| Budget Amount *help |
¥20,100,000 (Direct Cost: ¥20,100,000)
Fiscal Year 2005: ¥5,100,000 (Direct Cost: ¥5,100,000)
Fiscal Year 2004: ¥10,200,000 (Direct Cost: ¥10,200,000)
Fiscal Year 2003: ¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 2002: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
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
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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
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