Test of the isotopic and velocity selectivity of a lithium atom interferometer by magnetic dephasing

A magnetic field gradient applied to an atom interferometer induces a $M$-dependent phase shift which results in a series of decays and revivals of the fringe visibility. Using our lithium atom interferometer based on Bragg laser diffraction, we have measured the fringe visibility as a function of the applied gradient. We have thus tested the isotopic selectivity of the interferometer, the velocity selective character of Bragg diffraction for different diffraction orders as well as the effect of optical pumping of the incoming atoms. All these observations are qualitatively understood but a quantitative analysis requires a complete model of the interferometer

Lithium atom interferometer using laser diffraction : description and experiments

We have built and operated an atom interferometer of the Mach-Zehnder type. The atomic wave is a supersonic beam of lithium seeded in argon and the mirrors and beam-splitters for the atomic wave are based on elastic Bragg diffraction on laser standing waves at 671 nm. We give here a detailed description of our experimental setup and of the procedures used to align its components. We then present experimental signals, exhibiting atomic interference effects with a very high visibility, up to 84.5 %. We describe a series of experiments testing the sensitivity of the fringe visibility to the main alignment defects and to the magnetic field gradient.Comment: 8 avril 200

Mach-Zehnder Bragg interferometer for a Bose-Einstein Condensate

We construct a Mach-Zehnder interferometer using Bose-Einstein condensed rubidium atoms and optical Bragg diffraction. In contrast to interferometers based on normal diffraction, where only a small percentage of the atoms contribute to the signal, our Bragg diffraction interferometer uses all the condensate atoms. The condensate coherence properties and high phase-space density result in an interference pattern of nearly 100% contrast. In principle, the enclosed area of the interferometer may be arbitrarily large, making it an ideal tool that could be used in the detection of vortices, or possibly even gravitational waves.Comment: 10 pages, 3 figures, Quantum Electronics and Laser Science Conference 1999, Postdeadline papers QPD12-

Diffraction of complex molecules by structures made of light

We demonstrate that structures made of light can be used to coherently control the motion of complex molecules. In particular, we show diffraction of the fullerenes C60 and C70 at a thin grating based on a standing light wave. We prove experimentally that the principles of this effect, well known from atom optics, can be successfully extended to massive and large molecules which are internally in a thermodynamic mixed state and which do not exhibit narrow optical resonances. Our results will be important for the observation of quantum interference with even larger and more complex objects.Comment: 4 pages, 3 figure

The Effect of Feedback Medium on Accuracy with English Articles

Developing and demonstrating English proficiency is a critical skill for non-native English speakers (NNESs) who wish to study in American universities. Unlike their native English speaker (NES) counterparts, NNES students who apply for university admission are required to demonstrate their proficiency in English via tests, such as the Test of English as a Foreign Language (TOEFL), that measure an NNES\u27s ability to understand, speak, read, and write English. Although the number of students who have attained those minimum scores is large, there is a large population of adult NNESs enrolled in intensive English programs (IEPs) that are designed to help them improve their proficiency in English and again admission into mainstream university courses. Given that many university instructors require the submission of written work that demonstrates students\u27 understanding of course content, perhaps the most important academic skill developed in IEPs is writing. Furthermore, the lack of attention given to addressing grammatical errors at the tertiary level highlights IEP instructors\u27 need for effective and efficient methods of addressing grammatical errors in NNES writing. The present quantitative study used two experimental designs, a pretest-posttest design and a posttest-only design with proxy pretest (Campbell & Stanley, 1963), to investigate the efficacy of two types of indirect corrective feedback (CF) for improving adult, IEP-enrolled, intermediate level NNES writers\u27 (participants) grammatical accuracy in academic papers. Grammatical accuracy for this study was measured by counting the number of errors participants committed when using English definite and indefinite articles in academic papers. The independent variable for this study was the type of CF participants were randomly selected to receive – either screencast corrective feedback (SCF) or written corrective feedback (WCF). The dependent variable, which measured the effect of the CF given, was the number of errors participants made with English definite and indefinite articles on three compositions completed to satisfy the requirements of their IEP writing class. The results of the current research demonstrated that participants made similar gains in grammatical accuracy when using CF to revise descriptive compositions. These results are in keeping with the results of previous studies that showed the usefulness of CF for improving grammatical accuracy on revised compositions (Bitchener, 2008, Bitchener & Knoch, 2008, 2009a, 2009b, 2010a). However, the improvement observed on the revised descriptive compositions did not transfer to new classification essays, regardless of the type of CF participants received. Participants\u27 lack of grammatical accuracy on new compositions of a different genre effectively illustrated the difficulty English articles pose for NNESs when writing and the need for multiple exposures to CF and writing practice to develop NNESs\u27 ability to consistently use English articles accurately. The main implication of the present study lies in the recommendation of the provision of CF to NNES students and systematic instruction about how to use CF received in order to allow NNESs to become more self-sufficient learners and writers of English

A new photon recoil experiment: towards a determination of the fine structure constant

We report on progress towards a measurement of the fine structure constant to an accuracy of $5\times 10^{-10}$ or better by measuring the ratio of the Planck constant to the mass of the cesium atom. Compared to similar experiments, ours is improved in three significant ways: (i) simultaneous conjugate interferometers, (ii) multi-photon Bragg diffraction between same internal states, and (iii) an about 1000 fold reduction of laser phase noise to -138 dBc/Hz. Combining that with a new method to simultaneously stabilize the phases of four frequencies, we achieve 0.2 mrad effective phase noise at the location of the atoms. In addition, we use active stabilization to suppress systematic effects due to beam misalignment.Comment: 12 pages, 9 figure

Potential mechanisms maintaining a conspicuous polymorphism in eastern mosquitofish (Gambusia holbrooki)

Genetic variation often precedes adaptation, so the mechanisms that maintain this variation are a central topic in evolutionary biology. Gambusia holbrooki, or eastern mosquitofish, possesses a rare polymorphism for melanistic coloration. Melanics and typical silver males were examined for differences in behavioral and physiological traits that may impact the persistence of the melanism trait. No differences in standard metabolic rate were found via closed-chamber respirometry, but a detour task indicated that melanic males possess greater cognitive flexibility. Effects of the social environment on stress and reproductive traits were also evaluated by pairing males and comparing cortisol levels and sperm quality to individual baselines. These controlled social pairings revealed no significant relationships between social factors, stress, and reproductive traits. Future work may better illustrate the role of environmental factors on the persistence of melanism by thoroughly characterizing both competitive and reproductive interactions and evaluating potential physiological mechanisms underlying differences in cognition

Environmental DNA Analysis of a Critically Endangered Cavefish

https://louis.uah.edu/research-horizons/1313/thumbnail.jp