Occurrence control of charged exciton for a single CdSe quantum dot at cryogenic temperatures on an optical nanofiber

We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The present photocharging method may open a new route to applying the CdSe quantum dots in quantum photonics, and the hybrid system of photocharged quantum-dot and optical nanofiber may readily be applicable to a fiber-in-line single-photon generator

Coherent interaction of orthogonal polarization modes in a photonic crystal nanofiber cavity

We show that coherent interaction between two sets of multiple resonances leads to exotic resonant effects, such as Fano-type resonances, optical analogue of electro-magnetically induced transparency, and avoided crossing between modes, under different coupling regimes. We experimentally demonstrate such resonant effects in a photonic crystal nanofiber cavity using two sets of cavity modes with orthogonal polarizations. The interaction between the modes arises due to intra-cavity polarization mixing. The observed line shapes are reproduced using a multiple-mode interaction model. Such spectral characteristics may further enhance the capabilities of the nanofiber cavity as a fiber-in-line platform for nanophotonics and quantum photonics applications

Nanofiber quantum photonics

Recent advances in the coherent control of single quanta of light, photons, is a topic of prime interest, and is discussed under the banner of quantum photonics. In the last decade, the subwavelength diameter waist of a tapered optical fiber, referred to as an optical nanofiber, has opened promising new avenues in the field of quantum optics, paving the way toward a versatile platform for quantum photonics applications. The key feature of the technique is that the optical field can be tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This feature has led to surprising possibilities to manipulate single atoms and fiber-guided photons, e.g. the efficient channeling of emission from single atoms and solid-state quantum emitters into the fiber-guided modes, high optical depth with a few atoms around the nanofiber, trapping atoms around a nanofiber, and atomic memories for fiber-guided photons. Furthermore, implementing a moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity quantum electrodynamics to be reached, and the long-range dipole–dipole interaction between quantum emitters mediated by the nanofiber offers a platform for quantum nonlinear optics with an ensemble of atoms. In addition, the presence of a longitudinal component of the guided field has led to unique capabilities for chiral light–matter interactions on nanofibers. In this article, we review the key developments of the nanofiber technology toward a vision for quantum photonics on an all-fiber interface

電気通信大学の21世紀COEプログラム「コヒーレント光科学の展開」

We describe the outline of the 21st Century COE Program at the University of Electro-Communications, "Innovation in Coherent Optical Science" which has been started in the fiscalyear of 2003

Silent elongation of polyrotaxane and its composites

Polyrotaxanes (PR) have attracted great interest due to their unique mechanical properties, exhibiting the pulley effect, via their slide-ring topological structure. Flexible and functional composite materials consisting of PR and inorganic particles, particularly those with plasma-surface modifications, have also shown higher toughness, even with large amounts of inorganic particles present. In this study, we verified the effect of neat PR and its composites with graphene nanoplates or carbon nanofibers by measuring acoustic emission (AE). Simultaneous AE and tensile measurements were tested several times for each sample, and AE signals during elongation were acquired. It revealed that the conventional fixed cross-linked elastomer materials showed AE signals in the entire tensile region, while the movable-cross-linked materials of PR showed almost no AE signal counts. This suggests that neat PR had almost no microscopic fracture before final breakage via the pulley effect. PR composites with plasma-surface-modified fillers showed a lower number of AE signals than that with unmodified fillers. This might be due to the surface modification of fillers, which improved filler dispersibility and/or prevented a large drop in the mobility of cross-linking points