Two-photon- photoluminescence excitation spectroscopy of single quantum-dots

We present experimental and theoretical study of single semiconductor quantum dots excited by two non-degenerate, resonantly tuned variably polarized lasers. The first laser is tuned to excitonic resonances. Depending on its polarization it photogenerates a coherent single exciton state. The second laser is tuned to biexciton resonances. By scanning the energy of the second laser for various polarizations of the two lasers, while monitoring the emission from the biexciton and exciton spectral lines, we map the biexciton photoluminescence excitation spectra. The resonances rich spectra of the second photon absorption are analyzed and fully understood in terms of a many carrier theoretical model which takes into account the direct and exchange Coulomb interactions between the quantum confined carriers.Comment: Accepted for publication in PR

Complete control of a matter qubit using a single picosecond laser pulse

We demonstrate for the first time that a matter physical two level system, a qubit, can be fully controlled using one ultrafast step. We show that the spin state of an optically excited electron, an exciton, confined in a quantum dot, can be rotated by any desired angle, about any desired axis, during such a step. For this we use a single, resonantly tuned, picosecond long, polarized optical pulse. The polarization of the pulse defines the rotation axis, while the pulse detuning from a non-degenerate absorption resonance, defines the magnitude of the rotation angle. We thereby achieve a high fidelity, universal gate operation, applicable to other spin systems, using only one short optical pulse. The operation duration equals the pulse temporal width, orders of magnitude shorter than the qubit evolution life and coherence times.Comment: main text: 4 pages, 3 figures Supplemental material: 3 pages, 1 figur

Fouling mechanisms in constant flux crossflow ultrafiltration

Four fouling models due to Hermia (complete pore blocking, intermediate pore blocking, cake filtration and standard pore blocking), have long been used to describe membrane filtration and fouling in constant transmembrane pressure (ΔP) operation of membranes. A few studies apply these models to constant flux dead-end filtration systems. However, these models have not been reported for constant flux crossflow filtration, despite the frequent use of this mode of membrane operation in practical applications. We report derivation of these models for constant flux crossflow filtration. Of the four models, complete pore blocking and standard pore blocking were deemed inapplicable due to contradicting assumptions and relevance, respectively. Constant flux crossflow fouling experiments of dilute latex bead suspensions and soybean oil emulsions were conducted on commercial poly (ether sulfone) flat sheet ultrafiltration membranes to explore the models’ abilities to describe such data. A model combining intermediate pore blocking and cake filtration appeared to give the best agreement with the experimental data. Below the threshold flux, both the intermediate pore blocking model and the combined model fit the data well. As permeate flux approached and passed the threshold flux, the combined model was required for accurate fits. Based on this observation, a physical interpretation of the threshold flux is proposed: the threshold flux is the flux below which cake buildup is negligible and above which cake filtration becomes the dominant fouling mechanism

Empirical Investigation Of Determinant Factors Of Company Delisting: Evidence From Indonesia

The main purpose of the research is to evaluate determinant factors which contribute to companies being delisted from Stock Exchange Market in Indonesia. The samples are taken from the delisted companies list in IDX for a period year 2007-2011. The matching companies are then selected based on the company size to make an equivalent comparison for each delisted companies sample. The total final samples consist of 58 companies, 29 delisted companies and 29 matching companies. This research analyzes the company's financial status by using descriptive statistics, independent sample t-test, and logistic regression model to find the effect of each determinant to the probability of delisting. The shares liquidity is a significant determinant to company's delisting in Indonesia. Meanwhile, profitability and leverage seems to be determinant factors for delisted, but appear to be insignificant. Other examined factors, market capitalization and growth opportunity appear to insignificant determinants. This manager implication of this research is that the strong delisting factor is the external company factor, in this case, the market factor

Hubungan Antara Persepsi Terhadap Kelompok Referensi Dengan Pengambilan Keputusan Membeli Produk Kosmetika Tanpa Label Halal Pada Mahasiswi Muslim

The aim of the study is to examine the relationship between perceptions of reference group to the decision making to purchase cosmetic products without permitted halal label on woman students. Hypothesis of this study is that there is positive correlation between the perceptions of the reference group to the decision making to purchase cosmetic products without permitted halal label on woman students. The subjects of this study are the woman students of Syari\u27ah and Law Faculty, Sunan Kalijaga Islam State University, which use the cosmetic products without permitted halal label. The data was collected using two scale for it measurement, are the decision making scale to purchase cosmetic products without permitted halal label, refers to the step of purchased decision making stated by Assael (1998), and the perceptions scale to the reference group, based on the theory proposed by Assael (1992). The data analysis method used is Product Moment and Pearson technique, which shows the correlation values of r = 0.369 with p = 0.000. It means that the relationship between the perceptions of reference group with the decision making to purchase cosmetic products without permitted halal label on woman students are very significant. Therefore, the hypothesis is accepted. Positive perceptions of the reference group gives effective contribution to the decision making to purchase cosmetic products with permitted halal label as big as 13,6%. Keywords: positive perception, reference group, decision making to purchase, cosmetics product without halal label

Polarization memory in single Quantum Dots

We measured the polarization memory of excitonic and biexcitonic optical transitions from single quantum dots at either positive, negative or neutral charge states. Positive, negative and no circular or linear polarization memory was observed for various spectral lines, under the same quasi-resonant excitation below the wetting layer band-gap. We developed a model which explains both qualitatively and quantitatively the experimentally measured polarization spectrum for all these optical transitions. We consider quite generally the loss of spin orientation of the photogenerated electron-hole pair during their relaxation towards the many-carrier ground states. Our analysis unambiguously demonstrates that while electrons maintain their initial spin polarization to a large degree, holes completely dephase.Comment: 6 pages, 4 figure

Excitation spectroscopy of single quantum dots at tunable positive, neutral and negative charge states

We present a comprehensive study of the optical transitions and selection rules of variably charged single self-assembled InAs/GaAs quantum dots. We apply high resolution polarization sensitive photoluminescence excitation spectroscopy to the same quantum dot for three different charge states: neutral and negatively or positively charged by one additional electron or hole. From the detailed analysis of the excitation spectra, a full understanding of the single-carrier energy levels and the interactions between carriers in these levels is extracted for the first time.Comment: 8 pages, 5 figure