Physics of Electron Spins in Quantum Dots

*非技术摘要*半导体制造技术的进步使控制电子在非常小的纳米尺寸区域内的行为成为可能。现在已经有可能控制限制在半导体的一个小区域内的电子的数量，这个区域被称为量子点。这一个人研究人员奖支持一个项目，其总体目标是创建一个只有一个电子的量子点，并控制该电子的“自旋”或磁矩的磁性。电子的自旋可以被认为是附着在电子上的一个小磁棒。就像条形磁铁一样，自转可以指向不同的方向。这些不同的方向代表着不同的“量子力学状态”。最近有人提出，量子点中的电子自旋可以用作量子计算机中的比特；量子计算机可以解决传统经典计算机无法解决的问题。对这一应用至关重要的是，自旋在足够长的时间内保持不受干扰的量子力学状态，以便进行计算。该项目的目标是更好地表征和控制扰乱自旋量子态的机制。众所周知，由半导体砷化镓制成的量子点中的自旋变化太快，无法计算。点将在硅锗中制造，在这种情况下，自旋应该保持更长时间。然后将进行实验，以测量自旋在单个量子态中保持多长时间。学生们将接受最先进的制造和表征技术的培训。*技术摘要*各种小组已经证明，人们可以将单个电子限制在表面栅极的横向量子点中，并且可以使用附近的导电通道来测量点上的电荷及其时间相关性。因为磁场中的隧穿速率可以依赖于电子自旋的方向，所以人们可以使用这些技术来测量量子点中电子的自旋态。这一个人研究人员奖支持一个项目，该项目测量单个电子自旋从其激发态到基态的驰豫速率作为磁场强度和方向的函数，以测试目前关于自旋驰豫机制的理论。实验将在GaAs/AlGaAs和应变SiGe异质结中进行，后者的退相率预计会更低。纳米电子学的可能应用包括半导体设备的更高功能，更低的功耗，以及联想存储器和量子计算等全新功能的可能性。半导体纳米结构的研究已被证明是年轻物理学家的杰出训练场。

****NON-TECHNICAL ABSTRACT****Advances in semiconductor fabrication technology have made it possible to control how electrons behave when confined to very small, nanometer-size, regions. It has now become possible to control the number of electrons confined in a small region of semiconductor, called a quantum dot. This individual investigator award supports a project with an overall goal of creating a quantum dot with just one electron and controlling the magnetic property know as the "spin" or magnetic moment of that electron. The spin of an electron may be thought of as a small bar magnet attached to the electron. Like a bar magnet, the spin can point in different directions. These different directions represent different "quantum mechanical states." It has recently been proposed that the electron spin in a quantum dot can be used as the bit in a quantum computer; a quantum computer could solve problems a conventional classical computer cannot. Crucial to this application is that the spin remains in an undisturbed quantum mechanical state for a long enough time to carry out a calculation. The goal of the project is to better characterize and control the mechanisms that disturb the spin quantum state. It is known that the spin in a quantum dot made of the semiconductor Gallium Arsenide changes state too quickly for computation. Dots will be made in Silicon Germanium, in which the spin should remain in its state much longer. Experiments will then be done to measure how long the spin remains in a single quantum state. Students will be trained in state-of-the-art fabrication and characterization techniques.****TECHNICAL ABSTRACT****Various groups have shown that one can confine a single electron in a surface-gated lateral quantum dot, and one can use a nearby conducting channel to measure the charge on the dot and its time dependence. Because the tunneling rate in a magnetic field can be made to depend on the orientation of the electron spin, one can use these techniques to measure the spin state of an electron in a quantum dot. This individual investigator award supports a project to measure the relaxation rate of a single electron spin from its excited state to its ground state as a function of magnetic field strength and direction to test current theories concerning spin relaxation mechanisms. Experiments will be performed in both GaAs/AlGaAs and strained SiGe heterostructures, the latter are expected to have a lower dephasing rate. Possible applications to nanoelectronics include higher functionality of semiconductor devices, lower power consumption and, the possibility of entirely new functions such as associative memory and quantum computing. Research on semiconductor nanostructures has proven to be an outstanding training ground for young physicists.