Laser Cooling of 85Rb Atoms to the Recoil Temperature Limit

We demonstrate the laser cooling of 85Rb atoms in a two-dimensional optical lattice. We follow the two-step degenerate Raman sideband cooling scheme [Kerman et al., Phys. Rev. Lett. 84, 439 (2000)], where a fast cooling of atoms to an auxiliary state is followed by a slow cooling to a dark state. This method has the advantage of independent control of the heating rate and cooling rate from the optical pumping beam. We operate the lattice at a Lamb-Dicke parameter eta=0.45 and show the cooling of spin-polarized 85Rb atoms to the recoil temperature in both dimension within 2.4 ms with the aid of adiabatic cooling

Influence of the Coriolis force in atom interferometry

In a light-pulse atom interferometer, we use a tip-tilt mirror to remove the influence of the Coriolis force from Earth's rotation and to characterize configuration space wave packets. For interferometers with large momentum transfer and large pulse separation time, we improve the contrast by up to 350% and suppress systematic effects. We also reach what is to our knowledge the largest spacetime area enclosed in any atom interferometer to date. We discuss implications for future high performance instruments.Comment: 4 pages, 5 figures, 1 tabl

Controlled Heterogeneous Nucleation and Growth of Germanium Quantum Dots on Nanopatterned Silicon Dioxide and Silicon Nitride Substrates

Controlled heterogeneous nucleation and growth of Ge quantum dots (QDs) are demonstrated on SiO_2/Si_3N_4 substrates by means of a novel fabrication process of thermally oxidizing nanopatterned SiGe layers. The otherwise random self-assembly process for QDs is shown to be strongly influenced by the nanopatterning in determining both the location and size of the QDs. Ostwald ripening processes are observed under further annealing at the oxidation temperature. Both nanopattern oxidation and Ostwald ripening offer additional mechanisms for lithography for controlling the size and placement of the QDs

High-resolution atom interferometers with suppressed diffraction phases

We experimentally and theoretically study the diffraction phase of large-momentum transfer beam splitters in atom interferometers based on Bragg diffraction. We null the diffraction phase and increase the sensitivity of the interferometer by combining Bragg diffraction with Bloch oscillations. We demonstrate agreement between experiment and theory, and a 1500-fold reduction of the diffraction phase, limited by measurement noise. In addition to reduced systematic effects, our interferometer has high contrast with up to 4.4 million radians of phase difference, and a resolution in the fine structure constant of $\delta \alpha/\alpha=0.25\,$ppb in 25 hours of integration time.Comment: Added appendix and explanations. 6 pages, 4 figure

Stationary Light Pulses in Cold Atomic Media

Stationary light pulses (SLPs), i.e., light pulses without motion, are formed via the retrieval of stored probe pulses with two counter-propagating coupling fields. We show that there exist non-negligible hybrid Raman excitations in media of cold atoms that prohibit the SLP formation. We experimentally demonstrate a method to suppress these Raman excitations and realize SLPs in laser-cooled atoms. Our work opens the way to SLP studies in cold as well as in stationary atoms and provides a new avenue to low-light-level nonlinear optics.Comment: 4 pages, 4 figure

Integrating before and after crash features into measuring the effectiveness of intersection safety improvement project in Harbin /

Many studies focused on the analysis of effect factors contributing to the crashes and development of crash prediction models have resulted in aggregate researches to quantify the safety effects of geometric and traffic variables and environmental concerns on the expected outcome of fatal, injury and/or property damage losses at specific locations. Crash insight regarding different locations, however, has rarely been performed. Such investigations are useful for at least two reasons. First, there is a priori need to identify high risk sites with respect to crash. Second, it is generally believed that different crash types (e.g. rear-end, angle etc.) are associated with road geometry, the environment and traffic condition, and as a result justifying the inside causes of such crashes helps with understanding and improving the specific ability to make effective countermeasures. Therefore, the objectives of this paper are to (1) demonstrate that different crash types are associated to intersections in different ways and (2) reveal that the statistics of intersection crashes may lead to greater insights considering crash occurrence and countermeasure effectiveness. This paper first divides crashes into 5 categories or types: pedestrian-involved, rear-end, head-on, angle and sideswipe crash types. Based on 3208 crashes collected on the intersections in the city of Harbin during the period of 1992–2008, distribution, overall count and the occurrence of rate features are estimated resulting in two models. The performed analysis reveals that safety improvement factors such as the presence of a signal light set, a traffic monitoring device and ITS measure have a positive association with intersection crash in different ways, suggesting that different traffic control and management aspects may be helpful in identifying specific countermeasures in the overall safety improvement project. Santrauka Daugelis tyrimų, nagrinėjančių efektyvumo veiksnius, padedančius nustatyti susidūrimų prognozavimo modelius, paskatino įvairius tyrimus įvertinti eismo aplinkos sudedamųjų dalių ir jų parametrų įtaką mirties ir (arba) turtinės žalos atvejams konkrečiose vietose. Iki šiol tai buvo retas reiškinys. Tokie tyrimai yra svarbūs bent jau dėl dviejų priežasčių. Pirma, reikia nustatyti padidintos rizikos vietas atsižvelgiant į eismo įvykį. Antra, manoma, kad skirtingos susidūrimo rūšys yra susijusios su kelio geometrija, aplinkos ir eismo sąlygomis ir kaip pasekmė, pateisinanti vidines tokių susidūrimų priežastis, padeda suprasti ir pagerinti konkrečias galimybes imtis atsakomųjų veiksmų. Todėl šio darbo tikslas—parodyti, kad skirtingos susidūrimo rūšys įvairiai susijusios su eismu sankryžose, kad susidūrimų sankryžose statistika gali lemti didesnę įžvalgą, atsižvelgiant į įvykusį eismo įvykį ir atsakomųjų priemonių veiksmingumą. Šiame darbe susidūrimai skirstomi į 5 rūšis: susidūrimai su pėsčiaisiais, įvažiavimas į galinę transporto priemonės dalį, susidūrimas priekinėmis transporto priemonės dalimis, kampinis smūgis ir šoninis smūgis. Pasiskirstymas, bendras skaičius ir susidūrimų dažnis apskaičiuojami pagal du modelius remiantis informacija, surinkta iš 3028 eismo įvykių, įvykusių 1992–2008 m. Charbino miesto (Kinija) sankryžose. Atlikta analizė parodė, kad saugaus gerinimo veiksniai, t. y. šviesoforas, eismo stebėjimo prietaisai ir t.t., turi teigiamą įtaką. Skirtingi eismo kontrolės ir valdymo aspektai gali padėti rasti konkrečias atsakomąsias priemones, įgyvendinant visą saugaus eismo gerinimo projektą. Резюме Проблема безопасности дорожного движения актуальна во всех городах мира. Не является исключением и китайский город Харбин. Авторы исследуют влияние совокупности факторов, возникающих до и после дорожно-транспортного происшествия, для оценки эффективности проекта по безопасному движению на перекрестках в упомянутом городе. Исследуются места увеличенного риска возникновения дорожно-транспортного происшествия. Также принимается во внимание, что различные типы дорожно-транспортных происшествий тесно связаны с геометрическими параметрами дороги, условиями окружающей среды, условиями самого движения и т. д. Целью исследования было показать связь и влияние различных типов дорожно-транспортных происшествий на конкретные ситуации движения на перекрестках. Это необходимо для того, чтобы понять необходимость ответных мер по обеспечению безопасности дорожного движения в потенциально опасных местах. Все дорожно-транспортные происшествия разделены на 5 типов. Далее на основании информации о 3028 дорожно-транспортных происшествий, зарегистрированных в период с 1992 по 2008 гг. на перекрестках города Харбина, представлены статистические результаты исследования. Проведенное исследование показало, что меры по увеличению безопасности дорожного движения (например, светофор, видео наблюдение за движением и т. д.) имели положительное влияние. Различные аспекты контроля за дорожным движением и управления им помогают найти ответные меры по претворению в жизнь проекта по обеспечению безопасности дорожного движения. Reikšminiai žodžiai: susidūrimas, sankryža, susidūrimų dažnis, eismo kontrolė, šviesos signalas, atsakomosios priemonės, saugus eismas Ключевые слова: дорожно-транспортное происшествие, безопасность дорожного движения, перекресток, столкновение, контроль за движением, ответные мер