Coherent control of exciton transitions in single semiconductor quantum dot

在半导体量子点中，电子被三维限制，它们的能量变得完全离散，就像原子一样。在量子点中，电子与声子的碰撞几率显著降低（声子瓶颈）。因此，相干光引起的偏振的退相在低温下受到辐射过程的限制。因此，退相时间在量子点中变得超长，导致极窄的均匀线宽（与退相时间成反比）。我们研究了GaAs量子点中光跃迁，特别是激子跃迁的光谱宽度。我们还测量了量子点中激子的退相时间。对于单个量子点的光谱线宽的测量，我们采用了微光致发光技术。通过这种技术，可以观察到来自单个量子点的发光。单个谱线的谱宽低于光谱仪的分辨率（0.2 meV）。 ...更多信息 测量系统为了直接在时域内研究量子点中的相干现象，我们将光子回波方法应用于GaAs量子点中。可以看出，激子的退相时间在量子点中非常长（101 ns）。从退相时间，在一个单一的量子点的激子线的光谱宽度可以估计为101 peV。当改变激励脉冲功率时，回波强度出现振荡。可以理解，这种振荡类似于拉比振荡，拉比振荡在共振驱动的两能级系统中观察到。由于量子点中激子的拉比振荡是量子逻辑门中单量子比特量子化的基本现象，因此量子点作为量子计算的逻辑电路材料是很有希望的。少

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