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Theoretical Research on Quantum Coherence in a Single Quantum Dot and coupled Quantum Dots

单量子点和耦合量子点量子相干性的理论研究

基本信息

批准号：
14540300
负责人：
TAKAGAHARA Toshihide
金额：
$ 2.11万
依托单位：
Kyoto Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540300/
关键词：
semiconductor quantum dot coherent optical phenomena Rabi oscillation quantum state control quantum coherence multi-exciton states spin relaxation

项目摘要

Near-field scanning optical microscopy revealed many important features of semiconductor nanostructures. The unprecedented high spatial resolution of NSOM was achieved recently and a strikingly new feature in the single-dot spectroscopy was reported. Namely, the spatial extent of the luminescence corresponding to the transition from the biexciton state to the exciton state is remarkably narrower than that of the exciton to the ground state transition. This observation was interpreted in terms of the center-of-mass confinement of the biexciton state, namely a kind of the dead-layer model Although this model gives a qualitative interpretation, a more quantitative theory is necessary to estimate the ratio of the FWHM of the spatial extent of both luminescence patterns and to understand the quantum-dot-size dependence of that ratio. We developed such a theory and obtained a good agreement with experiments.In recent years, a single electron in a single quantum dot or a single donor electron is extensively studied from the interest in the application to the quantum information processing. Especially, the electron spin decoherence time is one of the most important parameters which determine the performance figure of merit of the quantum information processing. We developed a theory to predict quantitatively the electron spin decoherence time and its temperature dependence and to clarify the temperature range in which the cross-over occurs between the regime dominated by the electron-phonon interaction and the regime governed by the hyperfine interaction with nuclear spinsPhoton correlation measurements were done on two photons emitted in the cascade process from a biexciton state to the ground state through an exciton state and the two photons were found not to be entangled. The origin of the absence of entanglement was pointed out to be the exciton state splitting due to the anisotropic exchange interaction in a quantum dot with anisotropic shape.

近场扫描光学显微镜揭示了半导体纳米结构的许多重要特征。近年来，NSOM获得了前所未有的高空间分辨率，并报道了单点光谱的一个引人注目的新特征。也就是说，从双激子态到激子态的跃迁所对应的发光空间范围比激子到基态跃迁所对应的发光空间范围要窄得多。这一观测结果被解释为双激子态的质心约束，即一种死层模型，尽管该模型给出了定性解释，但需要更定量的理论来估计两种发光模式空间范围的FWHM之比，并了解该比值对量子点大小的依赖关系。我们提出了这样一个理论，并与实验结果很吻合。近年来，人们对单量子点中的单电子或单给电子在量子信息处理中的应用产生了兴趣，并对其进行了广泛的研究。其中，电子自旋退相干时间是决定量子信息处理性能优劣的重要参数之一。我们开发了一种理论来定量预测电子自旋退相干时间及其温度依赖性，并澄清由电子-声子相互作用主导的状态和由核自旋超精细相互作用控制的状态之间发生交叉的温度范围。我们对双激子态通过激子态到基态的级联过程中发射的两个光子进行了光子相关测量发现不被纠缠。指出了量子点无纠缠的原因是在具有各向异性形状的量子点中，由于各向异性交换相互作用引起的激子态分裂。