04 (2012 Selected)：

Development of element technologies and elucidation of physics toward realization of silicon quantum bits

Study of quantum computation using electron spins in quantum dots has been led by GaAs quantum dot (QD) systems so far. However, it needs to be expanded to silicon-based QD systems in the future when a problem of decoherence by nuclear spins and the compatibility to the current technologies of electronics are taken into account. In order to advance more rapidly this research, it is essential to successfully apply the technologies and the physical knowledge which have been obtained in GaAs QD systems, to silicon QD systems. In this study, we design and fabricate silicon QD devices in a few-electron regime and characterize the transport properties. In addition, we aim spin manipulation and readout by high-frequency voltage operation on the basis of experiences in GaAs QDs.

In this study, we focus on the physical comparison between silicon QDs and GaAs QDs. More concretely, we study decoherence factors specific to the silicon QDs and modulation range of tunnel coupling and exchange coupling. From the magnetic field dependence of the single QDs, we clarify the electronic states specific to silicon. In addition, we observe spin blockade phenomena by controlling the tunnel coupling in double QDs. We study how the magnetic field dependence of the leakage current in the spin blockade region differs from that in GaAs QDs, and then discuss the effect of valley degeneracy on spin decoherence in silicon QDs. As element technologies, we develop the technology to fabricate silicon QDs, where the single electron state can be controlled with high precision, high stability, and low noise. We also develop technologies for high frequency operation and readout of the individual electron spin states.

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