Overview of Quantum Optics and Optical Materials Research

Yoshiro Hirayama
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, Optical Device Physics Research Group and Photonic Nanostructure Research Group are engaged in the subjects listed below.

Quantum State Control Research Group
(1) Experimental and theoretical studies for quantum cryptography/computing/protocols.
(2) Quantum transport theory and electron/spin entanglement.

Ultrafast Optical Physics Research Group
(1) High-irradiance, short-pulse soft X-ray generation from femtosecond laser-produced plasma and its application to materials science.
(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 & wires.
(2) Optical properties in nitride-semiconductors and their device applications.
(3) Single/entangled photon emitters and detectors.

Photonic Nanostructure Research Group
(1) Two-dimensional photonic crystal optical circuits (ultra-low loss waveguide, resonator, filter)
(2) Interaction between photonic nanostructures and materials (negative refraction, extremely-large group velocity dispersion, photonic quasicrystal laser).
(3) Nanoprint lithography

 Major results obtained this fiscal year 2003 are reported in the following pages.
 We have demonstrated a long-distance quantum key distribution by using a single photon emitter based on quantum dots. We have also proposed and demonstrated a novel quantum cryptography scheme called differential-phase-shift quantum key distribution. This scheme will provide stable and high-speed quantum cryptography.
 Efficiency of water-widow x-ray pulse conversion from femtosecond laser plasma was successfully improved by using a carbon nanotube target. The result indicates that carbon nanotubes are attractive as fs-laser plasma target for realizing single-shot x-ray microscopy. Sampling measurement of femtosecond soft x-ray pulse, which is based on optical-field induced ionization dynamics, has been demonstrated.
 We combined GaN quantum wells with oxide-based distributed Bragg reflectors by using a wafer bonding technique. The VCSEL (vertical cavity surface emitting laser) operation was successfully demonstrated for the fabricated structures. We also started a new project for single and entangled photon emitters and detectors in collaboration with TAO (Telecommunications Advanced Organization of Japan).
 We have demonstrated ultra-low-loss photonic bandgap waveguide and developed ultra-small and high-Q filter based on SOI (silicon on insulator) photonic crystal systems. We have also fabricated photonic quasicrysytal lasers with organic dye and confirmed clear lasing action for the first time. Our experimental results indicate that lasing occurs by delocalized coherent modes inside the quasicrystal.

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