthogonal component of the vacuum state still has a large speed-up space,and a good application prospect in quantum communication.In addition,due to the simpler experimental device and the fact that balanced homodyne detectors can work efficiently at room temperature,with improved detection bandwidth,reduced limiting conditions,and high operability,which makes it easier to integrate and can be applied to practical chip production.The entropy content of a random sequence is a quantitative measure of its randomness or unpredictability,and is also an important parameter for extracting random characteristics from the original signal.However,the current methods for evaluating random numbers are tests in the digital domain for binary digital signals of “0” and “1”,whichthe pseudo-random numbers generated by computer algorithms can also pass.There is still no quantification and evaluation for the physical randomness generation process,so how to quantify whether the random number comes from the physical entropy source by evaluating the original physical signal is particularly significative.In addition,macroscopic high-dimensional chaotic laser is used for high-speed chaotic random number generation due to the characteristics of a wide spectrum and high-intensity fluctuations and long-term unpredictable characteristics,as well ashigh maturity of macroscopic horizontal optical detection systems.The problem of quantifying and extracting the randomness of macroscopic high-dimensional chaotic laser in real time still needs to be solved.Therefore,real-time quantification and security monitoring of physical entropy sources are particularly important in random number generation and secure communication applications.In view of the above problems,the main work of this paper is as follows:1)A balancedhomodyne detection system based on vacuum state quantum fluctuations is constructed.The measurement of continuous variable quantum noise,evaluation of minimum conditional entropy of quantum randomness,and the effective improvement and extraction of quantum noise entropy content are analyzed theoretically and experimentally.From the perspective of enhancing quantum entropy,the growth process of quantum entropy of homodyne gain under the optimal dynamic analog-to-digitalconversion range is studied theoretically and experimentally,thereby significantly increasing the quantum random bit rate;2)Theoretically and experimentally,the original microscopic quantum shot noise of physical entropy source and the macroscopic high-dimensional chaotic simulation signal are quantitatively evaluated.A method for measuring randomness by the entropy rate is proposed and the entropy growth rate of the physical entropy source is directly measured.In addition,in the process of generating random numbers by using chaotic laser,there is an external cavity time delay feature,and it has to be effectively suppressed to facilitate the application of chaotic random number generation and secure communication.Experimental and theoretical results show that the band extraction can effectively suppress the delay characteristics of chaotic laser.The suppression ratio is 95% compared with the original chaos and delay characteristic value is reduced to 0.015.The relationship between the entropy rate and the time delay characteristics of the chaotic laser after frequency-band extraction under different attenuation intensity and bias current conditions is studied experimentally.The entropy rate metric provides a feasible solution for quantifying the randomness of physical entropy sources in real time. |
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