基于Sagnac环干涉仪和偏振不敏感相位调制器的量子密钥分发
Quantum key distribution based on a Sagnac loop interferometer and polarization-insensitive phase modulators
摘要：
提出了一种基于Sagnac环结构的量子密钥分发（QKD）系统的设计方案，采用了一种新的基于频移的相位调制方案，实现了BB84 QKD系统的稳定运行，具有高干扰可见性和低量子误码率（QBER）。相位调制通过将具有固定时间延迟（或固定光路延迟）的两个光脉冲发送通过频移元件并通过调制频移量来实现。在离开频移元件时两个光脉冲之间的相对相位由时间延迟（或光路延迟）和频移两者确定，并且因此可以通过改变频移量来控制。实验中采用声光调制器（AOM）作为移频元件，通过改变AOM的驱动频率来实现相位信息的编码，在单光子水平上，对40 km和10 km光纤环的干涉可见度分别为96%和99%。在40 km的Sagnac环上连续运行BB84协议1 h，QBER保持在2%~5%的范围内。我们的方案的另一个优点是，相位和幅度调制可以同时通过AOM的驱动信号的频率和幅度调制来实现，从而允许我们的QKD系统实现其他协议的能力，例如诱饵状态QKD和连续变量QKD。本文还简要讨论了双向QKD系统中一种新的ESCRENMETTING攻击策略（“相位重映射”攻击）。
英文摘要：
We present a design for a quantum key distribution(QKD) system in a Sagnac loop configuration, employing a novel phase modulation scheme based on frequency shift, and demonstrate stable BB84 QKD operation with high interference visibility and low quantum bit error rate (QBER). The phase modulation is achieved by sending two light pulses with a fixed time delay (or a fixed optical path delay) through a frequency shift element and by modulating the amount of frequency shift. The relative phase between two light pulses upon leaving the frequency-shift element is determined by both the time delay (or the optical path delay) and the frequency shift, and can therefore be controlled by varying the amount of frequency shift. To demonstrate its operation, we used an acousto-optic modulator (AOM) as the frequency-shift element, and vary the driving frequency of the AOM to encode phase information.The interference visibility for a 40km and a 10km fiber loop is 96% and 99%, respectively, at single photon level. We ran BB84 protocol in a 40-km Sagnac loop setup continuously for one hour and the measured QBER remained within the 2%~5% range. A further advantage of our scheme is that both phase and amplitude modulation can be achieved simultaneously by frequency and amplitude modulation of the AOM's driving signal, allowing our QKD system the capability of implementing other protocols, such as the decoy-state QKD and the continuous- variable QKD. We also briefly discuss a new type of Eavesdropping strategy ("phaseremapping" attack) in bidirectional QKD system.
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