Overview of Quantum Optics and Optical Materials Research

Takaaki Mukai
Physical Science Laboratory

    In the fields of quantum optics and optical materials we pursue our studies for the development of core-technologies that will innovate optical communications and optical signal processing as well as for the scientific progress of the field. Optical State Control Research Group, Ultrafast Optical Physics Research Group and Optical Device Physics Research Group are engaged in the subjects listed below.

Quantum State Control Research Group
(1)Quantum communication and information processing (proposal and verification of a new quantum cryptography, studies on quantum protocols, quantum entanglement, and quantum computing).
(2)Atom optics (experimental and theoretical studies on Bose-Einstein condensation of alkali atoms, and control of new quantum states by laser lights).

Ultrafast Optical Physics Research Group
(1)High-irradiance soft X-ray generation from femtosecond laser-produced plasma and its application to materials science (demonstration of high-irradiance soft X-ray pulse generation and table-top soft X-ray laser, clarification of soft X-ray generation mechanism, and demonstration of time-resolved soft X-ray spectroscopy).
(2)Ultrafast laser pulse induced terahertz radiation and its application

Optical Device Physics Research Group
(1)Coherent control of excitonic and spin states in quantum dots (optical Rabi oscillations in a zero-dimentional exciton, experimental study of excitonic properties of quantum dots, spin-polarized electron transport in quantum wires).
(2)Optical properties in nitride-semiconductors and their device applications (optical properties of nitride quantum wells, including excitonic and piezo-electric effects, and nitride photo-conductive detector).
(3)Nano-scale fabrication process for photonic crystal materials (dry etching process for damage-free surfaces of GaAs and GaN, and design and fabrication of photonic crystal structures).

    Major results obtained this fiscal year 2000 are reported in the following pages. We investigated strong gain saturation behavior in fiber optical parametric amplification and demonstrated its application to noise suppression and optical limiter operations. Parametric process in optical fiber is promising for the generation of quantum entangled photon twins for quantum communications.
    Nanostructure-array targets were employed to create larger-volume plasm with high-local-density, compared with those from flat target, in X-ray generation from femtosecond-laser-produced plasma, resulting in large soft x-ray conversion efficiency as well as suppression of broadening of generated x-ray pulse duration.
    We demonstrated long-lived exciton coherence more than 40 ps in a single isolated InGaAs quantum dot. Favored by this long-lived coherence, we clearly observed exciton Rabi oscillation, i.e., coherent population flopping induced by the strong coupling light resonant to excitonic discrete level. This promises the coherent control of the quantum states in semiconductor quantum dots applicable to quantum computation.

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