Coherent control of exciton transitions in single semiconductor quantum dot

单半导体量子点中激子跃迁的相干控制

基本信息

批准号：
12440084
负责人：
MINAMI Fujio
金额：
$ 11.14万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

In semiconductor quantum dots, the electrons are confined three-dimensionally, and their energies become completely discrete, just as in the case of atoms. The collision probability of electrons and phonons decreases remarkably in quantum dots (phonon bottleneck). As a result, the dephasing of the polarization induced by coherent light is limited at low temperatures by the radiation process. Thus the dephasing time becomes ultralong in quantum dots, resulting in an extremely narrow homogeneous linewidth (inversely proportional to the dephasing time). We investigated the spectral width of optical transitions, especially of exciton transitions, in GaAs quantum dots. We also measured the exciton dephasing time in the quantum dots.For measurements of the spectral linewidth in single quantum dot, we used the microPL technique. Through this technique, the luminescence from a single quantum dot can be observed. The spectral width of an individual line is below the resolution (0.2 meV) of the … More measurement system. Thus it can be confirmed that the spectral width of the exciton line in the GaAs quantum dot is very narrow as predicted in the theory.To study the coherent phenomena directly in the time-domain, we applied the photon echo method to GaAs quantum dots. It can be seen that the dephasing time of the exciton is extremely long (〜1 ns) in the quantum dots. From the dephasing time, the spectral width of the exciton line in a single quantum dot can be estimated as 〜1 peV. When changing the excitation pulse power, the echo intensity is found to oscillate. It can be understood that this oscillation is analogous to the Rabi oscillation, which is observed in resonantly driven two level systems. It is therefore considered that we observed the Rabi oscillation of the exciton in the quantum dot, Because the Rabi oscillation is a fundamental phenomenon to one-qubit rotatation in quantum logic gates, it can be concluded that the quantum dot is promising as the logical circuit material of the quantum computing. Less

在半导体量子点中，电子被三维限制，并且它们的能量变得完全离散，就像原子一样，电子和声子的碰撞概率在量子点中异常降低（声子瓶颈）。相干光引起的偏振的移相在低温下受到辐射过程的限制，因此量子点中的移相时间变得超长，导致极窄的均匀线宽（成反比）。我们研究了砷化镓量子点中的光学跃迁的光谱宽度，特别是激子跃迁的光谱宽度。我们还测量了量子点中的激子移相时间。对于单个量子点中的光谱线宽的测量，我们使用了。通过这种技术，可以观察到单个量子点的发光，其光谱宽度低于 0.2 meV 的分辨率。因此可以证实GaAs量子点中激子谱线的谱宽非常窄，正如理论中预测的那样。为了直接在时域中研究相干现象，我们应用了光子回波。可以看出，量子点中激子的移相时间极长（~1 ns）。在单个量子点中，可以估计为~1peV。当改变激励脉冲功率时，发现回波强度发生振荡，可以理解，这种振荡类似于在谐振驱动的两个能级中观察到的拉比振荡。因此，我们认为我们观察到了量子点中激子的拉比振荡，因为拉比振荡是量子中单量子位旋转的基本现象。逻辑门，可以得出结论，量子点作为量子计算的逻辑电路材料是有前途的。