By incorporating quantum coherence in the process, optical responses can be manipulated beyond the conventional limit. We demonstrated the basic principle using atomic hydrogen. In this project, we extend the physics of quantum coherence to condensed phases. Key issue of the project is to use solid hydrogen as the medium. Solid hydrogen is a molecular crystal making up of H2-molecules and is known as a quantum crystal.

Photographs (right) exhibit emission patterns observed for stimulated Raman scattering in solid hydrogen. Blue ring is a conventional phase-matched anti-Stokes component. Other than the blue ring, much stronger blue spot is observed. This blue spot does not satisfy the conventional phasematching, and it is a clear manifestation of the quantum coherence effect. Furthermore, using well-controlled quantum coherence in solid hydrogen, we can slow down the pulse speed of light to c/30,000 and can efficiently generate parametric sidebands even for incoherent fluorescence light.

We are exploring taper-fiber technology to apply for quantum optics. The point is to prepare a very thin part with a subwavelength diameter along the fiber. Left figure illustrates a schematic diagram. The very thin part is embedded in an optical medium. Light propagating in the fiber interacts with the medium through evanescent field in the very thin region. We can manipulate quantum coherence of the medium through the evanescent field and can control the quantum optical behaviors of the propagating light.