【作者】 薛蛟；

【导师】 朱卡的；

【作者基本信息】 上海交通大学 ， 凝聚态物理， 2008， 硕士

【摘要】 量子信息和量子计算近年来正受到越来越多的关注,而微腔量子点由于公认有希望作为未来量子信息计算单元尤其吸引了大量科学工作者的关注,产生了许多有价值的研究。但是,量子点中广泛存在退相干效应——量子态相干性的破坏,从而引发量子计算的错误和量子信息的丢失,使得量子计算器材的应用受限。而大量研究表明声子很大程度上导致了这种效应,从而理解声子如何对退相干率发生作用就显得十分宝贵。在这种量子点——微腔结构中,量子点中的激子产生了不同于通常原子的二能级系统,而这种二能级系统就是本文研究的焦点。在这一领域,已有很多人作过大量的工作,并得出了很多重要的结论。然而从前的工作没有考虑激子与微腔模差别——失谐所带来的效应。本文以幺正变换和微扰论为基础,加上对于算符作一位移对这种二能及量子点中激子的动力学进行了研究。由于存在激子与腔模的差别(失谐)前文所述的对于算符作一位移使得本来丧失的对称性得以恢复,从而计算可以顺利进行。我们得到了二能级量子点系统中的退相干率与失谐(激子频率与腔模之差)的明确解析关系。结合上面的解析式我们计算了量子点系统中的激子寿命,我们发现这种失谐对于激子寿命有着很大的影响——失谐越大,寿命越长。同时通过与最近进行的实验进行比照[Hennessy, et al., Nature 445, 896 (2007)],结果吻合得很好。另外,在有外附加光场的情况下,我们研究了系统中相干激发的激子的动力学性质。在这种情况中我们预测了在存在失谐情形中,拉比震荡依旧出现。并且失谐将很大程度上影响这种拉比震荡的模式。最后,我们讨论了激子声子相互作用α对于这种二能级系统相变的影响。更多还原

【Abstract】 Recently, quantum information and quantum computation have become very hot and are attracting more and more attention from scientists. The potential applications of semiconductor quantum dots confined in a microcavity in quantum information processing have generated considerable research efforts in recent years. Thus, the decoherence of such system, which is mainly due to the phonon effect according to recent studies limits the application of optical device. So it is indispensable to understand how the phonon contribute to the decoherence. In such dot-cavity systems, exciton in quantum dots constitutes an alternate two-level system instead of the usual two-level atomic system and this is the study focus of this paper. In this field, many studies have been conducted but few took the detuning of exciton and cavity mode into consideration. Most former studies assumed that the dot-cavity system are in resonance.This paper studies the quantum dynamics of a strongly coupled single quantum dot-cavity system with non-zero detuning in a phonon bath theoretically in terms of a perturbation treatment based on a unitary transformation and an operator displacement. The operator displacement turns the asymmetry due to the detuning and smooth the calculation. The decoherence rate due to phonons as a function of the detuning between the cavity mode and exciton is obtained analytically. It is shown that the detuning has a significant impact on the quantum-dot exciton lifetime. In the realistic experimental conditions, the calculated exciton lifetimes are in good agreement with recent experimental observation [Hennessy et al., Nature 445, 896 (2007)]. In later part of the paper, we consider the dot cavity system is coherently driven and also a non-zero detuning is introduced. In this phenomena, An excitonic Rabi Oscillation is predicted and the detuning is found to have a great impact on its mode. At last the influence of the phonon excition couplingαon phase change in such system is studied,更多还原