Nano- and atom-photonics: Beyond the fundamental limit of light

元一 大津, Motoichi Ohtsu

Masud Mansuripur

The fundamental processes of absorption, stimulated and spontaneous emission, and elastic as well as inelastic scattering involving light and atoms, molecules, and nano-particles have been studied for decades using both classical and quantum theories. While providing an overview of the subject, this paper presents a streamlined approach to studying atom-photon interactions in the context of modern quantum optics in the hope of providing guidance for applications in the general area of molecular and nano-photonic machines.

Su‐Peng Yu

Development of technology can allow access to new regimes in science and creation of new fields of research. The development of ultra-high finesse mirror technology enabled the development of the field of cavity quantum electrodynamics, and an abundance of wonderful physics experiments soon followed. The sophistication of the field of nano-fabrication and nano-photonics would allow unprecedented capability to mold the shape and flow of light, and provide a novel platform for efficient and hopefully integrable quantum systems. In this project, we hope to interface cold atoms, perhaps the most quintessential of quantum systems, to the engineering power of nano-photonics. We believe this field of study will not only lead to the demonstration of new physics in the quantum regime, but work toward building a network with quantum capabilities mediated by optical channels. In this project, we develop a nano-fabricated platform capable of interfacing nano-photonic devices with cold Cesium atoms in free-space. Nano-photonic waveguide devices are fabricated in a Silicon Nitride device layer on Silicon substrate. The fabrication is compatible with conventional semiconductor fabrication processes, and the chip design has been adapted to allow incorporation with free-space optics to support cold Cesium atom cloud around the waveguides. An ultra-high vacuum system that is compatible to the chip and its supporting structures was constructed to perform experiments. With our system, we were able to fabricate and characterize nano-photonic structures, including 1D photonic crystal waveguides, cavities, and 2D photonic crystal slabs. For the 1D photonic crystal waveguide devices, enhanced atom-light coupling between localized Cesium atoms in the vicinity of the devices, and also atom-atom interaction between Cesium atoms mediated by the guided mode of the photonic crystal waveguide, has been observed. The 2D photonic devices allow us many capabilities beyond that of the 1D waveguide. Demonstration of exotic optical properties including natural decay rate suppression and circular polarization engineering, should be within reach in the near future.

Manukumara Manjappa, C. M. Chandrashekar, Ambarish Ghosh +1 more

Motoichi Ohtsu, Kiyoshi Kobayashi

Motoichi Ohtsu

Optical disk memory, optical fiber communication systems, and photolithography are examples of success in photonics. In the case of optical disk memory, storage and readout of the pit size smaller than λ/NA are not possible, where λ and NA are the wavelength of the incident light and a numerical aperture of the focusing lens, respectively. Shorter-wavelength lasers have been intensively developed in order to decrease the diffraction-limited pit size, i.e., the major efforts of increasing storage density have been how to use the shorter-wavelength light for storage and readout. However, the upper limit of the storage density to be realized by using visible light is several 10 Gb/in.2, while the value to be required in the year 2010 is 1 Tb/in.2. Semiconductor lasers, optical waveguides, and optical switching devices have to confine the light in their bodies for effective operations. In the case of a semiconductor laser, its active layer has to be larger than the diffraction-limited volumes, i.e., λ3, for this confinement. In the case of an optical fiber, its core diameter has to be larger than λ. These examples mean that the sizes of photonic devices cannot be smaller than the wavelength of light, which is the diffraction-limited size of the photonic device. However, sizes of photonic switching devices for the optical fiber communication system in the year 2015 must become smaller than the diffraction-limited ones. The most narrow linewidth of the pattern fabricated by photolithography is also limited by diffraction. Progress in decreasing the patterned size has been the result of the effort of using shorter-wavelength light for decreasing the diffraction-limited value. However, further shortening of the wavelength requires gigantic and expensive light sources, which can prohibit developing practical microfabrication systems. For the visible light sources, the 30–70-nm linewidth for 64–256 GbDRAMs is far beyond the diffraction limit. To summarize, the society of the twenty-first century requires a novel optical technology in order to realize measurement, fabrication, control, and function with the size of several tens of nanometers. However, such miniaturization of optical technology is not possible as long as the conventional propagating light is used. This is the bottleneck imposed by light diffraction. One must go beyond the diffraction limit in order to open a new field of optical technology; this field is called as “nanophotonics.”