The Effective Conduction Band Edge Method of Quantum Correction to the Monte Carlo Device Simulation

To include quantum effects, a quantum correction is made to the semi-classical Monte Carlo (MC) simulation by the effective conduction band edge (ECBE) method. The quantum corrected potential energy can be calculated from the classical potential energy by the ECBE equation and thus the quantum mechanical force in the simulation replaces the classical force. Under the non-equilibrium condition, carriers have a temperature different from the lattice. For the simulation of a double-gate MOSFET, we replace thermal energy in the ECBE equation with the average value of the stress tensor along each transverse line, to account for the variation of the electron “temperature” along the longitudinal direction. A 3 nm thick double gate nMOSFET is simulated. The result shows that electrons now see a higher barrier from the source to the drain if the carrier temperature is considered, resulting in a smaller drain current compared to that obtained from the previous ECBE method.     

Quantum Lattice-Gas Automata Simulation of Electronic Wave Propagation in Nanostructures

We report the two- and three-dimensional quantum lattice-gas automata simulation for one-particle electronic wave propagation in nanostructures. The transmission coefficient of the electronic wave through the two-dimensional quantum point contact is investigated taking account of the surface roughness of the confinement wall. It is demonstrated that the electron transmission is significantly affected by the surface roughness pattern even if the same roughness parameter is assumed. We also perform the three-dimensional simulation, and the wave propagation in the structure like an ultrathin-body MOSFET is visualized.     

Quantum Control of Capture Processes into Localized States of a Quantum Dot

The capture of an electronic wave packet moving in a quantum wire into localized states of a quantum dot by means of LO phonon emission is studied on a quantum kinetic level. In general, if there is more than one bound state the capture process leads to the creation of a superposition of these states resulting in an oscillating wave packet inside the dot. It is shown that these oscillations can be efficiently controlled by means of the capture of a second wave packet moving towards the dot from the other side. Depending on the phase of the oscillations at the time of arrival of the second wave packet the amplitude of the spatial oscillations is either reduced or enhanced.     

On dissipative two‐state quantum cells and cellular networks

Quantum cellular networks are structures composed of two‐state quantum cells in equilibrium with a stationary thermal bath, which interact among themselves in a classical way. It is shown that if system–bath coupling is set up in the representation based on the given states, as done in the literature, or in the energy representation, as the theory assumes under several approximations, different models are obtained for the cell performance, and hence for the dynamics of the whole network. The model based on the state representation could also be derived by a heuristic approach. The final choice should be decided by experiment. Copyright © 2004 John Wiley & Sons, Ltd.     

Effective Mass Approach for n-MOSFETs on Arbitrarily Oriented Wafers

The general theory for quantum simulation of cubic semiconductor n-MOSFETs is presented within the effective mass equation approach. The full three-dimensional transport problem is described in terms of coupled transverse subband modes which arise due to quantum confinement along the body thickness direction. Couplings among the subbands are generated for two reasons: due to spatial variations of the confinement potential along the transport direction, and due to non-alignment of the device coordinate system with the principal axes of the constant energy conduction band ellipsoids. The problem simplifies considerably if the electrostatic potential is separable along transport and confinement directions, and further if the potential variations along the transport direction are slow enough to prevent dipolar coupling (Zener tunneling) between subbands. In this limit, the transport problem can be solved by employing two unitary operators to transform an arbitrarily oriented constant energy ellipsoid into a regular ellipsoid with principal axes along the transport, width and confinement directions of the device.     

Proximity Effect of the Contacts on Electron Transport in Mesoscopic Devices

The Wigner function formalism is used for studying electron quantum transport in mesoscopic systems. In this work we show that, if the correlation of the electron wave function vanishes outside the region of interest (for example inside the contacts), then transport is affected inside the device. This property is verified analytically. Results show that, for very short devices, tunneling is actually influenced by the distance between the contacts. Modification in the electron density and conductivity have been numerically observed.     

基于测量的量子图像识别研究

目前,已有的量子相似度比较算法:1)逐个比较图像对应位置的像素值;2)将两幅图像分别用量子态表示,再将两幅图像进行连接(意味着将两个量子态连接成一个态),再进行相关的量子操作。所提出的比较算法,是在不连接图像的基础上,将图像用量子态表示,进行控制交换(c-Swap)操作,再进行量子测量,根据测量结果判断两幅图像的相似度。将所提的量子相似度比较算法应用到量子手势识别中,实验结果表明所提算法在识别问题上具有可行性。在经典领域中,手势识别的流程比较复杂。而在量子领域中,无需提取手势的颜色、纹理、特征等步骤,直接可以将手势进行二值化表示,再根据所提的图像相似度算法来实现手势识别。     

Numerical Calculation of Electronic Structure for Three-Dimensional Nanoscale Semiconductor Quantum Dots and Rings

In this paper the electronic structure of nanoscale ellipsoid-torus-shaped semiconductor quantum dot and quantum ring is investigated of utilizing a unified model. This three-dimensional model considers the effective one-band Hamiltonian, the position- and energy-dependent effective mass approximation and Landé factor, the finite hard wall confinement potential, and the Ben Daniel-Duke boundary conditions. It is solved numerically without any fitting parameters by using a computationally cost effective nonlinear iterative method. It is found that the penetration of magnetic fields into non-simply connected topology of structures leads to substantial difference in the transition energy between InAs/GaAs quantum dot and quantum ring. The quantum ring exhibits non-periodical electron-hole transition energies when the magnetic field increases. Contrary to the one-dimensional periodical argument on the ring's energy spectra, our examination into the nanoscale semiconductor quantum ring agrees with the experimental result. The energy band gap of quantum dot is an increasing function of the magnetic field. For quantum rings the energy band gap oscillates non-periodically and the oscillation period is strongly controlled by the inner radius of structures. The magnetization of quantum ring not only jumps non-periodically but also saturates eventually when the magnetic field increases.     

Overview of progress in quantum systems control

The development of the theory on quantum systems control in the last 20 years is reviewed in detail. The research on the controllability of quantum systems is first introduced, then the study on the quantum open-loop control methods often used for controlling simple quantum systems is analyzed briefly. The learning control method and the feedback control method are mainly discussed for they are two important methods in quantum systems control and their advantages and disadvantages are presented. According to the trends in quantum systems control development, the paper predicts the future trends of its development and applications. A complete design procedure necessary for the quantum control system is presented. Finally, several vital problems hindering the advancement of quantum control are pointed out. Translated from Chinese Journal of Quantum Electronics, 2003, 20(1): 1–9 [译自:: 量子电子学报]     

Quantum dot blinking: relevance to physical limits for nanoscale optoelectronic device

In designing nanoscale optoelectronic devices based on a small number of active quantum dots, it is of interest to consider that semiconductor nanocrystals (quantum dots) are observed to blink “on” and “off”. The time probability distributions scale as an inverse power law for colloidal quantum dots and exponentially for self-assembled dots. Possible mechanisms that cause the inverse power law and exponential blinking statistics are discussed in the paper and the relevance to quantum-dot based system architectures is discussed.     

Influence of temperature and optical confinement on threshold current of an InGaAs/InP quantum wire laser

In this paper, we investigate the influence of the temperature on gain and threshold current density of a V-groove quantum wire InGaAs/InP laser. The calculation shows that room-temperature operation can be achieved if the optical confinement is large enough (0.26% in our case), while its slight improvement above this limit (around 0.4%) can provide a significant reduction of the threshold current (more than 70%) and an improved temperature stability of the laser.     

Quantum drift-diffusion model for IMPATT devices

Quantum correction is necessary on the classical drift-diffusion (CLDD) model to predict the accurate behavior of high frequency performance of ATT devices at frequencies greater than 200 GHz when the active layer of the device shrinks in the range of 150–350 nm. In the present work, a quantum drift-diffusion model for impact avalanche transit time (IMPATT) devices has been developed by incorporating appropriate quantum mechanical corrections based on density-gradient theory which macroscopically takes into account important quantum mechanical effects such as quantum confinement, quantum tunneling, etc. into the CLDD model. Quantum potentials (synonymous as Bohm potentials) have been incorporated in the current density equations as necessary quantum mechanical corrections for the analysis of millimeter-wave (mm-wave) and Terahertz (THz) IMPATT devices. It is observed that the large-signal (L-S) performance of the device is degraded due to the incorporation of quantum corrections into the model when the frequency of operation increases above 200 GHz; while the effect of quantum corrections are negligible for the devices operating at lower mm-wave frequencies.     

High‐responsivity AlGaN–GaN multi‐quantum well UV photodetector

In this paper, we propose a set of AlGaN–GaN multi‐quantum well (MQW) photodetectors based on p‐i‐n heterostructures with 14 AlGaN–GaN MQW structures in i‐region, where GaN quantum well has 6 nm thickness and Al_xGa_1−xN barrier thickness is 3 nm. In this structure, the peak responsivity of 0.19 A/W at 246 nm is reported. In addition, we investigate effects of various parameters on responsivity, and we show that responsivity of MQW‐based photodetectors strongly depends on proper device design, that is, number of quantum wells, well thickness, barrier thickness, and mole fraction. We also show that increasing number of quantum wells, thickness of wells, and mole fraction as well as decreasing thickness of barriers, increase the responsivity. Using obtained results, we proposed optimal structure. Copyright © 2013 John Wiley & Sons, Ltd.     

Adaptive Measurements in the Optical Quantum Information Laboratory

Adaptive techniques make practical many quantum measurements that would otherwise be beyond current laboratory capabilities. For example, they allow discrimination of nonorthogonal states with a probability of error equal to the Helstrom bound, measurement of the phase of a quantum oscillator with accuracy approaching (or in some cases attaining) the Heisenberg limit (HL), and estimation of phase in interferometry with a variance scaling at the HL, using only single qubit measurement and control. Each of these examples has close links with quantum information, in particular, experimental optical quantum information: the first is a basic quantum communication protocol; the second has potential application in linear optical quantum computing; the third uses an adaptive protocol inspired by the quantum phase estimation algorithm. We discuss each of these examples and their implementation in the laboratory, but concentrate upon the last, which was published most recently [Higgins et al. , Nature, vol. 450, p. 393, 2007].      

Quantized conductance without reservoirs: Method of the nonequilibrium statistical operator

We introduce a generalized non-equilibrium statistical operator (NSO) to study a current-carrying system. The NSO is used to derive a set of quantum kinetic equations based on quantum mechanical balance equations. The quantum kinetic equations are solved self-consistently together with Poisson’s equation to solve a general transport problem. We show that these kinetic equations can be used to rederive the Landauer formula for the conductance of a quantum point contact, without any reference to reservoirs at different chemical potentials. Instead, energy dissipation is taken into account explicitly through the electron-phonon interaction. We find that both elastic and inelastic scattering are necessary to obtain the Landauer conductance.     

A new approach for numerical simulation of quantum transport in double-gate SOI

Numerical simulation of nanoscale double-gate SOI (Silicon-on-Insulator) greatly depends on the accurate representation of quantum mechanical effects. These effects include, mainly, the quantum confinement of carriers by gate-oxides in the direction normal to the interfaces, and the quantum transport of carriers along the channel. In a previous work, the use of transfer matrix method (TMM) was proposed for the simulation of the first effect. In this work, TMM is proposed to be used for the solution of Schrodinger equation with open boundary conditions to simulate the second quantum-mechanical effect. Transport properties such as transmission probability, carrier concentration, and I–V characteristics resulting from quantum transport simulation using TMM are compared with that using the traditional tight-binding model (TBM). Comparison showed that, when the same mesh size is used in both methods, TMM gives more accurate results than TBM. Copyright © 2007 John Wiley & Sons, Ltd.     

基于量子遗传算法优化的无线电能传输模型

传统方法设计电磁谐振式无线电能传输系统时,参数一直靠人工设定,实际应用中很难达到最优的传输效率。文章使用量子遗传算法对无线电能传输模型的参数进行优化,该算法以量子理论和量子计算为基础,采用量子比特实现个体编码,然后对每次迭代中的个体通过量子旋转门操作进行最优解搜索;最后,通过对一个谐振式无线电能传输系统进行仿真分析,对算法的有效性进行了验证;事实证明,该算法能够较快地搜索到局部最优解,验证了量子遗传算法对参数优化问题的有效性,为无线电能传输模型的制作优化奠定基础。     

氧化物薄膜抑制量子点的光衰性能

量子点应用于LED中,可获得高饱和性、宽色域光源,在液晶显示背光源领域前景广阔。但是,影响量子点寿命的因素很多,如温度、水氧等,严重阻碍了其推广应用。目前,水氧对量子点光衰性能影响的研究较少,本文旨在研究无机氧化物薄膜阻隔层对量子点光衰性能的影响。量子点成膜后表面溅射Al2O3、SiO2水氧隔离薄膜,蓝光LED激发绿光量子点,研究其光衰性能。结果表明,与无隔离膜的样品相比,单层SiO2薄膜的样品光衰性能有所改善;双层的SiO2薄膜及SiO2/Al2O3复合薄膜,可以有效地减小薄膜孔洞大小和孔洞密度,阻隔水氧的进入,抑制量子点的光衰减,提高量子点寿命。     

Effects of substrate orientation on opto-electronic properties in self-assembled InAs/GaAs quantum dots

Electronic structure and optical transition characteristics in (100), (110), and (111) oriented InAs/GaAs quantum dots (containing \({\sim }2\) million atoms) were studied using a combination of valence force-field molecular mechanics and 20-band \(sp^{3}d^{5}s^{*}\) atomistic tight-binding framework. These quantum dots are promising candidates for non-traditional applications such as spintronics, quantum cryptography and quantum computation, but suffer from the deleterious effects of various internal fields. Here, the dependence of strain and polarization fields on the substrate orientation is reported and discussed. It is found that, compared to the (100) and (110) oriented counterparts, quantum dots grown on the (111) oriented substrate exhibit a smaller splitting (non-degeneracy) in the excited \(P\) states and enhanced isotropy in the interband optical emission characteristics.