半导体纳米材料相干光学特性的实验研究

The abibity of controlling and processing single photons emitted from a two-level quantum system to realize long distance transmission of encrypted binary codes is one of the main requirements for future applications of quantum information processing and communication. Compared to natural atoms, semiconducting nanomaterials of self-assembled quantum dots, colloidal quantum dots and single-walled carbon nanotubes have much larger optical transition dipole moments. Moreover, their structural properties such as shape, size, density, position and composition can be effectively controlled, which is important for the purpose of flexibly adjusting their electronic and optical properties. In this project, we plan to study the quantum coherent properties of the above three material systems on the single molecule level and promote their device applications in single photon sources. For self-assembled quantum dots, we will study their microcavity quantum electrodynamics to observe more novel quantum coherent properties; for colloidal quantum dots, we will try to measure their basic quantum coherent properties of quantum interference and Rabi oscillations for the first time; for single-walled carbon nanotubes, we will measure their single photon emissions to solve the long-existing problem of whether they are two-level quantum emitters at room temperature. When this project is done, we hope to publish several journal papers with important international influence and establish a world-class group in the nano-optics research area.

能够对两能级量子系统产生的单光子进行处理和控制，来实现长距离传输二进制编码的保密数据是实现未来量子信息处理和通讯的必要条件。与自然原子相比，以外延生长量子点、胶体量子点和单壁碳纳米管为代表的半导体纳米材料具有较大的光学跃迁偶极矩，而且其形状、尺寸、密度、位置和组成等参数在生长过程中都能够得到有效的控制，从而达到灵活地调节其电光特性等目的。本项目计划对上述这三种半导体纳米材料在单分子精度进行量子相干特性的测量和单光子器件的研制。在外延生长量子点方面，将结合微腔量子电动力学来观察到更多新奇的量子相干特性；在胶体量子点方面，争取首次实现量子干涉和Rabi振荡这些基本量子相干特性的测量；在单壁碳纳米管方面，通过单光子发射的测量，来解决其在室温条件下是否为两能级量子发光体这个问题。项目完成时，力争发表若干具有重要国际影响的学术论文，建立具有国际先进水平的半导体纳米材料光学特性研究团队。

本项目的主要研究方向是半导体纳米材料的单光子发射和相干光学特性，所研究的材料体系集中于自组织InGaAs量子点、胶体CdSe量子点和胶体钙钛矿量子点。在2014年主要研究了：1）平面微腔内系综自组织InGaAs量子点的高效上转换荧光现象，通过理论计算将其归结为量子点间的相干作用以及微腔对自发辐射速率进行调制所产生的综合效应；2）合成了由单个胶体CdSe量子点和多个染料分子组成的能量转移颗粒，实现了双波长单光子发射。在2015-2016年主要研究了：1）单个自组织InGaAs量子点在单光子发射过程中的荧光闪烁现象，揭示了处于吸收态和发射态的电子与周围缺陷的作用机制；2）在单个胶体CdSe量子点中观察到带电双激子发射，揭示了其发射荧光寿命不可区分光子对的特性；3）合成了胶体钙钛矿量子点，发现了其具有超大吸收横截面积和超短荧光寿命的单光子发射特性。4）首次实现紫外光激发下对单个CdSe量子点荧光特性的测量，并且在单量子点精度观察到载流子倍增效应。项目进行的两年中，共发表7篇SCI文章，包括Physical Review Letters 1篇，ACS Nano 2篇，Scientific Reports 2篇和Applied Physics Letters 2篇。