Exciton Rabi oscillation in GaAs quantum dots

在5K条件下对GaAs量子点进行了光子回波实验。激发光源为fs钛蓝宝石激光器。激发光子能量被调谐到覆盖GaAs量子点中最低的激子。在零延迟处观察到一个优势信号，这是由于砷化镓衬底的光子回波，与量子点无关。对于较长的延迟，我们可以观察到一个缓慢衰减的信号，时间常数为~ 1ns。这种信号是由于量子点中激子相干性的消相。因此，可以得出激子在量子点中的失相时间（~ 1ns）比在普通量子阱中的失相时间（~ 1ps）要长得多。当激发脉冲功率改变时，光子回波信号强度变化较大。发现回波强度随激发功率的增加而振荡。可以理解，这种振荡类似于在共振驱动的两能级系统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。注意到在较低的激励功率下可以观察到拉比振荡。由于拉比振荡是旋转q位的必要现象，这一结果表明半导体量子点作为量子计算的逻辑电路材料是有前景的。

We performed the photon echo experiment on GaAs quantum dots at 5K. The excitation light source was a fs Ti-Sapphire laser. The excitation photon energy was tuned to cover the lowest exciton in GaAs quantum dots. A dominant signal is observed at the zero time delay, which is due to photon echoes from the GaAs substrate and is unrelated to the quantum dots. For longer delays, we can observe a slowly decaying signal with a time constant of 〜1 ns. This signal is due to the dephasing of the exciton coherence in the quantum dots. Therefore, it can be concluded that the dephasing time of the exciton is extremely long (〜1 ns) in the quantum dots as compared to that in usual quantum wells (〜1ps).When changing the exciting pulse power, the signal intensity of the photon echo varys greatly. The echo intensity is found to oscilate as the excitation power increases. 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 dots. It is noted that the Rabi oscillation can be observed under relatively low excitation power. Because the Rabi oscillation is an essential phenomenon to rotate q-bit, this result shows that the semiconductor quantum dots are promising as the logical circuit material of the quantum computing.