Final-state read-out of exciton qubits by observing resonantly excited photoluminescence in quantum dots

We report on a new approach to detect excitonic qubits in semiconductor quantum dots by observing spontaneous emissions from the relevant qubit level. The ground state of excitons is resonantly excited by picosecond optical pulses. Emissions from the same state are temporally resolved with picosecond time resolution. To capture weak emissions, we greatly suppress the elastic scattering of excitation beams, by applying obliquely incident geometry to the micro photoluminescence set-up. Rabi oscillations of the ground-state excitons appear to be involved in the dependence of emission intensity on excitation amplitude.Comment: 4 pages, 4 figures, to appear in Appl. Phys. Let

Erratum to: Concentric Multiple Rings by Droplet Epitaxy: Fabrication and Study of the Morphological Anisotropy

We present the Molecular Beam Epitaxy fabrication of complex GaAs/AlGaAs nanostructures by Droplet Epitaxy, characterized by the presence of concentric multiple rings. We propose an innovative experimental procedure that allows the fabrication of individual portions of the structure, controlling their diameter by only changing the substrate temperature. The obtained nanocrystals show a significant anisotropy between [110] and [1–10] crystallographic directions, which can be ascribed to different activation energies for the Ga atoms migration processes

Self-Assembled Local Artificial Substrates of GaAs on Si Substrate

We propose a self-assembling procedure for the fabrication of GaAs islands by Droplet Epitaxy on silicon substrate. Controlling substrate temperature and amount of supplied gallium is possible to tune the base size of the islands from 70 up to 250 nm and the density from 107 to 109 cm−2. The islands show a standard deviation of base size distribution below 10% and their shape evolves changing the aspect ratio from 0.3 to 0.5 as size increases. Due to their characteristics, these islands are suitable to be used as local artificial substrates for the integration of III–V quantum nanostructures directly on silicon substrate

Production and antioxidative activity of alcoholic beverages made from Thai ou yeast and black rice (Oryza sativa var. Indica cv. Shiun)

Fermentation yeast was isolated from a Thai traditional alcoholic beverage called Thai ou, which is drunk through bamboo tubes. The isolated yeast was identified as a strain of the genus Saccharomyces cerevisiae. The alcoholic beverage made with the isolated yeast designated as S. cerevisiae NP01 from black rice grains had an ethanol concentration of 12.4 to 13.1% (v/v) and a large amount of phenolic compounds. The resulting alcoholic beverages made from black rice grains were red in color, especially those made from uncooked black rice, which had a brilliant red hue similar to that of red or rosé wine. The amount of anthocyanin in the beverages made from uncooked black rice with NP01 and industrial wine yeast W-4 was 118 and 131 μg/ml, respectively. The anthocyanin content of beverages made from uncooked black rice was higher than that of the beverages made from the cooked black rice. The antioxidative activity of alcoholic beverages made from uncooked black rice was also higher than that of beverages made from cooked black rice. In the course of this study, the use of NP01 yeast produced black rice wine that was red in color and exhibited antioxidative activity.Key words: Antioxidative activity, ou, black rice, anthocyanin, alcoholic beverage

GaAs Sub-Micron and Nano Islands by Droplet Epitaxy on Si

Merging the high effi?ciency light emitting III-V semiconductors with the state-of-the-art Silicon based electronics is of great interest for the realization of new optoelectronic devices. Unfortunately the heteroepitaxial growth of GaAs thin ?films on Si is a diffi?cult task because of the di?fference in the lattice constant, the polar/non-polar surface interaction and the di?fference in the thermal expansion coeffi?cients. We present for the ?first time the MBE growth of GaAs nanostructures on Si substrates by Droplet Epitaxy (DE) [1,2]. We believe this growth method to be promising for the growth of high quality GaAs nanoislands directly on Silicon. In the DE, the substrate is irradiated by a Ga molecular beam fl?ux ?first, leading to the formation of numerous fi?ne Ga droplets with uniform size, which are subsequently crystallized into GaAs nanostructures by an As molecular beam supply. By changing the Ga droplets deposition temperature is possible to change independently the size and the density of the droplets, while by varying the As ?flux for the crystallization we can change the fi?nal shape of the GaAs nanocrystals. We present the results for the growth of GaAs on Si by DE where the density of the GaAs nanoislands was changed by two orders of magnitude, while the size is varied from around 200 nm to around 20 nm. Measurements by X-ray microanalysis in the TEM con- fi?rmed the reaction between Ga and As with formation of GaAs. This has also seen by the presence of Moir? fringes in the TEM images taken in the two beam di?raction mode. The discontinuities of some Moir? fringes would suggest the presence of dislocations

Picosecond Nonlinear Relaxation of Photoinjected Carriers in a Single GaAs/AlGaAs Quantum Dot

Photoemission from a single self-organized GaAs/AlGaAs quantum dot (QD) is temporally resolved with picosecond time resolution. The emission spectra consisting of the multiexciton structures are observed to depend on the delay time and the excitation intensity. Quantitative agreement is found between the experimental data and the calculation based on a model which characterizes the successive relaxation of multiexcitons. Through the analysis we can determine the carrier relaxation time as a function of population of photoinjected carriers. Enhancement of the intra-dot carrier relaxation is demonstrated to be due to the carrier-carrier scattering inside a single QD.Comment: 4 pages, 4 figures, to be published in Phys. Rev. B, Rapid

Bunching visibility for correlated photons from single GaAs quantum dots

We study photon bunching phenomena associated with biexciton-exciton cascade in single GaAs self-assembled quantum dots. Experiments carried out with a pulsed excitation source show that significant bunching is only detectable at very low excitation, where the typical intensity of photon streams is less than the half of their saturation value. Our findings are qualitatively understood with a model which accounts for Poissonian statistics in the number of excitons, predicting the height of a bunching peak being determined by the inverse of probability of finding more than one exciton.Comment: 6 pages, 6 figs to appear in Phys. Rev.

Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background

Photoluminescence Study of Low Thermal Budget III–V Nanostructures on Silicon by Droplet Epitaxy

We present of a detailed photoluminescence characterization of high efficiency GaAs/AlGaAs quantum nanostructures grown on silicon substrates. The whole process of formation of the GaAs/AlGaAs active layer was realized via droplet epitaxy and migration enhanced epitaxy maintaining the growth temperature ≤350°C, thus resulting in a low thermal budget procedure compatible with back-end integration of the fabricated materials on integrated circuits