一维量子点阵列的自旋链上信息传输

基于紧束缚模型的实空间格点组成的一维线性均匀有序的量子点阵列为研究对象,然后利用演化算符的作用使其在量子点阵列的自旋链上进行单量子比特的信息传输。即使用演化算符 使单比特量子态从量子点阵列起始端为多粒子态 传输到末端态为 ,最后在此基础上计算概率来讨论了单量子比特能从起始端的多粒子态 的第一个量子比特完全传输到态 的末端第N个量子比特是可能的。     

任意态量子信息在自旋链上的传输

量子信息传输是量子信息的一个重要分支。以自旋链上单态量子信息的传输为基础,详细讨论了两态和三态信息在自旋链上的传输,并进一步推广至任意态的情形。最终得出在自旋链上两态、三态乃至任意多态的量子信息传输的概率公式,以及自旋链完备传输任意态信息的条件。从而为任意多态量子信息的完备传输提供了一套切实可行的理论方案。     

基于非调制自旋链的量子通信

研究在热平衡状态下,外加均匀静态磁场度和自旋粒子间的耦合度对系统的保真度和纠缠度的影响,提出如何利用它们之间的关系来提高自旋系统中量子态的传输质量。研究结果表明采用非调制自旋链作为长程相互作用自旋系统中量子态的传输信道,量子态的保真度随着自旋粒子间耦合系数的增加而增加,外加静态磁场强度在0~1的范围内时,量子态传输的失真较小。因此在热平衡状态下,选取适当的耦合度和外加均匀磁场强度,无需对自旋系统进行任何操作即可实现量子态的高质量传输。     

非马尔科夫环境中海森堡自旋链的纠缠动力学

利用Diosi、Gisin提出的非马尔科夫量子态扩散方法,精确地模拟了在余弦磁场与Dzyaloshinskii-Moriya(DM)相互作用时,处于非马尔科夫环境中的两比特各向异性海森堡XYZ模型纠缠动力学的演化过程.采用最大纠缠态|Ψ﹥=12(|00﹥+|11﹥)作为系统所处的初始态,详细地讨论了不同的环境关联系数γ...     

直线法分析一维非均匀矩形波导的传输特性

用直线法对一维非均匀矩形波导进行了分析,由传递矩阵获得了该波导不同模式的特征方程.以部分非均匀介质填充的矩形波导为例,对其色散特性和截止特性进行了数值计算和分析,验证了该方法的正确性.对研究非均匀波导问题有参考价值.     

具有Stubs结构量子波导中电子的自旋传输特性

利用递归格林函数法研究了含Rashba自旋轨道耦合效应的具有Stubs结构的量子波导中电子的自旋极化传输特性.结果表明在含一个stub的量子波导系统中, 由于stub和Rashba自旋轨道耦合引起的势阱导致系统电导出现Fano共振形式的“山谷”和“针尖”结构, 通过改变自旋轨道耦合的强度可以调节它们的大小. 同时,在同样的位置自旋极化率也出现Fano共振或反共振结构. 当系统中出现多个周期性的stubs时, 在Fano共振点附近电导中出现一些小的带隙结构.但是,当系统加上磁场后, stubs和自旋轨道耦合带来的效应都被抑制, 系统的电导重新出现量子化台阶结构. 同时由于子带间干涉效应变小, 自旋电导也出现台阶结构.     

非均匀磁场下不同自旋轨道耦合相互作用对高自旋系统热纠缠的影响

采用纠缠的度量方法negativity研究了非均匀磁场条件下不同方向自旋轨道耦合相互作用对自旋为1的Heisenberg XX系统热纠缠的影响。研究发现高温时纠缠会随着Dzialoshinskii-Moriya(DM)相互作用的增加而增大,但是低温时,纠缠随DM相互作用的增加会出现起伏变化。x方向DM相互作用的纠缠一般较z方向DM相互作用的纠缠强,但是在一定条件下,z方向的纠缠也会高于x方向的纠缠,从而可以通过调节DM相互作用的方向等控制和生成纠缠、研究还发现可以利用纠缠关于磁场的对称性质以及纠缠的突变性来实现量子逻辑门、     

非均匀磁场下不同自旋轨道耦合相互作用对高自旋系统热纠缠的影响

采用纠缠的度量方法Negativity研究了非均匀磁场条件下不同方向自旋轨道耦合相互作用对自旋为1的Heisenberg XX 系统热纠缠的影响。研究发现高温时纠缠会随着Dzialoshinskii–Moriya（DM）相互作用的增加而增大,但是低温时,纠缠随DM相互作用的增加会出现起伏变化。x方向DM相互作用的纠缠一般较z方向DM相互作用的纠缠强,但是在一定条件下,z方向的纠缠也会高于x方向的纠缠,从而可以通过调节DM相互作用的方向等控制和生成纠缠。研究还发现可以利用纠缠关于磁场的对称性质以及纠缠的突变性来实现量子逻辑门。     

（英）嵌有两个量子点的三终端量子环中的横向自旋流

从理论上研究了一个上臂与下臂各嵌有一个量子点的三终端三臂量子环中的自旋极化的电子输运性质.考虑了两个量子点中的库仑互作用并假设在某一个环臂中存在Rashba自旋轨道耦合作用.利用非平衡态格林函数方法,发现不需要借助任何磁场与磁性物质Rashba自旋轨道耦合作用导致的量子干涉效应就可以从器件中驱动出一个自旋流.适当调节外加偏压、Rashba自旋轨道耦合作用强度以及量子点能级等系统参数时器件中甚至还可以产生完全自旋极化电流或纯自旋流.另外,还讨论了系统参数对自旋流大小、符号、自旋极化度以及峰值的影响.     

基于单边选择链和样本分布密度融合机制的非平衡数据挖掘方法

非平衡数据集分类问题是机器学习领域的重大挑战性难题.针对该难题,传统的少数类样本合成技术（Synthetic Minority Over-Sampling Technique,SMOTE）已成为一种有力手段并得到广泛采用.但在新样本生成过程中,SMOTE利用所有少数类样本合成新样本,由此产生过拟合瓶颈.为更好地解决该问题,提出了一种基于单边选择链和样本分布密度的非平衡数据挖掘新方法（One-Sided Link & Distribution Density-SMOTE,OSLDD-SMOTE）.OSLDD-SMOTE通过单边选择链遴选出处于分类边界的少数类样本,根据这些样本的动态分布密度生成新样本.进而分析了样本合成度对节点数目和对少数类精度的影响;基于G-mean、F-measure和AUC三个指标综合比较了OSLDD-SMOTE与其他同类方法的分类性能.实验结果表明,OSLDD-SMOTE有效提高了少数类样本的分类准确率.     

Light-driven molecular motion modifying the electronic structure and spin properties of solid organic superstructure

The polarized light acted as one of the non-contacted media could effectively tune the crystal structure to improve the physical properties. In this work, under polarized laser excitation, the molecular motion is driven inside the crystals, where the electronic structure of the crystal is affected to further change the spin and optical properties. However, decreasing the temperature to 77 K, the external polarized laser cannot produce direct molecular motion. Moreover, switching the incident laser from the linearly to circularly polarized state, the dependence of the molecular motion on the spin and optical properties show pronounced difference.     

The length and hydrogenation effects on electronic transport properties of carbon-based molecular wires

It is known that the conductance of a wire decreases linearly with the increase of its length in the macro circuit. But things are different in mesoscopic field, especially in molecular dimensional circuits due to the quantum interferences in molecular size. In this work, first principles is used to investigate how wire length and hydrogenation degree influence the conductance of molecular wires. For comparison, two types of carbon-based molecular wires, single carbon atomic wire and phenyl ring wire with single hydrogenation or dihydrogenation, are chosen and coupled to two zigzag graphene nanoribbon electrodes, respectively. We show that the conductance of zigzag carbon atomic wire with single hydrogenation exhibits an evident even-odd oscillatory behavior with the increase of wire length, while that of phenyl ring wire starts to increase before decreasing. However, when the above types of wires are edged with dihydrogenation, their conductance decreases exponentially with the increasing wire length. In addition, fine current rectification is found in asymmetric phenyl wires induced by hydrogenation degree, which can be used as diode in future molecular devices. Analyses via orbital hybridization, transmission path, HOMO-LUMO position and so on reveal the microscopic mechanism of the above interesting results.     

Modulation of the spin transport properties of the iron-phthalocyanine molecular junction by carbon chains with different connection sites

Based on the non-equilibrium Green's function method combined with the density functional theory, the spin transport properties of an iron-phthalocyanine (FePc) molecule connected to two Au electrodes by carbon chains are investigated, and three kinds of connecting position between FePc molecule and carbon chains are considered. It is found that the spin filtering effect and the negative differential resistance (NDR) behavior in these systems can be achieved in the calculated bias region. However, the efficiency and the bias region of spin filtering are affected significantly by the connecting positions. The above results are explained by the spin-resolved transmission spectrum, electron transmitting path, molecular projected self consistent Hamiltonian state, and the local density of states (LDOS) analyses. Our calculations demonstrate a promising modification for developing molecule spintronic devices.     

Phase characterization and dielectric properties of a copper-cordierite electronic packaging system

Dielectric properties, microstructure and the nature of crystallized phases were investigated in Cu or Cu₂O-cordierite (MgO-Al₂O₃-SiO₂) glass ceramic materials of interest in microelectronic packaging. Cu and Cu₂O powders were dispersed (0 to ∼3 wt.%) in a frit of cordierite based glass and processed to form the ceramic with small amounts of Cu or Cu₂O inclusions. Samples were fired at 1000° in air (group 1), reducing atmospheres of Po₂ ≃10^-11 atm (group 2) and P_{O 2}< 10^-15 atm (group 3). X-ray diffraction, STEM and EDS analyses of the fired ceramics showed the presence of α-cordierite (major phase), minor amounts of enstatite, forsterite, α-alumina and phase separated areas. Dielectric constants of all samples in group 1 and 3 were measured to be ∼5.9 at 25° in the frequency range 1 kHz to 3.5 MHz. Cu or Cu₂O additions did not significantly affect the dielectric constant but the presence of some porosity decreased the dielectric constant to 4.7 to 5.2.     

Galvanomagnetic and thermoelectric properties of BiTeBr and BiTeI single crystals and their electronic structure

BiTeI and BiTeBr single crystals are synthesized by the Bridgman method, and their galvanomagnetic and thermoelectrical properties are investigated. Both semiconductors have n-type conductivity. The thermoelectric efficiency of BiTeBr is much higher than that of BiTeI, which is related mainly to a larger See-beck coefficient for the former compound. For both crystals, the band structure is calculated from the density-functional theory. It is shown that both compounds are semiconductors with an indirect energy band gap.     

The relationship between intermolecular interactions and charge transport properties of trifluoromethylated polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) with the electron-withdrawing groups such as halogen atom, cyanide, perfluoroalkyl (PFA), or perfluoroary, etc. exhibit good air stability and better solid-state charge carrier mobility. To obtain a better understanding of structure property relationships of this kind of compounds, a series PAH(CF₃)_n derivatives a1, a2, b1, b2, c1, and c2, which contain different numbers of trifluoromethyls and benzene rings, were chosen and studied by both band-like model and hopping model. Their crystals contain different intermolecular interactions. It turns out that intermolecular hydrogen bonding interactions are mainly responsible for electron transport, while π-stacking interactions dominate hole transport. When the π-stacking and intermolecular hydrogen bonding interactions coexist in the same direction, a competitive relationship occurs between hole and electron transport, which tend to cause enhancement of electron transport, and restrain hole transport.     

Tuning of the electronic and transport properties of phosphorene nanoribbons by edge types and edge defects

By performing first-principle quantum transport calculations, we investigated the effects of the edge types and edge defects on the electronic and transport properties of phosphorene nanoribbons (PNRs). The calculated band structures show the PNRs with the zigzag and cliff edges are all metallic. The conductance of the cliff phosphorene nanoribbon (CPNR) is higher than that of the zigzag phosphorene nanoribbon (ZPNR). The low bias negative differential resistance behavior is only found in the ZPNR and the peak-to-valley current ratio is up to 10². More over, we found the carrier transport channels under low bias of ZPNR and CPNR mainly locate on the edges. The current-voltage characteristics show the defects induced by removing the phosphorus atoms from the edge can decrease the conductance of the ZPNR and CPNR obviously. The low bias negative differential resistance behavior of the ZPNR also can be weakened or removed by the edge defects.     

First-principles study on the electronic, elastic and thermodynamic properties of three novel germanium nitrides

The ultrasoft pseudo-potential plane wave method combined with the quasi-harmonic approach have been used to study the electronic, elastic and thermodynamic properties of the tetragonal, monoclinic and orthorhombic Ge₃N₄. The negative formation enthalpies, the satisfactory of Born''s criteria and the linear variations of elastic constants with pressure indicate that the three polymorphs can retain their stabilities in the pressure range of 0-25 GPa. The three Ge₃N₄ are brittle solids at 0 GPa, while they behave in ductile manners in the pressure range of 5-25 GPa. t- and o-Ge₃N₄ are hard materials but anisotropic. m-Ge₃N₄ has the largest ductility among the three phases. The results reveal that m-Ge₃N₄ belongs to an indirect band gap semiconductor, while t- and o-Ge₃N₄ have direct band gaps. For the thermal properties, several interesting features can be observed above 300 K. o-Ge₃N₄ exhibits the largest heat capacity, while m-Ge₃N₄ shows the highest Debye temperature. The results predicted in this work can provide reference data for future experiments.     

Influence of polar molecular chain orientation on optical and carrier transport properties of polymer blends

We report investigation of optical and electrical properties of poly(9-vinylcarbazole) (PVK) doped with 30 wt% 4-dibutylamino-4′-nitrostilbene (DBANS), depending on the molecular chain orientation of polar DBANS molecules. Orientation of dopant diode-like DBANS dye molecules was achieved by application of a static electric field through the polymer film, while heating the material near its glass transition temperature (T_g). Modification of optical properties due to the orientation was evidenced by the spectral dependencies of absorption coefficient. Appearance of the orientation-induced built-in electrical field was proven optically by the solid electric field induced second harmonic generation (SEFISHG) and electrically by current–voltage (IV) characterization. Measurement of the thermally stimulated currents (TSC) spectra demonstrated that carrier transport and trapping are affected, too. Changes of the TSCs induced by orientation were expressed best in the temperature range of 280–290 K. They could be attributed to the thermally activated process with activation energy of about 0.38 eV.     

Control of growth and charge transport properties of quaterthiophene thin films via hexyl chain substitutions

Growth mechanism of quaterthiophene based organic thin films deposited by high vacuum deposition on Si:H(1 0 0) and SiO₂ substrates have been investigated. Especially the influence of hexyl chain end-substitutions on the growth process and the electronic transport properties of organic thin films were studied in details. Highly crystalline films were obtained for both quaterthiophene (4T) and α,ω-hexyl-quaterthiophene (DH4T) based thin films. While unsubstituted 4T shows a typical island growth, an almost perfect layer-to-layer growth was found in the case of DH4T based films. It could be demonstrated that the change in the growth mode is directly related to the molecule structure, i.e. to the presence of hexyl chain substitutions on the 4T core, and leads to an increase of the grain size of one order of magnitude under the same evaporation conditions in the case of DH4T films. The characterization of the charge transport properties of thin films based on both molecules reveals one order of magnitude higher mobilities for the DH4T molecules. By using a simple model for charge transport in polycrystalline materials a linear dependence of the mobility on the grain size, independently from the molecule substitution, could be demonstrated. The results underline the importance of the control of the film morphology and give an impressive example of such a control in the case of hexyl end-substitutions of quaterthiophene.