121 research outputs found
State of the art in the determination of the fine structure constant and the ratio
The fine structure constant and the ratio between
the Planck constant and the unified atomic mass are keystone constants for the
determination of other fundamental physical constants, especially the ones
involved in the framework of the future International System of units. This
paper presents how these two constants, which can be deduced from one another,
are measured. We will present in detail the measurement of
performed by atomic interferometry at the Laboratoire Kastler Brossel in Paris.
This type of measurement also allows a test of the standard model to be carried
out with unparalleled accuracy.Comment: arXiv admin note: text overlap with arXiv:1309.339
Theoretical Analysis of a Large Momentum Beamsplitter using Bloch Oscillations
In this paper, we present the implementation of Bloch oscillations in an
atomic interferometer to increase the separation of the two interfering paths.
A numerical model, in very good agreement with the experiment, is developed.
The contrast of the interferometer and its sensitivity to phase fluctuations
and to intensity fluctuations are also calculated. We demonstrate that the
sensitivity to phase fluctuations can be significantly reduced by using a
suitable arrangement of Bloch oscillations pulses
Ground state energy of the two-dimensional weakly interacting Bose gas: First correction beyond Bogoliubov theory
We consider the grand potential of a two-dimensional weakly
interacting homogeneous Bose gas at zero temperature. Building on a
number-conserving Bogoliubov method for a lattice model in the grand canonical
ensemble, we calculate the next order term as compared to the Bogoliubov
prediction, in a systematic expansion of in powers of the parameter
measuring the weakness of the interaction. Our prediction is in very good
agreement with recent Monte Carlo calculations.Comment: 4 pages, 1 figure, published in Phys. Rev. Let
Observation of a 2D Bose-gas: from thermal to quasi-condensate to superfluid
We present experimental results on a Bose gas in a quasi-2D geometry near the
Berezinskii, Kosterlitz and Thouless (BKT) transition temperature. By measuring
the density profile, \textit{in situ} and after time of flight, and the
coherence length, we identify different states of the gas. In particular, we
observe that the gas develops a bimodal distribution without long range order.
In this state, the gas presents a longer coherence length than the thermal
cloud; it is quasi-condensed but is not superfluid. Experimental evidence
indicates that we observe the superfluid transition (BKT transition).Comment: 5 pages, 6 figure
Atom interferometry based on light pulses : application to the high precision measurement of the ratio h/m and the determination of the fine structure constant
In this paper we present a short overview of atom interferometry based on
light pulses. We discuss different implementations and their applications for
high precision measurements. We will focus on the determination of the ratio
h/m of the Planck constant to an atomic mass. The measurement of this quantity
is performed by combining Bloch oscillations of atoms in a moving optical
lattice with a Ramsey-Bord\'e interferometer
Precise determination of h/m_Rb using Bloch oscillations and atomic interferometry: a mean to deduce the fine structure constant
We use Bloch oscillations to transfer coherently many photon momenta to
atoms. Then we can measure accurately the ratio h/m_Rb and deduce the fine
structure constant alpha. The velocity variation due to the Bloch oscillations
is measured thanks to Raman transitions. In a first experiment, two Raman
pulses are used to select and measure a very narrow velocity class. This method
yields to a value of the fine structure constant alpha^{-1}= 137.035 998 84
(91) with a relative uncertainty of about 6.6 ppb. More recently we use an
atomic interferometer consisting in two pairs of pi/2 pulses. We present here
the first results obtained with this method
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