373 research outputs found
Quasi-1D Bose-Einstein condensates in the dimensional crossover regime
We study theoretically the dimensional crossover from a three-dimensional
elongated condensate to a one-dimensional condensate as the transverse degrees
of freedom get frozen by tight confinement, in the limit of small density
fluctuations, i.e. for a strongly degenerate gas. We compute analytically the
radially integrated density profile at low temperatures using a local density
approximation, and study the behavior of phase fluctuations with the transverse
confinement. Previous studies of phase fluctuations in trapped gases have
either focused on the 3D elongated regimes or on the 1D regime. The present
approach recovers these previous results and is able to interpolate between
them. We show in particular that in this strongly degenerate limit the shape of
the spatial correlation function is insensitive to the transverse regime of
confinement, pointing out to an almost universal behavior of phase fluctuations
in elongated traps
Measurement of the Gravity-Field Curvature by Atom Interferometry
We present the first direct measurement of the gravity-field curvature based
on three conjugated atom interferometers. Three atomic clouds launched in the
vertical direction are simultaneously interrogated by the same atom
interferometry sequence and used to probe the gravity field at three equally
spaced positions. The vertical component of the gravity-field curvature
generated by nearby source masses is measured from the difference between
adjacent gravity gradient values. Curvature measurements are of interest in
geodesy studies and for the validation of gravitational models of the
surrounding environment. The possibility of using such a scheme for a new
determination of the Newtonian constant of gravity is also discussed.Comment: 5 pages, 3 figure
Determination of the Newtonian Gravitational Constant Using Atom Interferometry
We present a new measurement of the Newtonian gravitational constant G based
on cold atom interferometry. Freely falling samples of laser-cooled rubidium
atoms are used in a gravity gradiometer to probe the field generated by nearby
source masses. In addition to its potential sensitivity, this method is
intriguing as gravity is explored by a quantum system. We report a value of
G=6.667 10^{-11} m^{3} kg^{-1} s^{-2}, estimating a statistical uncertainty of
0.011 10^{-11} m^{3} kg^{-1} s^{-2} and a systematic uncertainty of
0.003 10^{-11} m^{3} kg^{-1} s^{-2}. The long-term stability of the instrument
and the signal-to-noise ratio demonstrated here open interesting perspectives
for pushing the measurement accuracy below the 100 ppm level.Comment: 4 figure
Sensitivity limits of a Raman atom interferometer as a gravity gradiometer
We evaluate the sensitivity of a dual cloud atom interferometer to the
measurement of vertical gravity gradient. We study the influence of most
relevant experimental parameters on noise and long-term drifts. Results are
also applied to the case of doubly differential measurements of the
gravitational signal from local source masses. We achieve a short term
sensitivity of 3*10^(-9) g/Hz^(-1/2) to differential gravity acceleration,
limited by the quantum projection noise of the instrument. Active control of
the most critical parameters allows to reach a resolution of 5*10^(-11) g after
8000 s on the measurement of differential gravity acceleration. The long term
stability is compatible with a measurement of the gravitational constant G at
the level of 10^(-4) after an integration time of about 100 hours.Comment: 19 pages, 20 figure
Quantum test of the equivalence principle for atoms in superpositions of internal energy eigenstates
The Einstein Equivalence Principle (EEP) has a central role in the
understanding of gravity and space-time. In its weak form, or Weak Equivalence
Principle (WEP), it directly implies equivalence between inertial and
gravitational mass. Verifying this principle in a regime where the relevant
properties of the test body must be described by quantum theory has profound
implications. Here we report on a novel WEP test for atoms. A Bragg atom
interferometer in a gravity gradiometer configuration compares the free fall of
rubidium atoms prepared in two hyperfine states and in their coherent
superposition. The use of the superposition state allows testing genuine
quantum aspects of EEP with no classical analogue, which have remained
completely unexplored so far. In addition, we measure the Eotvos ratio of atoms
in two hyperfine levels with relative uncertainty in the low ,
improving previous results by almost two orders of magnitude.Comment: Accepted for publication in Nature Communicatio
Second Order Correlation Function of a Phase Fluctuating Bose-Einstein Condensate
The coherence properties of phase fluctuating Bose-Einstein condensates are
studied both theoretically and experimentally. We derive a general expression
for the N-particle correlation function of a condensed Bose gas in a highly
elongated trapping potential. The second order correlation function is analyzed
in detail and an interferometric method to directly measure it is discussed and
experimentally implemented. Using a Bragg diffraction interferometer, we
measure intensity correlations in the interference pattern generated by two
spatially displaced copies of a parent condensate. Our experiment demonstrates
how to characterize the second order correlation function of a highly elongated
condensate and to measure its phase coherence length.Comment: 22 pages, 5 figure
Atom Interferometry with the Rb Blue Transitions
We demonstrate a novel scheme for Raman-pulse and Bragg-pulse atom
interferometry based on the blue transitions of
Rb that provides an increase by a factor of the interferometer
phase due to accelerations with respect to the commonly used infrared
transition at 780 nm. A narrow-linewidth laser system generating more than 1 W
of light in the 420-422 nm range was developed for this purpose. Used as a
cold-atom gravity gradiometer, our Raman interferometer attains a stability to
differential acceleration measurements of at 1 s and
after 2000 s of integration time. When operated on
first-order Bragg transitions, the interferometer shows a stability of
g at 1 s, averaging to g after 2000 s of
integration time. The instrument sensitivity, currently limited by the noise
due to spontaneous emission, can be further improved by increasing the laser
power and the detuning from the atomic resonance. The present scheme is
attractive for high-precision experiments as, in particular, for the
determination of the Newtonian gravitational constant
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