70 research outputs found

    Near-unity coupling efficiency of a quantum emitter to a photonic-crystal waveguide

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    A quantum emitter efficiently coupled to a nanophotonic waveguide constitutes a promising system for the realization of single-photon transistors, quantum-logic gates based on giant single-photon nonlinearities, and high bit-rate deterministic single-photon sources. The key figure of merit for such devices is the β\beta-factor, which is the probability for an emitted single photon to be channeled into a desired waveguide mode. We report on the experimental achievement of β=98.43±0.04%\beta = 98.43 \pm 0.04\% for a quantum dot coupled to a photonic-crystal waveguide, corresponding to a single-emitter cooperativity of η=62.7±1.5\eta = 62.7 \pm 1.5. This constitutes a nearly ideal photon-matter interface where the quantum dot acts effectively as a 1D "artificial" atom, since it interacts almost exclusively with just a single propagating optical mode. The β\beta-factor is found to be remarkably robust to variations in position and emission wavelength of the quantum dots. Our work demonstrates the extraordinary potential of photonic-crystal waveguides for highly efficient single-photon generation and on-chip photon-photon interaction

    Single-photon nonlinear optics with a quantum dot in a waveguide

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    Strong nonlinear interactions between photons enable logic operations for both classical and quantum-information technology. Unfortunately, nonlinear interactions are usually feeble and therefore all-optical logic gates tend to be inefficient. A quantum emitter deterministically coupled to a propagating mode fundamentally changes the situation, since each photon inevitably interacts with the emitter, and highly correlated many-photon states may be created . Here we show that a single quantum dot in a photonic-crystal waveguide can be utilized as a giant nonlinearity sensitive at the single-photon level. The nonlinear response is revealed from the intensity and quantum statistics of the scattered photons, and contains contributions from an entangled photon-photon bound state. The quantum nonlinearity will find immediate applications for deterministic Bell-state measurements and single-photon transistors and paves the way to scalable waveguide-based photonic quantum-computing architectures

    Double-heterostructure cavities: from theory to design

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    We derive a frequency-domain-based approach for radiation (FAR) from double-heterostructure cavity (DHC) modes. We use this to compute the quality factors and radiation patterns of DHC modes. The semi-analytic nature of our method enables us to provide a general relationship between the radiation pattern of the cavity and its geometry. We use this to provide general designs for ultrahigh quality factor DHCs with radiation patterns that are engineered to emit vertically

    Homocysteine, vitamin B12 and folate levels in premature coronary artery disease

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    BACKGROUND: Hyperhomocysteinemia is known as an independent risk factor of atherosclerosis, but the probable role of hyperhomocysteinemia in premature Coronary Artery Disease (CAD) is not well studied. The aim of this study was to assess the role of hyperhomocysteinemia, folate and Vitamin B12 deficiency in the development of premature CAD. METHODS: We performed an analytical case-control study on 294 individuals under 45 years (225 males and 69 females) who were admitted for selective coronary angiography to two centers in Tehran. RESULTS: After considering the exclusion criteria, a total number of 225 individuals were enrolled of which 43.1% had CAD. The mean age of participants was 39.9 +/- 4.3 years (40.1 +/- 4.2 years in males and 39.4 +/- 4.8 years in females). Compared to the control group, the level of homocysteine measured in the plasma of the male participants was significantly high (14.9 +/- 1.2 versus 20.3 +/- 1.9 micromol/lit, P = 0.01). However there was no significant difference in homocysteine level of females with and without CAD (11.8 +/- 1.3 versus 11.5 ± 1.1 micromol/lit, P = 0.87). Mean plasma level of folic acid and vitamin B12 in the study group were 6.3 +/- 0.2 and 282.5 +/- 9.1 respectively. Based on these findings, 10.7% of the study group had folate deficiency while 26.6% had Vitamin B12 deficiency. Logistic regression analysis for evaluating independent CAD risk factors showed hyperhomocysteinemia as an independent risk factor for premature CAD in males (OR = 2.54 0.95% CI 1.23 to 5.22, P = 0.01). Study for the underlying causes of hyperhomocysteinemia showed that male gender and Vitamin B12 deficiency had significant influence on incidence of hyperhomocysteinemia. CONCLUSION: We may conclude that hyperhomocysteinemia is an independent risk factor for CAD in young patients (bellow 45 years old) – especially in men -and vitamin B12 deficiency is a preventable cause of hyperhomocysteinemia

    Assessment of Sialic Acid distribution in mouse epididymis

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    Previous studies have shown that epididymial and its secretions are critical for sperm maturation. These secretions contain many glycoconjugates with sialic acid terminal sugar. This terminal sugar by intervening in cellular interactions and masking surface receptors, has an important role in sperm maturation and protection. Moreover lectins have been employed as useful probes to detect the presence of glycoconjugates with specific sugar residues such as sialic acid. Considering the importance of sialic acid, distribution of this terminal sugar in different parts of mouse epididymis was studied by means of lectin histochemistry. For this purpose, epididymial tissue species were obtained from 15 adult male BALB/c mice. After fixation and routine laboratory process, 5 µm sections prepared from paraffin blocks. Slides were exposed to lectins with lectin-histochemistry. For this purpose, wheat germ agglutinin (WGA), specific for sialic acid, was employed. Then they assessed with light microscope. The rate of reactions in epithelial cells and spermatozoa were significantly different parts of epididyms. In this manner that, in spermatozoa, stereo cilia and luminal surface the least reactions were seen in caput, while the most reactions were seen in cauda. Epithelial cells, too, showed less reaction in caput comparing to corpus and tail of epididyms. Sialic acid has been identified in many glycoproteins secreted by epididyms and is necessary for sperm maturation. It seems that this maturation happens mostly in body and tail of epididyms during epididymial transit. Increase in sialic acid content of spermatozoa during epididymial transit is probably due to the secretion of glycoconjugates containing this component by epididymial principal and flask cells. Keywords: Epididymis, Sialic acid, Lectin histochemistry, Mous
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