Efficient and Versatile Fiber-based Quantum Photonic Sources

量子光子源之于量子技术就像激光之于光学技术。在激光发明后的50年里，激光已经从实验室的好奇心变成了日常生活中的必需品。它的应用范围从DVD播放器到工业切割和焊接，从激光手术到远程通信。事实上，没有激光就不可能有互联网。类似地，在不久的将来，量子光子源很可能扮演与激光同样重要的角色。它们产生的光子表现出经典粒子无法模仿的量子相关性。利用量子相关性可以实现经典方法无法实现的功能，例如通信中的无条件安全、量子计算中的高效算法和量子成像中的超高分辨率。*基本量子光子源产生纠缠光子对，广义上讲，是在特殊量子状态下制备的光子对（或光粒子），使它们表现出相关特性。例如，对于偏振纠缠的光子对，测量一个光子的偏振态可以揭示它的同伴的偏振态，即使它们在物理上彼此相距很远——爱因斯坦曾将这种现象描述为“幽灵般的超距作用”。*正是这种“怪异”或非直觉性激发了量子资源的非常规使用。例如，基于纠缠的量子密钥分发（QKD）利用发送给两个远程方的光子的相关性，并允许它们共享一组通用的随机加密密钥。它保证了密钥的安全性，因为任何窃听尝试都会导致可检测到的相关性恶化。纠缠光子也被用于构建许多其他类型的量子光子源，如预告单光子源、多光子纠缠源等。它们是量子计算、量子通信、量子计量和量子光刻的基本工具。在此，我们建议利用光纤开发一种高效、通用的量子光子源。非线性光学材料中的高能量光子可以产生纠缠光子对。由于光纤的弱非线性，它在这方面的效率很低。我们建议使用极化光纤，一种已经受到高电场，有效地产生纠缠光子对。紧凑、坚固、基于光纤的光源非常适合使用光纤进行传输或光子传输的QKD和计量应用，因为它们消除了光束对准的需要，消除了光纤之间的耦合损耗，并为现场部署提供了完美的交钥匙操作。*量子技术将在21世纪发挥重要作用。量子光子源在许多量子应用中是必不可少的。本提案旨在为实际应用的量子技术的发展迈出重要的一步。

Quantum photonic sources are to quantum technology what lasers are to optical technology. In the 50 years after the invention of laser, lasers have emerged from a laboratory curiosity to a necessity in everyday life. Its applications cover everything from DVD players to industrial cutting and welding, from laser surgery to long-distance communication. Indeed, the Internet would not have been possible without lasers. Analogously, quantum photon sources will likely play an equally important role as lasers do in not too distant future. They produce photons exhibiting quantum correlations that cannot be mimicked by classical particles. The quantum correlations can be harnessed to perform functions impossible to achieve classically, such as unconditional security in communication, efficient algorithm in quantum computing, and ultra-high resolution in quantum imaging.* A basic quantum photonic source produces entangled photon pairs, which, broadly speaking, are pairs of photons (or light particles) prepared in a special quantum state that makes them exhibit correlated properties. For example, for polarization-entangled photon pairs, the measurement of one photon's polarization state reveals that of its partner, even when they are physically far away from each other-a phenomenon once described by Einstein as "spooky action at a distance".* It is this "spookiness", or non-intuitiveness, that inspired the unconventional usage of the quantum resource. Entanglement-based quantum key distribution (QKD), for example, utilizes the correlation of the photons sent to two remote parties and allows them to share a common set of random cryptographic keys. It guarantees the security of the keys since any eavesdropping attempt would result in a detectable deterioration of correlation. Entangled photons are also used to construct many other types of quantum photonic sources, such as heralded single photon sources, multi-photon entanglement sources, etc. They are essential tools for quantum computing, quantum communication, quantum metrology, and quantum lithography. * Here we propose to develop an efficient and versatile quantum photonic source using optical fibre. Entangled photon pairs can be generated from higher energy photons in a nonlinear optical material. Optical fibre is typically inefficient for this purpose due to its weak nonlinearity. We propose to use poled fibre, one that has been subject to a high electric field, for efficient entangled photon pair generation. Compact, robust, fibre-based sources are highly desirable for both QKD and metrology applications that use fibre for transmission or photon delivery, because they remove the need for beam alignment, eliminate coupling losses to and from fibre, and facilitate turn-key operation perfect for field deployment.* Quantum technology will play an important role in the 21st century. Quantum photonic sources are essential for many quantum applications. This proposal aims to take an important step forward in the development of quantum technology for practical applications.