半导体锁模激光共振激发微柱耦合单量子点发射高品质单光子研究

Self-assembled single InAs quantum dots (QDs) are desired materials to fabricate real single photon sources (SPSs). QD-SPSs have been used in quantum information demonstration, overcome QD wavelength limit and realized modulated output via nonlinear frequency conversion, which shows a great influence on quantum information. For application, the indistinguishibility of QD single photons needs improvement. In recent years, by using Pulsed Resonant Excitation (PRE) technique, international scientists overcame the drawbacks of above-bandgap excitation and realized definite, high-purity, indistinguishable single photon emission in single QDs. The light source for PRE (i.e. Ti:sapphire femtosecond-pulsed laser) is yet huge and complex, far away from application. Semiconductor mode-locked laser diodes are compact in size and easy to use, which can generate picosecond laser pulses in repetition frequency of GHz or more, suitable for RRE light source. Besides, the laser diode and QD-SPS can be integrated, avoiding to use comlex optical route and promising for compact easy-to-use high-quality SPSs. In this project, we will fabricate wavelength-matched semiconductor mode-locked laser diodes and micro-pillar-coupled QD-SPSs, and integrate them togther to realize the PRE. We will study its improvement on the purity, indistinguishibility, and definity of single phhoton emission.

自组织InAs单量子点是制备真正单光子源的理想材料。国际上已将量子点单光子源用于量子通信演示，并通过非线性频率转换突破量子点波长限制、实现调制输出，在量子通信领域产生巨大影响。为实现应用，量子点单光子全同性还需提高。近年来，国际上采用脉冲共振激发技术克服了带上激发的不利影响，在单量子点上获得确定性、高纯度、全同性单光子发射。其脉冲共振激发光源（即钛宝石飞秒脉冲激光器）庞大复杂，离应用还遥远。半导体锁模激光器器件小巧、工作方便，能产生皮秒脉冲激光，重频在GHz以上，适于作为脉冲共振激发光源。而且，激光器与单光子器件可近场结合，避免使用复杂光路，有望实现小型化易操作高品质单光子器件。本项目将研制波长匹配的量子点锁模激光器和微柱耦合单量子点结构，并将两者结合，实现共振激发，研究其对单光子纯度、全同性、确定性的改善作用。

本项目基于近年来国际上在脉冲共振激发单量子点产生确定性、高纯度和全同性单光子方面的研究进展，提出开展DBR（分布布拉格反射镜）微柱腔耦合单量子点制备和单光子发射特性研究，优化单量子点生长，制备波长匹配DBR微腔和微柱阵列，确定腔模和品质因子，研究其对量子点单光子发射纯度、光谱的影响；研制半导体可调谐激光+射频信号源直接调制，取代常用的体积庞大的钛宝石飞秒激光器用于共振激发单量子点，研究单量子点共振荧光的单光子性和全同性。已取得结果：获得了密度可控单量子点长期稳定生长参数，掌握了量子点片上分布规律，提高了片上可用单点区面积，采用应力耦合双层点结构将单量子点波长拓展到1.3微米。掌握了DBR微腔精确校准技术，制备出DBR微柱耦合单量子点，并用光刻+等离子体深刻蚀批量制备微柱阵列，优化了微柱侧壁陡直度、平滑度，实现了腔模耦合Purcell增强并观察到Rabi分裂。实现了微柱耦合单量子点的光纤粘和、单光子光纤直接输出，其稳定、高效、便于实用。研制出Littrow式外腔可调谐激光器，实现0.07nm窄线宽、uW级功率、901-918nm波段可调谐连续激光输出（脉冲激光还未实现），采用可调谐激光共振激发单量子点和偏振消光，单量子点共振荧光信号较弱，仍有背景激光残留，需用FP标准具进一步滤除。项目研究获得的研究成果主要是发表论文、申请专利等。本项目的研究将为量子点单光子源在量子信息领域的应用奠定技术基础。