Slattery Oliver, Ma Lijun, Zong Kevin, Tang Xiao
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
J Res Natl Inst Stand Technol. 2019 Aug 22;124:1-18. doi: 10.6028/jres.124.019. eCollection 2019.
Spontaneous parametric down-conversion (SPDC) in a nonlinear crystal has been a workhorse for the generation of entangled and correlated single-photon pairs used for quantum communications applications for nearly three decades. However, as a naturally broadband process, the ability of SPDC to interface with the very narrow energy transitions in atomic ensembles for implementing quantum memories, which are needed for quantum repeaters to extend the reach of quantum communications, was initially limited. To overcome this limitation, the process was enhanced by placing the nonlinear crystal inside a resonating cavity. This modified process has some important advantages, including narrowing the spectral linewidth of generated photons into brighter resonant modes of the cavity, and the ability to lock the desired mode of the cavity to the targeted transition frequency of the atomic ensemble. This paper presents an overview of the principle of cavity-enhanced SPDC, a review of works to date using this technique, and an example of one of these implementations.
近三十年来，非线性晶体中的自发参量下转换（SPDC）一直是用于量子通信应用中生成纠缠和关联单光子对的主要手段。然而，作为一种自然的宽带过程，SPDC与原子系综中非常窄的能量跃迁进行接口以实现量子存储器的能力最初受到限制，而量子中继器扩展量子通信范围需要量子存储器。为克服这一限制，通过将非线性晶体置于谐振腔内来增强该过程。这种改进后的过程具有一些重要优势，包括将生成光子的光谱线宽变窄到腔内更亮的谐振模式，以及将腔内所需模式锁定到原子系综的目标跃迁频率的能力。本文概述了腔增强SPDC的原理，回顾了迄今为止使用该技术的工作，并给出了其中一种实现的示例。
