固态‘人工原子’中单电荷及自旋量子态的高精度制备与探测

High-precision initialization and detection of quantum states are one of key issues for quantum information processing and high-precision physics. In this project, we are investigating the initialization and the detection of single charges and single spins with high-precision in solid- state ‘artificial atoms’, the semiconductor quantum dots. Due to the three-dimensional confinement, self-assembled semiconductor quantum dots have a discrete energy level structure, which is similar to that of the atoms, as called ‘artificial atoms’. We grow the quantum dots sandwiched in a conventional schottky diode, and investigate the photoluminescence spectroscopy of a single quantum dot as a function of bias. The carrier number in the quantum dot can be precisely controlled with identifying the neutral and charged exciton emission spectra. Using a narrow bandwidth CW laser pumping the exciton energy resonantly, single exciton photocurrent can be achieved. By analyzing the power dependent photocurrent and linewidth of photocurrent spectra, the electron/hole tunneling rates can be calculated. Under a certain bias, one carrier is left in the dot after another carrier tunneled out, resulting an initialized single charge. If the pumping laser is polarized, the spin of the initialized carrier is also determined. In addition, the pure or the entangled spin states the rest carrier can be prepared if a coherent pulsed laser is used. With such spin states, a second CW laser will be used to pumping the charged exciton state. Due the spin blockade and Pauli principle, the initialized spin quantum states can be precisely measured via the charged exciton photocurrent. The detection efficiency will be analyzed with different charged states and the decoherenc will investigated with applying magnetic fields in different orientations.

量子态的高精度的制备和测量不仅是未来量子信息的处理的可靠保障，也是精密测量物理重要基础。本项目将研究基于固态‘人工原子’，即半导体量子点，中单个电荷及其自旋的精确制备和精准测量。自组装生长的量子点由于在空间三维的局域化导致其有类似于原子结构的分立能级，因此通常被称为‘人工原子’。我们将这种量子点生长在肖特基结里面，通过电场调制的光致发光检测单量子点中的电荷数量以及不同带电激子的能级；利用圆极化光的共振激发中性激子在反向电场下的光电流光谱，研究电子和空穴的遂穿时间。当从量子点中遂穿出一个载流子时，实现了点中单电荷及自旋的初始化。采用脉冲激光的相干共振激发形成单自旋的量子叠加态，并采用另一束连续激光激发带电激子能级；由于自旋阻塞和泡利不相容原理，形成的带电激子光电流强度反映了初始化自旋量子态的几率和精度。探索不同带电激子的自旋探测效率以及磁场作用下退相干时间等。

半导体量子点是一种准零维的纳米材料，具有类似于原子的能级结构，通常被称为“人工原子”，在量子信息科学中有广泛的应用前景。单个量子点内电子和空穴的自旋具有较长的退相干时间，可作为量子比特的载体，研究单个量子点内的电子和空穴态的制备和探测具有重要意义。我们制备含有自组织生长的 InAs/GaAs 半导体量子点的 n-i-肖特基器件，通过低温下的光学和电学测量方法研究了单个量子点一系列性质。我们利用共振激发光电流的方法研究了竖直和水平磁场下的量子点中性激子能级的抗磁和塞曼分裂，并在水平磁场下观测到了暗激子态。通过非共振激发下的单量子点磁光光谱，利用竖直磁场实现了激子偶极矩的翻转，并通过异常的抗磁现象研究了零维的量子点与二维的浸润层间的耦合作用。制备了品质因子达104含有量子点的光子晶体微腔，并理论研究了基于量子点-微腔耦合系统的光子阻塞和法诺共振。并将胶体量子点与微盘耦合，增强了量子点的发光效率并有效抑制了光衰减。这些工作对以后利用量子点中激子自旋实现固态量子信息处理和量子比特的扩展有重要意义。在该项目资助下，总共发表SCI论文15篇，其中包括Nano Letters 1篇，Nano Research 1篇，ACS Photonics 1篇，Physical Review Applied 1篇，Scientific Reports 4篇，Applied physics letters 1篇，Optics Express 1篇，Semiconductor Science and Technology 1篇，SCIENCE CHINA Physics, Mechanics & Astronomy 1篇，AIP Advances1篇，激光与光电子学进展1篇，物理学报1篇。