Formation of isolated artificial two-level system in solid devices

该项目的目标是实现一个使用耦合量子点的人工两能级系统，其中单电子充电效应(库仑阻塞)和零维量子能级是重要的。为了形成量子点，我们首先使用了表面栅技术，将光刻制作的表面栅沉积在GaAs/AlGaAs二维电子气晶片的顶部。在1开尔文以下的单点中观察到了库仑阻塞和零维量子能级，并观察到了双点中两个离散量子能级之间的共振隧穿，并观察到了重要的库仑阻塞效应。但是，两点系统中的相干性还有待进一步研究。在双点系统中获得了单电子电荷变化的信号，这对读出两能级系统具有重要意义。为了提高耦合量子点的工作温度，我们开发了在直径约一纳米的单壁碳纳米管中形成量子点的过程。得到了充电能量和平均能级间距，与标准电子束曝光法制作的点相比提高了一个数量级以上。最后，我们开发了一种在碳纳米管中形成耦合量子点的技术。

The aim of the project is to realize an artificial two-level system using coupled quantum dots, where the single electron charging effect (Coulomb blockade) and zero-dimensional quantum levels are important. To form the quantum dot, we first used surface gate technique, where the lithographically made surface gates are deposited on top of the GaAs/AlGaAs 2 dimensional electron gas wafer. The Coulomb blockade and zero-dimensional quantum levels have been clearly observed below 1 Kelvin in a single dots, and resonant tunneling between two discrete quantum levels in double dots have been observed with an important Coulomb blockade effect. But, coherence in the two-dot system is to be studied further. The signal of the change in single electron charge have been obtained in double-dot system, which is important for the read-out of the two level system.To increase the operation temperature of the coupled quantum dot, we have developed the process of the formation of quantum dots in single-wall carbon nanotubes which has an extremely small diameter of about one nanometer. The charging energy and the mean level spacing have been obtained which is larger by more than an order compared with the dot made by standard electron beam lithography. Finally, we have developed a technique to form coupled quantum dots in carbon nanotubes.