GaAs半导体量子箱中电子的斯塔克效应

在有效质量近似下,利用变分法研究了在GaAs半导体量子箱中电子能量的斯塔克效应.结论表明：电场平行于量子箱的中心轴时,斯塔克能移只与量子箱高度有关;电场垂直于中心轴时,斯塔克能移仅仅与它的截面尺寸有关.当电场方向与中心轴夹角为任意角时,斯塔克能移与高度和截面都有关.同时在低场和高场极限下,理论上分析了电场大小和量箱尺寸对斯塔克能移的影响.     

GaAs半导体量子箱中电子的斯塔克效应

在有效质量近似下,利用变分法研究了在GaAs半导体量子箱中电子能量的斯塔克效应.结论表明:电场平行于量子箱的中心轴时,斯塔克能移只与量子箱高度有关;电场垂直于中心轴时,斯塔克能移仅仅与它的截面尺寸有关.当电场方向与中心轴夹角为任意角时,斯塔克能移与高度和截面都有关.同时在低场和高场极限下,理论上分析了电场大小和量箱尺寸对斯塔克能移的影响.     

石墨烯纳米带量子点中的量子混沌现象

在20 mK的极低温下测量了石墨烯纳米带量子点的电子输运性质,观测到清晰的库仑阻塞菱形块和对应量子点激发态的电导峰.对库仑阻塞近邻电导峰间距和峰值进行了统计分析,发现其统计分布分别满足无规矩阵理论描述的Wigner-Dyson分布和Porter-Thomas分布,说明石墨烯纳米带量子点在低温下出现了量子混沌现象.还讨论了这种长方形量子点中量子混沌的可能成因. 关键词： 石墨烯纳米带 量子点 库仑阻塞 量子混沌     

太赫兹电磁场照射下量子线中的纳米电子力

研究两端连接电子库的量子线在太赫兹(THz)电磁场横向辐射下的电子力学问题. 在自由电子近似下求得了弹道区二能级电子波函数解析表达式,发现电子概率在两个能态间随线轴坐标作Rabi振荡, 其幅度与外场强度和频率有关. 利用热力学统计算符方法并利用波函数计算出了传导电子对量子线中张力贡献的大小. 其计算结果可表示成与外场无关和与外场有关的两部分之和,前者与已有的实验观测和理论计算结果一致, 而与外场参量有关的部分可用量子相干理论解释. 关键词： 量子线 THz电磁场 纳米电子力     

一类弯曲量子线的量子束缚态

对电子在弯曲量子线中的弹道输运性质进行了理论研究.弯曲量子线由T型量子线和单曲量子线组成.该有限长的量子结构分别与两半无限长的量子通道相连,当施加一偏压时,量子通道分别可作为电子的发射极和收集极.计算结果表明,当入射电子的能量小于量子结构横向上的第一个本征模时,电导存在两个峰.进一步指出,这些峰来自于电子共振隧穿量子结构中的量子束缚态.并详尽地讨论了这些量子束缚态的性质. 关键词： 量子束缚态 共振隧穿 电导 量子线     

热Fock态下量子效应对介观左手传输线负折射系数的影响

基于热场动力学理论研究了热Fock态下量子效应对介观左手传输线微波段负折射系数的影响.结果表明:负折射系数随电流涨落的增加表现出线性递增的特点,而随温度的升高、频率的增大表现出锐减特性;负折射系数的变化幅度受光子数调控.该结论可对基于左手传输线开发的微波器件的微型化、集成化研究提供参考.     

量子环中量子比特的声子效应

在量子环中电子与体纵光学声子强耦合的情况下,通过求解能量本征方程,得出了电子的基态和第一激发态的本征能量及其波函数,进而以电子-声子系的基态与第一激发态构造了一个量子比特.数值计算结果表明量子比特内电子的空间概率密度分布随时间和空间角坐标作周期性振荡,且振荡周期随耦合强度的增大而减小,说明声子将导致量子比特相干性降低;还表明振荡周期随量子环内径（或外径）的增大而增大,因此适当改变量子环的尺度,可以提高量子比特的相干性. 关键词： 量子环 量子信息 量子比特     

囚禁离子非线性Jaynes-Cummings模型量子场熵演化特性

利用VonNeuuman量子约化熵理论研究了驻波激光场与囚禁在谐振势中的离子单量子共振相互作用系统中量子场熵的时间演化特性,通过数值计算详细讨论了Lamb-Dick参数、离子质心在驻波激光场中的位置以及囚禁离子初始状态对量子场熵演化特性的影响.结果表明:Lamb-Dick参数影响囚禁离子与驻波激光场之间量子纠缠的频率和幅度,其值越大离子与光场之间的平均纠缠程度越低;随着离子质心从驻波激光场的波节向波腹移动,二者之间量子纠缠的振荡频率逐渐变慢,纠缠强度逐渐减弱;随着囚禁离子处于激发态概率的减小,离子与光场之间的量子纠缠呈现先增强后减弱的变化趋势.这些特性对于纠缠态的制备以及利用囚禁离子进行量子通讯等信息处理过程有一定的参考价值.     

基于量子点接触的开放双量子点系统电子转移特性

基于量子点接触探测器(QPC)理论上研究了双量子点(DQD)系统在耗散环境和纯退相环境影响下的电子转移特性.结果表明,耗散环境中探测器导致的退相干会增大平均电流和Fano factor随时间演化的值,并观察到量子芝诺效应的存在.在对称的DQD情况下,弛豫减小了平均电流随时间演化的震荡振幅.在非对称的DQD情况下,弛豫降低了Fano factor随时间演化的峰值.纯退相环境中测量会阻碍共隧穿过程中不同电流通道之间的转换,导致Fano factor的极高值.在对称的DQD情况下,增大纯退相速率会提高Fano factor.在非对称的DQD情况下,动力学随时间的演化对纯退相环境不敏感.另外,还发现探测器内n个电子的转移几率只受QPC与DQD耦合的影响.我们的结论可以为实验工作者研究电子输运特性提供理论参考.     

介观RLC电路在热真空态下的量子涨落

利用热场动力学的方法研究了介观RLC电路在具有热噪声的真空态下电荷和磁通(电流)的量子涨落.从而得到了有限温度下这一电路在热真空态下的量子涨落与温度的关系.结果表明,介观RLC电路的量子涨落不仅与电路中的元件参量和电路的共振频率ω有关,而且与温度T有关.温度越高,介观RLC电路的量子噪声越大 关键词： 介观RLC电路 热真空态 量子涨落     

Observation of the Fano-Kondo antiresonance in a quantum wire with a side-coupled quantum dot

We have observed the Fano-Kondo antiresonance in a quantum wire with a side-coupled quantum dot. In a weak coupling regime, dips due to the Fano effect appeared. As the coupling strength increased, conductance in the regions between the dips decreased alternately. From the temperature dependence and the response to the magnetic field, we conclude that the conductance reduction is due to the Fano-Kondo antiresonance. At a Kondo valley with the Fano parameter q approximately 0, the phase shift is locked to pi/2 against the gate voltage when the system is close to the unitary limit in agreement with theoretical predictions by Gerland et al. [Phys. Rev. Lett. 84, 3710 (2000)].     

Characteristics of quantum conductance in a quasi-one-dimension quantum wire containing cavity structures

Quantum-mechanical calculations of the conductance for model devices, consisting of dual semi-infinite quantum wires connected in series by a cavity, are carried out with use of the coupled-mode transfer method and mode matching technique. The effects of the mode-mode coupling and geometry-induced scattering on the quantum conductance are in detail studied by varying the geometric structure of the cavity. There are no traces of quantization conductance. The pattern of the conductance displays many peaks and dips. The threshold energy of the first onset of the conductance is lower than the normal value for opening the propagation channel of the lowest subband in the quantum wire. The overall character of the conductance exhibits heavy fluctuations around the classical conductance for the relevant point contact. The fluctuation amplitude is of order of 2e ²/h, similar to universal conductance fluctuations. The oscillatory structure becomes rich and dense as the scale of the cavity increases. There is a global trend for the conductance to rise as the cavity is compressed. The structures of resonant peaks and antiresonance dips in the conductance are originated from the mode coupling among the subbands in the cavity and quantum wires. The heavy conductance fluctuation may be caused by the quantum interference of the electron waves due to the multiple scattering (reflections) of electrons by the cavity boundaries.     

Heat transport in a four-perpendicularity-bend quantum waveguide

Using the scattering matrix method, we investigate acoustic phonon transmission and thermal conductance in a four-perpendicularity-bend quantum waveguide at low temperatures. The transmission spectrum of the quantum waveguide displays a series of resonant peaks and dips; and when one of the bend heights is larger than or equal to the minimum of the dimensions of the phonon channel in the quantum waveguide, a stop-frequency gap will appear; and some single four-perpendicularity-bend quantum waveguides with larger bend heights exhibit narrower width or smaller number of the stop-frequency gaps than that with smaller bend heights. The thermal conductivity is much sensitive to the change of the smaller heights and longitudinal lengths of the bend section; and the thermal conductivity decreases with the increasing of the temperature first, then increases after it reaches a minimum. The investigations of multiple four-perpendicularity-bend waveguides connected in series indicate that the first additional waveguide suppresses the transmission coefficient and forms the stop-frequency gap; and two additional resonance peaks will be formed when each four-perpendicularity-bend waveguide is added in the series. The results could be useful for controlling thermal conductance artificially and the design of phonon devices.     

I–V characteristic of electronic transport through a quantum dot chain: The role of antiresonance

The I–V spectrum of electronic transport through a quantum dot chain is calculated by means of the nonequilibrium Green function technique. In such a system, two arbitrary quantum dots are connected with two electron reservoirs through leads. When the dot-lead coupling is very weak, a series of discrete resonant peaks in electron transmission function cause staircase-like I–V characteristic. On the contrary, in the relatively strong dot-lead coupling regime, stairs in the I–V spectrum due to resonance vanish. However, when there are some dangling quantum dots in the chain outside two leads, the antiresonance which corresponds to the zero points of electron transmission function brings about novel staircase characteristic in the I–V spectrum. Moreover, two features in the I–V spectrum arising from the antiresonance are pointed out, which are significant for possible device applications. One is the multiple negative differential conductance regions, and another is regarding to create a highly spin-polarized current through the quantum dot chain by the interplay of the resonance and antiresonance. Finally, we focus on the role that the many-body effect plays on the antiresonance. Our result is that the antiresonance remains when the electron interaction is considered to the second order approximation.     

Giant antiresonance in electromagnetic wave reflection from a 3D structure with ferrite spinel nanoparticles

We analyze the microwave properties of nanocomposite materials obtained by embedding opal matrices (regular packing of SiO₂ spheres about 250 nm in diameter) of ferrite spinel nanoparticles in the interspherical space. It is found that the main reason for microwave changes is the magnetic resonance in a nanocomposite. In addition to the resonance, antiresonance also takes place, which is manifested as a minimum of absorbed power at frequencies higher than a certain frequency characteristic of the given type of ferrite particles. Antiresonance appears in the fields smaller than the resonance field. The amplitude of the reflected signal in antiresonance increases fourfold. The measurements are taken in the frequency range from 26 to 38 GHz. The change in the moduli of transmission and reflection coefficients in the external magnetic field in a rectangular waveguide containing a nanocomposite is analyzed. The modulus of the wave transmittance through a rectangular resonator with a nanocomposite specimen is measured. The structural analysis of nanocomposites is carried out. In addition, the magnetization curves and hysteresis loops are measured.     

Resonance and Antiresonance in Electronic Transport Process Through a T-Shaped Quantum Waveguide

By means of the transfer matrix approach, the linear conductance spectrum for electronic transport through a T-shaped quantum waveguide is calculated. The resonant peaks and the antiresonant dips in the conductance spectrum are mainly focused. The previous prediction about their positions by other theoretical approaches is checked. In addition, a function of spin filtering is suggested based on the interplay of the resonance and antiresonance in this T-shaped quantum waveguide.     

Acoustic phonons transport in a quantum waveguide embedded double defects

By using scattering matrix method, we investigate the acoustic phonons transport in a quantum waveguide embedded double defects at low temperatures. When acoustic phonons propagate through the waveguide, the total transmission coefficient versus the reduced phonon frequency exhibits a series of resonant peaks and dips, and acoustic waves interfere with each other in the waveguide to form standing wave with particular wavelengths. In the waveguide with void defects, acoustic phonons whose frequencies approach zero can transport without scattering. The acoustic phonons propagating in the waveguide with clamped material defects, the phonons frequencies must be larger than a threshold frequency. It is also found that the thermal conductance versus temperature is qualitatively different for different types of defects. At low temperatures, when the double defects are void, the universal quantum thermal conductance and a thermal conductance plateau can be clearly observed. However, when the double defects consist of clamped material, the quantized thermal conductance disappears but a threshold temperature where mode 0 can be excited emerges. The results can provide some references in controlling thermal conductance artificially and the design of phonon devices.     

Acoustic phonons transport in a quantum waveguide embedded double defects

By using scattering matrix method, we investigate the acoustic phonons transport in a quantum waveguide embedded double defects at low temperatures. When acoustic phonons propagate through the waveguide, the total transmission coefficient versus the reduced phonon frequency exhibits a series of resonant peaks and dips, and acoustic waves interfere with each other in the waveguide to form standing wave with particular wavelengths. In the waveguide with void defects, acoustic phonons whose frequencies approach zero can transport without scattering. The acoustic phonons propagating in the waveguide with clamped material defects, the phonons frequencies must be larger than a threshold frequency. It is also found that the thermal conductance versus temperature is qualitatively different for different types of defects. At low temperatures, when the double defects are void, the universal quantum thermal conductance and a thermal conductance plateau can be clearly observed. However, when the double defects consist of clamped material, the quantized thermal conductance disappears but a threshold temperature where mode 0 can be excited emerges. The results can provide some references in controlling thermal conductance artificially and the design of phonon devices.     

Microwave-mediated heat transport in a quantum dot attached to leads

The thermoelectric effect in a quantum dot (QD) attached to two leads in the presence of microwave fields is studied by using the Keldysh nonequilibrium Green function technique. When the microwave is applied only on the QD and in the linear response regime, the main peaks in the thermoelectric figure of merit and the thermopower are found to decrease, with the emergence of a set of photon-induced peaks. Under this condition the microwave field cannot generate heat current or electrical bias voltage. Surprisingly, when the microwave field is applied only to one (bright) lead and not to the other (dark) lead or the QD, heat flows mostly from the dark to the bright lead, almost irrespective of the direction of the thermal gradient. We attribute this effect to microwave-induced opening of additional transport channels below the Fermi energy. The microwave field can change both the magnitude and the sign of the electrical bias voltage induced by the temperature gradient.     

Enhancement of the thermoelectric figure of merit in a quantum dot due to external ac field

We investigate the figure of merit of a quantum dot (QD) system irradiated with an external microwave filed by nonequilibrium Green?s function (NGF) technique. Results show that the frequency of microwave field influence the figure of merit ZT significantly. At low temperature, a sharp peak can be observed in the figure of merit ZT as the frequency of ac field increases. As the frequency varies, several zero points and resonant peaks emerge in the figure of merit ZT. By adjusting the frequency of the microwave field, we can obtain high ZT. The figure of merit ZT increases with the decreasing of linewidth function Γ. In addition, Wiedemann–Franz law does not hold, particularly in the low frequency region due to multi-photon emission and absorption. Some novel thermoelectric properties are also found in two-level QD system.