Electron spin transfer of single quantum dots by using teraheltz and/or laser lights

在这个项目中，我们的目标是发展在单个量子点（QD）中塞曼分裂电子态之间转移自旋的技术。然后，我们尝试了以下两种方法：太赫兹波和量子点半定域态双光子过程。结果，用后一种方法，我们成功地控制了激子自旋态，并在学术期刊上发表了详细的研究结果。在实验中，根据共线传输的延迟控制双脉冲的偏振态，我们观察到了塞曼分裂双激子态的光致发光（PL）的同相和异相振荡。在异相振荡的情况下，塞曼分裂能量的振荡以及PL的幅度被观察到。这是因为量子点中的核自旋极化是随着电子自旋极化的调制而形成的。这一结果表明量子点的半定域态可以作为λ型跃迁的中间态来控制电子和核的自旋。此外，我们还研究了量子点中电子与核自旋之间的超精细相互作用，观察到了原子核自旋极化随激发功率、极化强度和外磁场的变化的双稳态和滞后响应.利用这种核自旋开关，我们证明了量子点电子的有效g因子可以从负到正进行宽范围的调谐，并被设置为零。

In this project, we aimed the development of the technique to transfer the spin between the Zeeman-split electron states in a single quantum dot (QD). Then, we tried the following two methods; use of teraheltz wave and two-photon process via half-localized state in a QD. As a consequence, by the latter method, we succeeded the control of the exciton spin state and the details were published in the academic journals. In the experiments, depending on the light polarizations of the co-linearly propagating delay-controlled double pulses, we observed the in-phase and out-of-phase oscillations of photoluminescence (PL) from the Zeeman-split two exciton states. In the case of the out-of-phase oscillations, the oscillation of the Zeeman splitting energy as well as the magnitude of the PLs was observed. This is because the nuclear spin polarization in a QD was formed and followed the modulation of the electron spin polarization. This result indicates that the half-localized state of QDs is available as the intermediate state in the Lambda-type transition in order to control of the electron and nuclear spins. In addition, we investigated the hyperfine interaction between electron and nuclear spins in a single QD, and the bistability and hysteretic response of the nuclear spin polarization were observed in the dependence on excitation power, polarization, and external magnetic field. By using this nuclear spin switching, we proved that the effective g factor of the QD electron could be tuned widely from negative to positive and be set to zero.