Physics of Electron Spins in Quantum Dots

* 非技术摘要 * 半导体制造技术的进步使得控制电子在非常小的纳米尺寸区域内的行为成为可能。 现在已经可以控制限制在半导体小区域（称为量子点）中的电子数量。这个个人研究者奖支持的项目的总体目标是创造一个只有一个电子的量子点，并控制该电子的磁性，即“自旋”或磁矩。电子的自旋可以被认为是一个小的条形磁铁连接到电子上。就像条形磁铁一样，自旋可以指向不同的方向。 这些不同的方向代表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。 这个应用的关键是自旋保持在一个不受干扰的量子力学状态足够长的时间来进行计算。 该项目的目标是更好地表征和控制干扰自旋量子态的机制。 众所周知，由半导体砷化镓制成的量子点中的自旋改变状态太快而无法计算。 点将在硅锗中制造，其中自旋应保持在其状态更长的时间。 然后将进行实验来测量自旋保持在单个量子态的时间。 学生将接受最先进的制造和表征技术的培训。*技术摘要 * 各个研究小组已经表明，可以将单个电子限制在表面栅控横向量子点中，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依赖性。 由于磁场中的隧穿速率可以取决于电子自旋的方向，因此可以使用这些技术来测量量子点中电子的自旋状态。 该个人研究者奖支持一个项目，以测量单个电子自旋从其激发态到基态的弛豫速率作为磁场强度和方向的函数，以测试当前有关自旋弛豫机制的理论。 实验将在GaAs/AlGaAs和应变SiGe异质结构中进行，后者预计将具有较低的退相速率。 纳米电子学的可能应用包括半导体器件的更高功能，更低的功耗以及全新功能的可能性，如关联存储器和量子计算。 半导体纳米结构的研究已被证明是年轻物理学家的一个出色的训练基地。

****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.