Engineering Quantum Entanglement

量子技术正在成为21世纪世纪创新的引擎。量子技术中的一个关键组成部分是量子纠缠源，它产生纠缠粒子，通常是纠缠光子。这些光子表现出很强的相关性，这是经典粒子无法模仿的。例如，对于偏振纠缠的光子对，测量一个光子的偏振态就可以揭示出它的伙伴的偏振态，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“诡异”或非直觉性激发了量子纠缠的非传统用法。例如，基于纠缠的量子密码学利用发送到两个远程方的光子的相关性，并允许它们共享一组公共的随机加密密钥。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的相关性恶化。量子纠缠还可以用来执行其他经典无法实现的功能，例如高效的量子计算算法和量子成像中的超高分辨率。

Quantum technologies are becoming the engine of innovations in the 21st century. A key component in quantum technologies is the quantum entanglement source, which produces entangled particles, typically, entangled photons. These photons exhibit strong correlations that cannot be mimicked by classical particles. 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 quantum entanglement. Entanglement-based quantum cryptography, 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. The quantum entanglement can also be harnessed to perform other functions impossible to achieve classically, such as efficient quantum computing algorithms and ultra-high resolution in quantum imaging.