235 research outputs found
Exact phase shifts for atom interferometry
In the case of an external Hamiltonian at most quadratic in position and
momentum operators, we use the ABCD formulation of atom optics to establish an
exact analytical phase shift expression for atom interferometers with arbitrary
spatial or temporal beam splitter configurations. This result is expressed in
terms of coordinates and momenta of the wave packet centers at the interaction
vertices only.Comment: 11 pages, 3 figures, submitted to Phys. Lett.
The theory of quantum levitators
We develop a unified theory for clocks and gravimeters using the
interferences of multiple atomic waves put in levitation by traveling light
pulses. Inspired by optical methods, we exhibit a propagation invariant, which
enables to derive analytically the wave function of the sample scattering on
the light pulse sequence. A complete characterization of the device sensitivity
with respect to frequency or to acceleration measurements is obtained. These
results agree with previous numerical simulations and confirm the conjecture of
sensitivity improvement through multiple atomic wave interferences. A realistic
experimental implementation for such clock architecture is discussed.Comment: 11 pages, 6 Figures. Minor typos corrected. Final versio
Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline
compound has been measured as function of temperature and magnetic field up to
14T. It is found that the application of an external magnetic field suppresses
the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic
field dependence reveals a negative magnetocapacitance which is proportional to
the magnetic susceptibility, suggesting a common magnetostrictive origin for
the magnetic field dependence of the two quantities. This result is very
different from that obtained from the isostructural compound Ni3V2O8 that
presents a peak in the dielectric constant at the incommensurate magnetic phase
transition coupled to a sign change of the magnetocapacitance
Long-Term Stability of an Area-Reversible Atom-Interferometer Sagnac Gyroscope
We report on a study of the long-term stability and absolute accuracy of an
atom interferometer gyroscope. This study included the implementation of an
electro-optical technique to reverse the vector area of the interferometer for
reduced systematics and a careful study of systematic phase shifts. Our data
strongly suggests that drifts less than 96 deg/hr are possible after
empirically removing shifts due to measured changes in temperature, laser
intensity, and several other experimental parameters.Comment: 4 pages, 4 figures, submitted to PR
Is it possible to detect gravitational waves with atom interferometers?
We investigate the possibility to use atom interferometers to detect
gravitational waves. We discuss the interaction of gravitational waves with an
atom interferometer and analyze possible schemes
The interlayer cohesive energy of graphite from thermal desorption of polyaromatic hydrocarbons
We have studied the interaction of polyaromatic hydrocarbons (PAHs) with the
basal plane of graphite using thermal desorption spectroscopy. Desorption
kinetics of benzene, naphthalene, coronene and ovalene at sub-monolayer
coverages yield activation energies of 0.50 eV, 0.85 eV, 1.40 eV and 2.1 eV,
respectively. Benzene and naphthalene follow simple first order desorption
kinetics while coronene and ovalene exhibit fractional order kinetics owing to
the stability of 2-D adsorbate islands up to the desorption temperature.
Pre-exponential frequency factors are found to be in the range
- as obtained from both Falconer--Madix (isothermal
desorption) analysis and Antoine's fit to vapour pressure data. The resulting
binding energy per carbon atom of the PAH is 5 meV and can be identified
with the interlayer cohesive energy of graphite. The resulting cleavage energy
of graphite is ~meV/atom which is considerably larger than previously
reported experimental values.Comment: 8 pages, 4 figures, 2 table
Colobanthus quitensis (h.b.k.) bartl. (caryophyllaceae) en los andes colombianos
Colobantbus quitensis y Deschampsia antarctica son las dos únicas fanerogamas nativas presentes hoy dia en el continente antártico (Green, 1970). La primera tiene una distribución amplia en regiones templadas y frías de América Latina, desde la Tierra del Fuego hasta México (Moore, 1972). En noviembre de 1978 se realizó una exploración geobotánica corta al Páramo Alto del Almorzadero en la Cordillera Oriental, Departamento de Santander; en el piso pantanoso de un vallecito a 3.900 m (El Tutal) se encontraron algunas maticas dispersas de Colobanthus quitensis (biótipo laxa) cerca de una corriente lenta de agua. El hallazgo anterior de Colobanthus quitensis en la región del Nevado del Ruiz en la Cordillera Central motivó la elaboración del presente trabajo, con el fin de dar a conocer los caracteres morfológicos, palinológicos y sociológicos de esta interesante especie
Spectra of soft ring graphs
We discuss of a ring-shaped soft quantum wire modeled by interaction
supported by the ring of a generally nonconstant coupling strength. We derive
condition which determines the discrete spectrum of such systems, and analyze
the dependence of eigenvalues and eigenfunctions on the coupling and ring
geometry. In particular, we illustrate that a random component in the coupling
leads to a localization. The discrete spectrum is investigated also in the
situation when the ring is placed into a homogeneous magnetic field or threaded
by an Aharonov-Bohm flux and the system exhibits persistent currents.Comment: LaTeX 2e, 17 pages, with 10 ps figure
Precision Measurement of the Newtonian Gravitational Constant Using Cold Atoms
About 300 experiments have tried to determine the value of the Newtonian
gravitational constant, G, so far, but large discrepancies in the results have
made it impossible to know its value precisely. The weakness of the
gravitational interaction and the impossibility of shielding the effects of
gravity make it very difficult to measure G while keeping systematic effects
under control. Most previous experiments performed were based on the torsion
pendulum or torsion balance scheme as in the experiment by Cavendish in 1798,
and in all cases macroscopic masses were used. Here we report the precise
determination of G using laser-cooled atoms and quantum interferometry. We
obtain the value G=6.67191(99) x 10^(-11) m^3 kg^(-1) s^(-2) with a relative
uncertainty of 150 parts per million (the combined standard uncertainty is
given in parentheses). Our value differs by 1.5 combined standard deviations
from the current recommended value of the Committee on Data for Science and
Technology. A conceptually different experiment such as ours helps to identify
the systematic errors that have proved elusive in previous experiments, thus
improving the confidence in the value of G. There is no definitive relationship
between G and the other fundamental constants, and there is no theoretical
prediction for its value, against which to test experimental results. Improving
the precision with which we know G has not only a pure metrological interest,
but is also important because of the key role that G has in theories of
gravitation, cosmology, particle physics and astrophysics and in geophysical
models.Comment: 3 figures, 1 tabl
Probing host pathogen cross-talk by transcriptional profiling of both Mycobacterium tuberculosis and infected human dendritic cells and macrophages
This study provides the proof of principle that probing the host and the microbe transcriptomes simultaneously is a valuable means to accessing unique information on host pathogen interactions. Our results also underline the extraordinary plasticity of host cell and pathogen responses to infection, and provide a solid framework to further understand the complex mechanisms involved in immunity to M. tuberculosis and in mycobacterial adaptation to different intracellular environments
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