Design of Quantum Information Processing Devices Utilizing Electron Spins by Electric and Magnetic Fields

从应用于量子信息处理的观点出发，我们进行了各种基础研究，以控制半导体量子点中的电子自旋。1.我们提出了一个新的自旋注入的想法，使用一个小的收缩，量子点接触（QPC），制造在半导体上。既不需要磁场也不需要磁性材料。通过对存在自旋-轨道相互作用的QPC输运的数值研究，我们表明：（i）电导量子化被观察到，（ii）电流在横向上是自旋极化的，（iii）在InGaAs异质结构中可以实现超过50%的自旋极化. 2.电子自旋在硅中具有较长的相干时间，这是与化合物半导体相比用于量子信息处理的优势。我们数值研究了硅量子点中的电子态，考虑到电子-电子相互作用。我们已经证明，离散能级是度 ...更多信息 产生反射导带的多谷结构，结果，容易实现高自旋态。3.考虑到量子点中电子与核自旋的超精细相互作用，我们提出了电流驱动的核自旋纠缠机制。我们的机制是相关的泄漏电流在双量子点与泡利自旋封锁。伴随着自旋翻转的电流逐渐增加核自旋之间的量子相关性，这显著提高了电子的自旋翻转速率，从而提高了漏电流。4.研究了电子-声子相互作用对嵌入量子点的Aharonov-Bohm环非平衡输运的退相效应。用非平衡绿色函数成功地解释了在高偏压下Fano共振由非对称变为对称的实验结果。5.我们还通过铁磁金属制成的QPC进行了电导的数值研究，耦合量子点中量子门操作的数值模拟，单分子器件中外部电极对碳纳米管影响的研究等。

From a viewpoint of application to quantum information processing, we have performed various basic researches to control electron spins in semiconductor quantum dots. 1. We have proposed a new idea of spin injection using a small constriction, quantum point contact (QPC), fabricated on semiconductors. Neither magnetic fields nor magnetic materials are required. By numerical studies of the transport through a QPC in the presence of spin-orbit interaction, we have shown that (i) the conductance quantization is observed, (ii) the current is spin-polarized in the transverse direction, and (iii) spin polarization of more than 50% can be realized in InGaAs heterostructures. 2. Electron spins have a long coherent time in silicon, which is an advantage for quantum information processing compared with compound semiconductors. We have numerically studied electronic states in silicon quantum dots, taking into account electron-electron interaction. We have shown that discrete energy levels are deg … More enerate reflecting a multi-valley structure of conduction band and, as 'a result, high spin states are easily realized. 3. Considering the hyperfine interaction between electron and nuclear spins in quantum dots, we have proposed an entanglement mechanism of nuclear spins driven by the electric current. Our mechanism is relevant to a leakage current in double quantum dots with Pauli spin-blockade. The current accompanied by the spin flip gradually increases a quantum correlation among nuclear spins, which markedly enhances the spin-flip rate of electrons and hence the leakage current. 4. We have investigated the dephasing effect by electron-phonon interaction on nonequilibrium-transport in an Aharonov-Bohm ring with an embedded quantum dot. Using nonequilibrium Green function, we have successfully explained the experimental result that an asymmetric shape of Fano resonance is changed to a symmetric shape under high bias voltages. 5. We have also performed numerical study of electric conductance through a QPC made of ferromagnetic metals, numerical simulation of quantum gate operations in coupled quantum dots, study of the influence of external electrodes on carbon nanotubes in single molecule devices, etc. Less