Continuous Variable Quantum Cryptography Communication Techniques 

Author  LuZuo 
Tutor  ZengGuiHua 
School  Shanghai Jiaotong University 
Course  Communication and Information System 
Keywords  Continuous variable quantum key distribution Quantum data stream cipher Quantum identity authentication Homodyne detector 
CLC  O431.2 
Type  PhD thesis 
Year  2011 
Downloads  159 
Quotes  0 
Quantum cryptographic as a burgeoning discipline, has changed the conventional encryption which is only dependent on mathematical and logical process, and give birth to quantum physical secure. The potential foreground and unlimited capacity of quantum cryptography have attracted a lot of funds and scientists of all of the world. As an important branch of quantum cryptography communications, the continuous variable quantum cryptography technology appeared late. However, the continuous variable quantum cryptography, which use the classical coherent light source, has a low cost, a large capacity and a high secure key rate. So it has been attracted a lot of attention since its birth. The dissertation is focused on solving some practical difficulties in the continuous variable quantum communication. Moreover, several novel and operational modulation and detection schemes are proposed.What’s more, an entire continuous variable quantum cryptography communication system prototype is realized.In order to complete the subject, the following work are presented in this paper.1. An ultralow electronic noise and pulsed balanced homodyne detector is designed and implemented. The balance of homodyne detection is calibrated rigorously. We have overcome the challenges imposed by the mismatch of photodiode response functions, insert loss and timedelay. We demonstrate that the quantum efficiency of this homodyne detector is 52.6% and CMRR is 70dB. The homodyne detector has a 17.517 dB shotnoisetoelectronicnoise ratio in the time domain at a25dBm local oscillator. The results show that the homemade homodyne detection is quantum noise limited. The performance of this homodyne detector has reached the same order of magnitude of the best homodyne detectors reported. 2. A novel polarization diversity homodyne detection scheme is proposed. We analyze this scheme with quantum operator algebra and the results show that this scheme improves the efficiency of the quantum signal receiver and eliminates the effect due to the random fluctuation of the polarization in fibre channel.3. A continuous variables quantum key distribution system is implemented over 8km optical fibre based on the go& return configuration. A secret key rate of 0.81kb/s is obtained at 100KHz. In the experiment, a polarizationindependent dual phase modulation scheme is proposed to substitute the AM&PM. The experimental results show that dynamic extinction ratio of intensity modulation is 9.5dB, the modulationnoisetoshotnoise ratio is20dB. Simultaneously, the characterization of the coexistence of quantum signal and classical signal on dense wavelength division multiplexing network is discussed in detail, too.4. A oneway continuous variable quantum key distribution scheme is realized based on the double asymmetric MachZehnder interferometers. This system achieves nearly lOkbps sifted key rate at 500KHz system clock. The security communication distance is 27.2Km, which is the longest distance reported by far. The influence of the loss, noise and environment factor on the sifted key rate of system is quantitatively discussed. The optimal modulation variance and the actual modulation accuracy are calculated in the dissertation. The channel realtime monitoring shows the system is secure practically.5. The practical security of quantum data stream cipher is discussed in detail. The channel model of quantum data stream cipher is proposed. In this model, the quantum channel connecting the two legal users is assumed to be lossy and the gaussian noise is imposed on the observed quadratures of the signal light field. The secure boundaries against beam splitter attacks are obtained based on the channel model, when Eve uses the homodyne detection and heterodyne detection, respectively. The results show that the security of system depends on practically physical parameters, then, the corresponding numerical curve is plotted. We proposes a method to use the weak coherent states to replace the classical light source in the secure data cipher system, This scheme is demonstration ex perimentally.6. We have designed and realized an continuous variable quantum cryptography integrated platform. The system use continuous variable quantum techniques to implement key distribution, data cipher and identity authentication. The platform is able to support the cipher picture, cipher text and realtime cipher voice.