基于量子变频技术的可波分复用单光子源

The Quantum Frequency Conversion (QFC) technique has been widely applied in the construction of quantum network. These applications can be attributed as two aspects: The first one focuses on the quantum repeater, and through QFC the photons can be constant with the memory system (such as atomic ensemble and rare earth, et al.)in frequency and linewidth.The second one focuses on the compatibility with the current optical-fibre communication devices,in which it is necessary to converse the photon frequency to telecom wavelength. The realization of single photon source for optical-fibre communications is very important in the realization of quantum network, whereas it is very difficult to prepare such sources directly. With QFC, we can converse the photons in other wavelengths to telecom wavelengths. In this project, through QFC in PPKTP waveguide, we converse the single photons at 775nm to 1550nm telecom wavelength, creating wavelength division multiplex (WDM) single photon source. Compared to other similar proposals, our scheme is much less complicated, while the efficiency and signal to noise ratio are much higher. In additional, the wavelength tunability makes it more useful in quantum network.

近些年来，量子变频技术在构建全量子网络的一系列实验研究中得到了广泛的应用。这些应用一般可分为两个方面:一是以实现量子中继为目标,让光子体系和其他存储体系(比如原子体系,稀土原子等等)能在频率和线宽上匹配;二是为了满足量子网络中光纤传输的需要,也就是把需要把光子的频率转化到通讯波段。实现通讯波段的单光子源对于量子网络的最终实现是有重要意义的,而以现有的实验技术直接制备这样的光源是相当困难的。量子变频技术使得我们可以把其他波段的单光子源以相当高的效率转换到通讯波。在该项目中,我们将以现有的775nm量子点单光子源为基础,与经典的1550nm激光通过PPKTP晶体相互作用,实现可波分复用的1550nm波段单光子源。和国际上类似的方案相比，该项目实验装置复杂度明显降低的同时，可以拥有更高的转换效率和信噪比，更重要的是输出波长可调，因而实用性明显提高。

本项目将目前比较成熟的半导体量子点体系和非线性晶体结合起来，用来制备确定性的通讯波段单光子源和纠缠光源。这个方案充分利用了量子点确定性单光子发射和非线性晶体波长自由度大的优点。采用我们国家研究小组自己生长的超高亮度纳米线量子点样品和高转化效率的周期性极化晶体，利用量子光学实验领域最新的sagnac干波环技术，产生1550nm确定性偏振纠缠的光子对。光子对中的任何一个光子都可以当作单光子源使用。该方案第一次将固态和光学系统结合起来，起到扬长避短的作用，是制备实用化通讯波段量子光源重要的一步。