近日，中国科学技术大学的周志远及其研究团队取得一项新进展。经过不懈努力，他们研制出基于叠加单片腔的窄带电信波段偏振纠缠光子源。相关研究成果已于2024年3月21日在国际知名学术期刊《物理评论A》上发表。

该研究团队成功报道了一种基于波束位移的被动稳定干涉仪技术，该技术利用两个单片非线性晶体腔，实现了单纵模光子对的叠加，进而生成窄带、电信波段、偏振纠缠的光子对。这些从空腔中产生的光子对展现出了高达20000的符合偶然符合比以及低于500MHZ的带宽。通过双光子偏振干涉、贝尔不等式验证以及量子态层析成像等手段，研究团队证明了这一纠缠源的高质量特性。相较于传统的自由空间腔增强偏振纠缠态生成方法，当前的配置展现出了更高的稳定性，为量子通信应用带来了广阔的前景。

据悉，为了避免光纤中长距离传输的频散，并能有效地与电信波段量子存储器耦合，在电信波段采用高质量的窄带偏振纠缠源是首选。

附：英文原文

Title: Narrowband telecom-band polarization-entangled photon source by superposed monolithic cavities

Author: Ming-Yuan Gao, Yin-Hai Li, Yan Li, Zhenghe Zhou, Guang-Can Guo, Zhi-Yuan Zhou, Bao-Sen Shi

Issue&Volume: 2024/03/21

Abstract: A high-quality narrowband polarization-entangled source in the telecom band is preferred to avoid frequency dispersion for long-distance transmission in optical fibers and to efficiently couple with telecom-band quantum memories. Here, we report narrowband, telecom-band, polarization-entangled photon pair generation based on the superposition of single-longitudinal-mode photon pairs from two monolithic nonlinear crystal cavities in a passively stable interferometer based on beam displacers. The photon pairs generated from the cavities exhibit a high coincidence to accidental coincidence ratio of 20000 and a bandwidth below 500 MHz. Two-photon polarization interference, Bell inequality, and quantum state tomography are performed to indicate the high quality of the entangled source. The current configuration demonstrates greater stability than traditional free space cavity-enhanced polarization-entangled state generation, which is promising for quantum communication applications.

DOI: 10.1103/PhysRevA.109.033720

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.033720