Study on quantum communication using femto-seconds pulses

我们取得了以下成果：(1)利用准相位匹配周期性轮询KTiO_4 （PPKTP）晶体获得了锁模YVO_4激光器二次谐波产生的转换效率超过40%。(2)利用飞秒Ti：蓝宝石激光器和β-BaB_2O_4晶体观察到10%的参量增益。(3)我们使用PPKTP晶体获得了10.4 dB和-3.2 dB的参数增益。(4)利用梯度折射率微透镜开发了一种光学耦合系统，使周期性轮询LiNbO_3波导具有良好的耦合效率，并观察到二次谐波的产生。(5)我们开发了一种基于商用放大器的平衡型净差探测器，利用脉冲本振可以观察真空波动。(6)利用脉冲同差检测技术实现了1公里光纤上的量子密钥分配。我们证明了基于同差检测的量子密码对于个体分束攻击是安全的。

We have achieved the following results.(1) We obtained more than 40% conversion efficiency for the second harmonic generation of a mode-locked YVO_4 laser using a quasi-phase-matched periodically-polled KTiO_4 (PPKTP) crystal.(2) We observed 10% parametric gain using a femtosecond Ti:sapphire laser and β-BaB_2O_4 crystal.(3) We obtained parametric gain of 10.4 dB and -3.2 dB squeezing using a PPKTP crystal.(4) We have developed an optical coupling system using a gradient index micro lens which enables good coupling efficiency for a periodically polled LiNbO_3 waveguide, and observed second harmonic generation.(5) We have developed a balanced homodyne detector based on a commercial amplifier with which we could observe vacuum fluctuations using pulsed local oscillator.(6) We have achieved quantum key distribution over a 1 km optical fiber using pulsed homodyne detection. We show that quantum cryptography based on homodyne detection is secure against individual beam-splitting attack.