Measurement-Device-Independent Quantum Key Distribution (MDI QKD)

量子密钥分配是目前最有吸引力的安全交换密钥的方法。它通过提供基于量子力学原理的理论安全性来消除当前经典密钥分发方法的漏洞。然而，在现实世界的实现中，由于所使用的设备的不完美性质，QKD容易受到信息窃取攻击。MDI QKD消除了对安全检测站的需要，这被认为是QKD系统的主要漏洞，通过将其转换为传输站。然而，它需要准备几乎完美的状态和使用高计数率的单光子探测技术。先前在工程部门和东芝CRL内部进行的工作已经成功地报告了方法，通过原理证明演示，满足了强加的限制并产生了高密钥速率。这些方法包括利用增益开关种子激光器作为一种方式来创建弱相干脉冲，几乎完美地干涉和自差分雪崩光电二极管和超导纳米线单光子探测器的高密钥速率和效率在室温下。该项目将集中在MDI QKD系统的设计和优化基于以前的研究，为真实的生活的实施。在这个概念中有大量的参数会发生变化。该项目的目的是考虑到MDI QKD在真实的情况下的限制，以改进当前的文献，同时改进和表征所使用的光电子学。需要解决的主要问题之一是有用的MDI QKD的传输距离的戏剧性和不可避免的增加。这使系统工作的条件恶化，因此需要开发具有高稳定性的反馈回路。此外，使用主时钟的源和接收器的同步是不可行的，并且需要设计替代方法，例如利用多路复用。实现的MDI QKD的关键特征是具有真实的时间数据分析和状态调制的自动性。因此，开发一个代码，将驱动适当的光电元件的功能和重新校准仪器在运行期间是强制性的。还非常重要的是，真随机数发生器用于选择碱基、比特和由协议施加的任何其他参数。这些发生器利用物理现象，通常是量子性质，已知是随机的，因此保证其输出是完全不相关和不可预测的。应研究真正的随机数生成方法，以推导出适当的方法，优化系统的关键率、成本、效率和规模。最后，原理证明演示不包括对特洛伊木马等可能攻击的保护，使其不适合商业化。因此，研究的目的不仅仅是在现场条件下优化系统，还可以提高系统的安全性，防止黑客攻击。根据工作的进展和结果，可以研究各种进一步的想法。这些概念包括系统的光子集成或其发展成多个源的星星形网络。然而，该项目的共同目标仍然是量子光学和信息研究领域。

QKD is currently the most appealing approach for the secure exchange of a secret key. It removes the vulnerabilities of current classical key distribution methods by providing theoretical security based on the principles of quantum mechanics. However, in real-world implementations, QKD is susceptible to information stealing attacks due to the imperfect nature of the devices utilised. MDI QKD removes the need for a secure detection station which is believed to be the main vulnerability of QKD systems, by transforming it into a transmission station. It however requires the preparation of almost-perfect states and the use of high count rate single photon detection technologies. Previous work carried out within the Engineering Department and Toshiba CRL, has successfully reported methods, via proof-of-principle demonstrations, that satisfy the imposed limitations and produce high key rates. Such methods include the utilisation of gain switched seeded lasers as a way of creating weak coherent pulses that almost perfectly interfere and of self-differencing avalanche photo diodes and superconducting nanowire single photon detectors for high key rates and efficiency at room temperatures.The project will be focused on the design and optimisation of an MDI QKD system based on previous research, for real life implementation. There is a vast amount of parameters that change in this concept. The aim of this project is to take account of the restrictions of MDI QKD in real situations to progress the current literature, while improving and characterising the optoelectronics used. One of the main issues that needs to be countered is the dramatic and inevitable increase of transmission distances for useful MDI QKD. This deteriorates the conditions under which the system operates and therefore necessitates the development of feedback loops with high stability. Additionally, the synchronisation of the sources and the receiver using a master clock is not viable and alternative methods need to be devised, for example utilising multiplexing. A crucial feature of an implemented MDI QKD is automaticity with real time data analysis and state modulation. Consequently, the development of a code that will drive the suitable optoelectrical components to function and recalibrate the instruments during the run period is mandatory. It is also very significant that true random number generators are used for the selection of bases, bits and any other parameters imposed by the protocols. These generators exploit physical phenomena, usually of quantum nature, that are known to be random and therefore guarantee that their output is completely uncorrelated and unpredictable. Research into true random number generation methods should be carried out to deduce the appropriate method that will optimise the key rates, cost, efficiency and size of the system. Finally, the proof-of-principle demonstrations do not include protection against possible attacks like the Trojan horse, rendering them unfit for commercialisation. Therefore the purpose of the research is not solely to optimise the system under field conditions but additionally to increase its security against hacking attempts.There are various further ideas that could be researched, depending on the progress and outcomes of the work carried out. Such concepts include the photonic integration of the system or its development into a star shaped network of multiple sources. The collective aim of the project however, remains within the quantum optics and information research area.