【作者】 董春华；

【导师】 韩正甫； 郭光灿；

【作者基本信息】 中国科学技术大学 ， 光学与光学工程， 2011， 博士

【摘要】 随着人类社会的日益发展,对信息的传播和处理提出了更高的要求,而传统的计算机已经不再满足,此时,新兴的量子信息学受到越来越大的关注。量子计算作为量子信息中的研究之一,能够解决一些经典计算机无法解决的问题,具有重大的现实意义。过去的几十年,不断有各种物理方案被提出来用于实现量子计算,其中基于腔量子电动力学的方案被认为是最有希望的方案之一。它可以提供一个理想的平台进行量子态的调控,且随着微加工技术的发展,可往集成小型化方向发展,因而具有广阔的前景。本文以实现量子计算为目标,围绕微腔量子电动力学,分别对微腔以及量子点的单粒子体系展开一系列的工作,并结合两者,初步开展了腔量子电动力学的实验研究。具体有以下几个主要内容:1.搭建了固态光学微腔的实验体系该体系包括:a)可以制备出尺寸（10¹00?微米）可控的微球腔,品质因子（Q）高达10⁸以上;b)通过氢氧焰拉制的光纤锥耦合波导,最小直径可小于1微米,可以实现对各种微腔的高效耦合,其耦合效率达99%以上;c)以光纤锥耦合作为一种新的探测手段,可以实现与微球腔、微盘腔、微芯圆环腔甚至多边形微腔的各种应用。基于良好的实验制备和优秀的耦合技术,我们分别在微腔以及光纤锥的光学输运性质,后期调节以及其它应用方面开展了系统的研究。我们与国际小组分别独立观察并解释了高品质因子微球腔中的振铃现象;通过光纤锥对微腔中模式的调谐,实现了单个微腔中的类光学诱导透明;在微腔的表面涂覆上增益介质,实现了低阈值微腔激光器;我们通过后期的刻蚀和镀膜方式对微腔的模式进行了有效调制,这些调制方式将会在传感以及微腔量子电动力学的研究中得到广泛应用。此外,国际上首次通过对普通的微球腔进行CO₂激光的短脉冲处理,得到了保持高品质因子的变形微球腔,具有很好的方向性发射,在此基础上,我们对变形微球腔进行了更多性质的研究。进一步,我们还扩宽了光纤锥的应用,首次实现光纤锥对金属纳米线的有效耦合,最高的耦合效率达58%,远远高于通过自由空间光斑散射所激发的表面等离子体模式。这些方面的实验研究,奠定了我们利用微腔及其它微纳光学结构实现量子信息处理的良好基础。2.完成单光子光源的检测为了实现物质与微腔的强耦合相互作用,单个粒子体系的发光过程就很值得关注。因此,我们完成了检测单光子光源的实验体系,分别对量子点CdSe/ZnS以及金刚石中的NV色心的单光子发射进行了相应的实验研究,得到有效的单光子光源。在此基础上,将量子点分别置于二氧化硅薄膜和金膜表面,较深入的研究了不同薄膜介质对量子点的荧光衰减、荧光闪烁等产生的效应,实验发现金属表面等离子体可以提高量子点发光效率,有效压抑闪烁现象,获得的结果对在实验中实现高效率以及高质量的单光子光源很有参考意义。我们还通过单光子的检测装置,确定在微腔表面成功黏附了单量子点或单NV色心,这一结果对于我们下一步的实验中实现两者的强耦合提供了参考。3.实现微腔与量子点的耦合将量子点或含有NV色心的纳米颗粒黏附到微腔上,我们能够观察到光学腔模对发光调制的现象,即Purcell效应,这只是两者的弱耦合。为了满足两者的强耦合条件,需要在低温系统下进行实验,以降低量子点或NV色心的非均匀加宽。因此,我们将光纤锥与微腔的耦合体系转移到低温腔内,初步完成了低温下微腔对量子点发光过程调制的实验,使我们对于微腔单光子源以及基于原子与腔强耦合的量子逻辑门研究向前推进了一步。更多还原

【Abstract】 With the development of human society, the requirement of the transition and processing of information is becoming more and more prominent. At this time, the quantum information processing investigates fascinating issues at the foundations of computer science and quantum mechanics. Quantum computation, which is based on principle of coherent superposition and quantum entanglement, can solve certain problems that are hard for conventional classical computer and have great significant for our life. For decades, many physical schemes have been proposed, among which cavity quantum electrodynamics (QED) is thought to be a very promising physical system. The cavity QED, which can provide the control of quantum bit, have the bright prospects with the developing of nanotechnology and integrated on the chip. My work listed below focuses on the experiment of cavity QED which includes the whispering gallery mode microcavity and the single emitter, e.g. quantum dot (QD).1. Set up the experimental system of the microcavity and tapered fiberThe system includes: a) The microsphere is fabricated with the diameter ranging from 10μm to 100μm and the quality factor higher than 108. b) The fiber taper is fabricated by the hydrogen flame heating (with a waist less than 1μm) to effectively excite the modes in microsphere. c) With the coupling of the tapered fiber, we can use it to excite the Whisper-gallery (WG) modes in the microsphere, microdisk, microtoroid, and zeolite cylindrical microcavity with hexagonal cross section.Base on the fabrication and measurement platform, we have studied the coupling between the microcavity and tapered fiber, and the application of the microcavity especially for the cavity QED. In the high-Q microsphere, we have observed the ringing phenomena and successfully explained it in theory. We have demonstrated the EIT-like effect in a single microsphere which caused by the interference of two WG modes using the tuning of the tapered fiber. We also have got the low-threshold microlasing in the high-Q microsphere coated the Er:Yb phosphate glass layer. With the Hydrofluoric etching or polymer coating, we also have tuned the modes in the microcavity. It has wide applications in sensors and experiments of the cavity QED. In addition, we have developed the free space coupling with the deformed microsphere which is easily fabricated by the short CO2 pulse heating. It would be good for our research with the experiment of low temperature. In addition, we present the coupling of light into Ag nanowires from the fiber taper. Our demonstration offers an efficient method for the application of microcavity and promotes the realization of quantum information processing.2. Study of the single photon emitterTowards the application in cavity QED, single emitter such as quantum dot and NV center in diamond is more attractive. We have set up the Hanbury-Brown-Twiss system to demonstrate second-order correlation and detailed researched single photon emitting. CdSe/ZnS colloidal quantum dots generally exist as blinking phenomena which can be effectively modulated on the different material surface. It is shown to obviously suppress the blinking of CdSe/ZnS on the Au film. This method presents the potential application for high-speed single photon sources. We also have observed the single emitter through the HBT experiment when the QD or NV nanoparticle adopted on the surface of the microcavity.3. The coupling of QDs and microcavityWhen the QDs adopted on the surface of the microsphere, modulated photon emission from QDs have been observed, which is proved to reveal Purcell effect. It is just the weak coupling between the QDs and the microcavity. We moved the system into the low temperature. Now, we are researching the strong coupling in the QD-microcavity system in the cryogenic chamber. The experiment can be referred in further application of quantum dot in our system, which will be of greater use in our future implementation of quantum logic gate.更多还原