【作者】 吴晓伟；

【导师】 韩正甫； 郭光灿；

【作者基本信息】 中国科学技术大学 ， 光学， 2010， 博士

【摘要】 量子信息学是近年来受到广泛关注的新兴学科,它汇集了基础物理学中量子力学的研究和信息技术的演进发展,不仅开拓了经典信息技术领域,也对量子力学的探索产生了重要的推动作用。量子计算作为量子信息中的研究方向之一,能够通过量子力学的基本原理解决经典计算机无法或难以解决的算法问题,将会产生深远的影响。为了能够在物理体系上实现有效的量子态的操控,实现量子计算,众多的结构方案被提出,其中基于腔量子电动力学的思路,由于可以提供一个近乎理想的进行量子态操控的平台,而且适合小型化和集成化,因而具有很好的发展前景。基于这个动因,本文以量子计算的物理实现为目标,围绕腔量子电动力学,展开一系列相关的工作。现代微细加工技术的发展,以及材料制备手段的进步,为腔量子电动力学同时提供了所需要的两方面要素。前者促生了具有微小尺度的介质微腔,而其中基于回音壁模式的光学微腔因为其极高的品质因数和很小的模式体积,最具有吸引力。后者则导致了量子点这种人造原子体系的出现,其参数的可控性及优良的物理特征使之在应用上广受关注。为了以回音壁模式光学微腔和量子点构成探索腔量子电动力学效应的平台,我们分别在以上两个分支方向开展研究,并结合两者,探索了腔量子电动力学的相关效应。本文就主要介绍了在上述方面所取得的成果。在回音壁模式光学微腔方面,我们通过自行发展的一套相关设备和制备方法,制作出了基于硅基芯片的微盘型光学微腔,并且能通过后续的处理手段,形成具有独特结构的微芯圆环光学微腔,达到了很高的品质因数和很小的模式体积。这两种类型的平面结构的光学微腔,可以产生很强的Purcell效应,为腔量子电动力学的进一步实验研究提供了高品质的载体。另一方面,我们发现回音壁模式的光学微腔自身也存在着很多新颖的物理现象,由于其特别的性能,很多原先非常微弱的现象会在这种微腔中得到显著增强,比如材料产生的Rayleigh散射。由此我们深入探索了散射导致的模式耦合现象,并且直接通过实验手段获得了腔内模式耦合强度。通过对微腔自身的研究,也加深了对微腔与量子点耦合体系的认识。单就量子点而言,它已经包含了丰富的内容值得加以研究,而为了实现量子点在腔量子电动力学中的应用,单个量子点的发光过程更值得关注。因此,在我们的工作中,分别对量子点的单光子发射、量子点的荧光衰减过程、量子点荧光的某些特殊效应、以及用以直接调制量子点发光过程的方法,进行了相关的实验研究。获得的结果对于进一步在我们的实验中应用量子点提供了参考。我们将回音壁模式光学微腔和量子点相结合,构成了研究二能级结构与光场相互耦合的体系。在实验上观察到微腔对于量子点发光可以产生直接的影响,通过Purcell效应,能够导致量子点的荧光光谱受到明显调制。同时我们借助近场耦合器件,还实现了微腔对量子点的可控耦合,相关的实验技术也为实现微腔对单个量子点的可控的Purcell效应创造了条件。文中所介绍的我们所开展的实验工作,已经证明回音壁模式光学微腔和量子点耦合的体系在腔量子电动力学的实验中具有发展潜力,他们独特的性质既可以单独发展,用于相关工程应用性领域和基础研究领域,更能有效的推进量子信息研究的进步,并且有望为量子计算器件的实现打下基础。更多还原

【Abstract】 Quantum information is new branch of science, which has received widely concern in recent years. It combines the research quantum mechanics in basic physics and development from information technique, and this subject not only expands the classical information technique field, but also promotes the exploration of quantum mechanics. Quantum computation is one of the research fields in quantum information. Upon the basic theories of quantum mechanics, quantum computation has the ability to solve the problems which are not able or hard to compute by classical computer, and that could lead to profound influence. In order to realize quantum computation and achieve effective control of quantum state in a physical system, many schemes have been proposed. Among those schemes, the cavity quantum electrodynamics (QED) has promising prospect, since it can provide an almost ideal platform to control the quantum state, and is suitable for miniaturization and integration. Basing on that reason, this thesis targets on the physical realization of quantum computation, and performs a series of works centered on the cavity QED.Developments of modern microfabrication technology and progress in material preparation have provided both parts of what is need in cavity QED. The former brought the dielectric microcavities with small dimension, and the whispering gallery mode microcavity is of great attraction, because it keeps high quality factor and small mode volume. Meanwhile, the latter has lead to generation of quantum dots which is an artificial atom, it is controllable in fabrication and has superior character. For the purpose of constructing the system within microcavity and quantum dot to study the cavity QED effects, those two branches are investigated respectively, and by combining them, some cavity QED effects have been researched. In this article, we are going to introduce the achievements in aforementioned fields.Towards the whispering gallery mode microcavity, we have developed a set of related equipments and fabrication method to fabricate silicon chip based microdisk cavity. Furthermore, by using subsequent procedure the microtoroid cavity with unique structure can be formed. That cavity has reached high quality factor and small mode volume, which are related to strong Purcell effect. The planar optical microcavity is able to generate strong Purcell effect that brings the great support for cavity QED experiment. In another aspect, we found that many new phenomena exist in the whispering gallery mode microcavity, due to its special characters some effects which originally are very weak has been enhanced, such as Rayleigh scattering from material. As the result, we explored the scattering induced modal coupling, in microcavities and directly derived modal coupling strength by experimental way. Through the study on microcavity, the knowledge of coupling between microcavity and quantum dot has been gained.So far as the development of quantum dot, large quantities of content are worth studying. However, the luminescent process in single quantum dot is more attractive towards application in cavity QED. Therefore, we have studied the following aspects, which are the single photon emitting, luminescence decay process, some special character of quantum dot’s fluorescence and the way for directly tuning photon emitting from quantum dot. The experiment results can be referred and applied in further application of quantum dot in our experiments.Within whispering gallery mode microcavity and quantum dot, we composed the coupled system which has two level energy structure and optical field. In experiment, the microcavity can directly influence quantum dots emission via Purcell effect. The modulated luminescent spectrum has been observed. In the mean time, we also realized controlled coupling between microcavity and quantum dots with the help of near field coupling device. Related experiment technology provides the conditions to achieve a controllable Purcell effect within the microcavity and single quantum dot.Our experiment works introduced in this thesis have already proved the potential of whispering gallery mode microcavity coupling with quantum dot to study the cavity QED. The superior characters of those elements guarantee that they can be applied in engineering and basic research field. More importantly, they can make advancement for study of quantum information, and are hopeful to construct solid foundation for quantum computation device.更多还原