Research On High Efficiency SPAD Photon Detector And Quantum Random Number Generator

Twentieth century is the century that quantum mechanics have made prominent progress in application field. The most peculiar characteristics of quantum mechanics are the existence of indivisible quanta and of entangled systems. Both of these lie at the root of quantum cryptography. Quantum cryptography could well be the first application of quantum mechanics at the single-quantum level. As the transmission of information is based on single photon, so we choose SPAD( single photon avalanche diode) as the detector. Performance of SPAD would be the vital key to decide transmission distance, error rate, and so on for the cryptography system. The key used in the one-time pad must be secret and used only once. All secure cryptosystems, both classical and quantum ones, require truly random numbers. Thus We put improving the performance of SPAD and producing truly random numbers as the two main jobs of this article.First, Designing various working circuits for SPAD to improve working performance. Passive quenching circuit is the most common working mode for SPAD in application. The two main limitations for this circuit are that the lower output amplitude of the avalanche signal which would make trouble for the latter signal executing circuit and the longer dead time (the time interval between two avalanche signals) which would make the detector lose avalanche signal, thus decreasing counting rate and lower the efficiency of detector. The main purpose of studying the high efficient SPAD is to resolve the two problems on SPAD. To improve the output amplitude, the scheme of adding AC channelduring SPAD discharge period with a little capacitance in the passive quenching circuit has realized the purpose of improving the avalanche output from 20-30mV to 120-130mV. A compact and efficient avalanche signal executing circuit has been designed to make the signal be the TTL signal to satisfy the requirement of transmission ( apply Chinese patent: 03230983. x ).A mixed passive-activequenching circuit with active fast restoring technology described in this article is to reduce the dead time and get higher counts. The single photon detector is developed successfully with higher quantum efficiency, lower noise and shorter dead time. Excellent experiment results have been got: dead time <100ns, counts>5MHz(apply Chinese patent: 03141680.2) .We do research on the autocorrelation of the output of SPAD in passive and mixed passive-active quenching modes respectively with TAC/MCA technology. And good graphs well justify our results on improving dead time with analysis on statistical time distributing of two neighboring avalanche signals (publish article on < ).Second, A quantum random number generator scheme on the basis of photon random routing chosen charactristics at a polarizing beam splitter has been justified. And A fast and compact random number generator has been produced. We well study function principle of the random number and make an investigation on the realization schemes of random number generator, both in Physics and Mathematics .Various schemes have been discussed in this article to get true random number to satisfy the requirement of quantum cryptography. Based on the random choice of a single photon at a polarizing beam splitter, a quantum Mechanical source of true random number is realized( publish article on <). To satisfy compact housings and simple to operate in practice, a fast and compact quantum random number generator has been produced in our laboratory. A compact and 10MHz modulated LD is attenuated to be approximate single photon source. High efficiency SPAD photon detector, synchronous single photon coincidence detection technique, and data collection card based on LPT port are put into practice and generating a binary random number at a rate of >1MHz/s. Perfect result on randomness has been tested by the Pseudorandom Number Sequence Test Program (ENT).Third, Doing experiment on single-photon routing control both onspace and fiber interface. As s...