利用光前置放大器改进连续变量量子密钥分发系统
Improvement of continuous-variable quantum key distribution systems by using optical preamplifiers
摘要：
连续变量量子密钥分发协议，基于高斯调制的正交相干态，已经在最近的实验中实现。这种系统目前的限制是检测器的有限效率，这在原则上可以通过使用经典的光前置放大器来补偿。在这里，我们详细研究这种可能性，推导出修改后的密钥生成速率时，光学参量放大器被放置在输出的量子信道。在提出了一套一般的安全证明后，我们表明，使用前置放大器补偿所有的缺陷时，放大器是最佳的增益和噪声的检测器。在实践中通常满足的条件下，不完美的放大器也可以提高系统性能。
英文摘要：
Continuous-variable quantum key distribution protocols, based on Gaussian modulation of the quadratures of coherent states, have been implemented in recent experiments. A present limitation of such systems is the finite efficiency of the detectors, which can in principle be compensated for by the use of classical optical preamplifiers. Here we study this possibility in detail, by deriving the modified secret key generation rates when an optical parametric amplifier is placed at the output of the quantum channel. After presenting a general set of security proofs, we show that the use of preamplifiers does compensate for all the imperfections of the detectors when the amplifier is optimal in terms of gain and noise. Imperfect amplifiers can also enhance the system performance, under conditions which are generally satisfied in practice.
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