Lateral electron transport through single InAs quantum dots grown by molecular beam epitaxy

The transport properties of single InAs quantum dots (QDs) grown by molecular beam epitaxy have been investigated by metallic leads with nanogaps. It was found that the uncapped InAs QDs grown on the GaAs surfaces show metallic conductivities, indicating that even the exposed QDs are not depleted. On the contrary, it was found that no current flows through the exposed wetting layers. For the case of the QDs covered with GaAs capping layers, clear Coulomb gaps and Coulomb staircases have been observed at 4.2 K.     

Electronic properties of semiconductor quantum dots for Coulomb blockade applications

This paper deals with the electronic properties of Si and Ge nanocrystals (NCs) with a view to studying their potentialities for single electron devices. The 3D Poisson–Schrödinger equations are self-consistently solved for a single NC embedded in SiO₂. A 1D spherical approximation is compared to the full 3D approach. For various shapes and sizes of NC the energy levels and the density are calculated as a function of the applied voltage and the number of electrons stored in the NC. The potential properties of such nanostructures for Coulomb blockade operation are deduced.     

Simple and controlled fabrication of nanoscale gaps using double-angle evaporation

A simple and controlled method for fabricating nanometer-spaced electrodes is presented. This method uses electron-beam lithography followed by double-angle evaporation of thin metallic films. By simply changing the film thickness, one can adjust the separation of the electrodes. In this method, error is caused mainly by the granularity of the deposited metals. We have observed the Coulomb blockade effect of 20 nm Au colloidal particles captured in a gap fabricated using this method.     

基于库仑阻塞原理的多值存储器

设计了一种基于库仑阻塞原理的新型单电子多值存储器.器件包括两个多隧穿结结构和一个单电子晶体管，其中单电子晶体管起到一个静电计的作用来实现数据的读取.两个隧穿结库仑阻塞区域的大小不同使得器件具有三个稳定的存储状态.利用这个原理可以制备出多值的动态随机存储器和非挥发性的随机存储器.这种低功耗的单电子多值存储器可以实现信息的超高密度存储. 关键词： 库仑阻塞 单电子晶体管     

Spin accumulation and cotunneling effects in ferromagnetic single-electron transistors

Electron tunneling through small metallic particles (islands) coupled to two ferromagnetic electrodes is studied theoretically in the Coulomb blockade regime, where higher order tunneling processes play a significant role. Transport characteristics of the system are analyzed by the real-time diagrammatic technique. It is shown that the spin splitting of the electrochemical potential due to spin accumulation on the island should be detectable from the spacing between two resonances in the current–voltage characteristics.     

点接触平面栅型硅单电子晶体管

设计了点接触平面栅型硅单电子晶体管,利用自对准技术实现了点接触平面栅,并通过给平面栅施加偏压实现了量子点。讨论了点接触平面栅型单电子晶体管与其通道宽度和平面栅上电压的关系。对一个具有70nm宽通道的器件,先在其表面栅上施加很小的正偏压,然后又在其平面栅上施加负偏压耗尽通道,最终的研究结果显示在通道中形成了单个量子点。     

串联组装双C60 的电子结构和输运特性

利用第一原理密度泛函理论计算组装C60形成能和电子结构,用半经典隧穿理论研究了串联C60的电子输运特性。结果显示：六边形对六边形双C60比边对边双C60稳定;库仑阻塞与系统的结构密切相关,并且只有阴极结比阳极结窄时,才会出现库仑阻塞;低温时出现非常明显库仑台阶,温度较高时其被热效应抑制。     

Time-dependent bond-current functional theory for lattice Hamiltonians: Fundamental theorem and application to electron transport

The cornerstone of time-dependent (TD) density functional theory (DFT), the Runge-Gross theorem, proves a one-to-one correspondence between TD potentials and TD densities of continuum Hamiltonians. In all practical implementations, however, the basis set is discrete and the system is effectively described by a lattice Hamiltonian. We point out the difficulties of generalizing the Runge-Gross proof to the discrete case and thereby endorse the recently proposed TD bond-current functional theory (BCFT) as a viable alternative. TDBCFT is based on a one-to-one correspondence between TD Peierl’s phases and TD bond-currents of lattice systems. We apply the TDBCFT formalism to electronic transport through a simple interacting device weakly coupled to two biased non-interacting leads. We employ Kohn-Sham Peierl’s phases which are discontinuous functions of the density, a crucial property to describe Coulomb blockade. As shown by explicit time propagations, the discontinuity may prevent the biased system from ever reaching a steady state.     

Unselective ground-state blockade of Rydberg atoms for implementing quantum gates

A dynamics regime of Rydberg atoms, unselective ground-state blockade (UGSB), is proposed in the context of Rydberg antiblockade (RAB), where the evolution of two atoms is suppressed when they populate in an identical ground state. UGSB is used to implement a SWAP gate in one step without individual addressing of atoms. Aiming at circumventing common issues in RAB-based gates including atomic decay, Doppler dephasing, and fluctuations in the interatomic coupling strength, we modify the RAB condition to achieve a dynamical SWAP gate whose robustness is much greater than that of the nonadiabatic holonomic one in the conventional RAB regime. In addition, on the basis of the proposed SWAP gates, we further investigate the implementation of a three-atom Fredkin gate by combining Rydberg blockade and RAB. The present work may facilitate to implement the RAB-based gates of strongly coupled atoms in experiment.