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。 NSOM的前所未有的高空间分辨率最近实现了，并且在单点光谱法中有了引人注目的新功能。也就是说，相对于从Biexciton状态到激子状态的过渡相比，发光的空间范围比激子向基态过渡的过渡要窄。该观察结果是用Biexciton状态的质量中心限制来解释的，即一种死层模型，尽管该模型给出了定性的解释，但对于估计FWHM的比率是更定量的理论，是必要的。两种发光模式的空间范围，并了解该比率的量子尺寸依赖性。我们开发了这样的理论，并与实验达成了良好的一致性。近年来，从单个量子点或单个供体电子中的单个电子从对量子信息处理的应用中的兴趣进行了广泛的研究。特别是，电子自旋分解时间是确定量子信息处理功绩的最重要参数之一。我们开发了一种理论，可以定量预测电子自旋分解时间及其温度依赖性，并阐明在由电子 - phonon相互作用支配的政权和由核替代性相互作用控制的状态下发生的跨界的温度范围。在从Biexciton状态到基态的两个光子在通过激子状态发出的两个光子上进行了相关测量，发现两个光子没有被纠缠。指出，由于具有各向异性形状的量子点的各向异性交换相互作用，因此缺乏纠缠的起源是激子状态分裂。