Title: Highly Efficient and Broadband Optical Delay Line towards a Quantum Memory Show Chinese title

Title: 面向量子存储器的高效宽带光延迟线

Abstract: We demonstrate a high-efficiency, free space optical delay line utilizing a nested multipass cell architecture. This design supports extended optical paths with low loss, aided by custom broadband dielectric coating that provides high reflectivity across a wide spectral bandwidth. The cell is characterized using polarization-entangled photon pairs, with signal photons routed through the delay line and idler photons used as timing reference. Quantum state tomography performed on the entangled pair reveals entanglement preservation with a fidelity of $99.6(9)\%$ following a single-transit delay of up to $687$~ns, accompanied by a photon retrieval efficiency of $95.390(5)%$. The delay is controllable and can be set between $1.8$~ns to $687$~ns in $\sim12.6$~ns increments. The longest delay and wide spectral bandwidth result in a time-bandwidth product of $3.87\times 10^7$. These results position this delay line as a strong candidate for all-optical quantum memories and synchronization modules for scalable quantum networks. Show Chinese abstract

Abstract: 我们展示了一种利用嵌套多通光路结构的高效自由空间光延迟线。 该设计通过定制的宽带介质涂层，提供了宽光谱带宽内的高反射率，从而支持低损耗的延长光路。 通过偏振纠缠光子对对单元进行表征，信号光子通过延迟线，闲频光子用作时间参考。 对纠缠光子对进行量子态层析成像，显示出在单次通过延迟后，保真度为$99.6(9)\%$，延迟时间高达$687$~ns，同时伴有光子检索效率为$95.390(5)%$。 该延迟是可控制的，可在$1.8$~ns至$687$~ns之间以$\sim12.6$~ns的增量设置。 最长延迟和宽光谱带宽导致时带宽积为$3.87\times 10^7$。 这些结果使该延迟线成为全光量子存储器和可扩展量子网络同步模块的有力候选。