Novel nonclassical light, indistinguishable single photons and entangled photons are generated on demand with a single quantum dot microvacity device   and successfully applied to quantum key distribution systems  and fundamental test of quantum mechanics. The system replacing a quantum dot with an ensemble of impurities is expected to realize efficient quantum memory and quantum repeater systems. Optical pumping and optical detection of nuclear spins in solids are studied toward realization of a large-scale solid state NMR quantum computer.  Preliminary results are encouraging in terms of high nuclear polarization and long decoherence time.
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