Relaxation and Coherent Control of Quantum Dots

(1)采用干涉双脉冲激发和光学声子边带时间积分探测的方法测量了应力诱导的InGaAs量子点的最低能量电子跃迁的退相。用累积光子回波的方法研究了低温下CdSe和CuBr2种量子点中受限激子的均匀线宽。均匀宽度普遍由“温度无关”项、“激子-二能级系统相互作用”项和“激子-声子限制声子相互作用”项之和给出。(2)外电场中位选择性激发的InP和InGaAs量子点的光致发光光谱和时间行为表明，声子介导的快速弛豫过程比理论预测的要快得多。这一观察证明了预测的声子瓶颈效应的崩溃。(3)高灵敏度的外差探测光子回波使我们能够观察到来自应变诱导的GaAs量子点和InP量子点的一层信号。在量子阱中形成的GaAs量子点中观察到的双激子拍频表明，与量子井中形成的量子点相比，双激子结合能额外增加。电场作用下InP量子点中的光子回波表现为隧道效应引起的退相和非指数衰减，反映了其非马尔科夫性质。(4)在电子掺杂的InP量子点中发现了三重量子拍，在量子点中观察到了4种量子拍。本研究提出了改变可调谐量子点的概念。(5)研究了电子掺杂InP量子点中的电子自旋弛豫，发现电子自旋弛豫可达到亚毫秒范围。(6)研究表明，在0.1T的磁场下，p-InAs量子点中观察到的500ps的电子自旋弛豫时间被延长到4 ns，这表明随机取向的核自旋引起的电子自旋弛豫得到了有效的抑制。

(1) Dephasing of the lowest-energy electronic transition of stress-induced InGaAs quantum dots was measured by the interferometric double pulse excitation and time-integrated detection of optical-phonon sideband in their resonant-photoluminescence spectra. Homogeneous linewidth of confined excitons in CdSe and CuBr quantum dots was investigated at low temperatures by means of accumulated photon echo. Homogeneous width is universally given by the sum of "temperature-independent" term, "exciton-two level system interaction" term and "exciton-confined acoustic phonon interaction" term.(2) Spectral and temporal behavior of photoluminescence of site-selectively excited InP and InGaAs quantum dots in external electric field showed fast phonon mediated relaxation processes is much faster than predicted theoretically. This observation demonstrates the breakdown of the predicted phonon bottleneck effect.(3) Highly sensitive heterodyne-detected photon echo enabled us to observe the signal from one layer of strain-induced GaAs quantum dots and InP quantum dots. A biexcitonic beat observed in GaAs quantum dots formed in the quantum well shows the additional increase in the biexciton binding energy compared with that of the quantum well. The photon echo in InP quantum dots under the electric field showed tunneling-induced dephasing and decayed nonexponentially, reflecting its non-Markovian nature.(4) Trionic quantum beat was discovered in eletron-doped InP quantum dots and 4 kinds of quantum beats were observed in quantum dots. The study created the concept of change tunable quantum dots.(5) Electron spin relaxation in electron-doped InP quantum dots was investigated and found to reach the submillisecond range.(6) It was shown that electron spin relaxation time of 500 ps observed in p-InAs quantum dots was elongated to 4 ns under the magnetic field of 0.1 T. This shows the efficient suppression of electron spin relaxation caused by randomly oriented nuclear spins.