Fabrication and control of nuclear-and electron spin quantum bits

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We have performed fundamental research on quantum manipulation of 29Si nuclear spins that are artificially placed in a well-defined manner in isotopically controlled silicon single crystals. Here spin manipulation refers to as initialization (polarization enhancement) and extension of phase coherence time by appropriate irradiation of pulsed radio frequency sequences.As a first step, we have successfully understood physics of silicon surfaces for appropriate placing of specific silicon isotopes in a very well-defined manner and succeeded in realization of atomic arrays that were suitable for silicon nuclear spin quantum computation. We have also proposed new methods to initialize 29Si nuclear spins using either light or electron spin resonance, and confirmed their effectiveness experimentally by increasing the nuclear spin polarization by the three orders of magnitude. In parallel, we have succeeded in extension of the phase coherence time up to 25 seconds at room temperature. For the readout, we have proposed new methods based on light or electron spin resonance and experimentally demonstrated successful readout of the nuclear spin states in silicon.