412 research outputs found
Space-time sensors using multiple-wave atom levitation
The best clocks to date control the atomic motion by trapping the sample in
an optical lattice and then interrogate the atomic transition by shining on
these atoms a distinct laser of controlled frequency. In order to perform both
tasks simultaneously and with the same laser field, we propose to use instead
the levitation of a Bose-Einstein condensate through multiple-wave atomic
interferences. The levitating condensate experiences a coherent localization in
momentum and a controlled diffusion in altitude. The sample levitation is bound
to resonance conditions used either for frequency or for acceleration
measurements. The chosen vertical geometry solves the limitations imposed by
the sample free fall in previous optical clocks using also atomic
interferences. This configuration yields multiple-wave interferences enabling
levitation and enhancing the measurement sensitivity. This setup, analogous to
an atomic resonator in momentum space, constitutes an attractive alternative to
existing atomic clocks and gravimeters.Comment: 5 pages, 4 figures.Final versio
Reforming the international system of units: On our way to redefine the base units solely from fundamental constants and beyond
Our purpose is to offer a logical analysis of the system of units and to
explore possible paths towards a consistent and unified system with an original
perspective. The path taken here builds on the fact that, thanks to optical or
matter-wave interferometry, any measurement can be reduced to a dimensionless
phase measurement and we follow this simple guiding line. We finally show how
one could progress even further on the path of a synthetic framework for
fundamental metrology based upon pure geometry in five dimensions
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
6-axis inertial sensor using cold-atom interferometry
We have developed an atom interferometer providing a full inertial base. This
device uses two counter-propagating cold-atom clouds that are launched in
strongly curved parabolic trajectories. Three single Raman beam pairs, pulsed
in time, are successively applied in three orthogonal directions leading to the
measurement of the three axis of rotation and acceleration. In this purpose, we
introduce a new atom gyroscope using a butterfly geometry. We discuss the
present sensitivity and the possible improvements.Comment: submitted to PR
Does an atom interferometer test the gravitational redshift at the Compton frequency ?
Atom interferometers allow the measurement of the acceleration of freely
falling atoms with respect to an experimental platform at rest on Earth's
surface. Such experiments have been used to test the universality of free fall
by comparing the acceleration of the atoms to that of a classical freely
falling object. In a recent paper, M\"uller, Peters and Chu [Nature {\bf 463},
926-929 (2010)] argued that atom interferometers also provide a very accurate
test of the gravitational redshift when considering the atom as a clock
operating at the Compton frequency associated with the rest mass. We analyze
this claim in the frame of general relativity and of different alternative
theories. We show that the difference of "Compton phases" between the two paths
of the interferometer is actually zero in a large class of theories, including
general relativity, all metric theories of gravity, most non-metric theories
and most theoretical frameworks used to interpret the violations of the
equivalence principle. Therefore, in most plausible theoretical frameworks,
there is no redshift effect and atom interferometers only test the universality
of free fall. We also show that frameworks in which atom interferometers would
test the redshift pose serious problems, such as (i) violation of the Schiff
conjecture, (ii) violation of the Feynman path integral formulation of quantum
mechanics and of the principle of least action for matter waves, (iii)
violation of energy conservation, and more generally (iv) violation of the
particle-wave duality in quantum mechanics. Standard quantum mechanics is no
longer valid in such frameworks, so that a consistent interpretation of the
experiment would require an alternative formulation of quantum mechanics. As
such an alternative has not been proposed to date, we conclude that the
interpretation of atom interferometers as testing the gravitational redshift is
unsound.Comment: 26 pages. Modified version to appear in Classical and Quantum Gravit
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
THE "FREELY" FALLING TWO-LEVEL ATOM IN A RUNNING LASER WAVE
The time evolution of a two-level atom which is simultaneously exposed to the
field of a running laser wave and a homogeneous gravitational field is studied.
The result of the coupled dynamics of internal transitions and center-of-mass
motion is worked out exactly. Neglecting spontaneous emission and performing
the rotating wave approximation we derive the complete time evolution operator
in an algebraical way by using commutation relations. The result is discussed
with respect to the physical implications. In particular the long time and
short time behaviour is physically analyzed in detail. The breakdown of the
Magnus perturbation expansion is shown.Comment: 14 Pages, Late
Progress towards an accurate determination of the Boltzmann constant by Doppler spectroscopy
In this paper, we present significant progress performed on an experiment
dedicated to the determination of the Boltzmann constant, k, by accurately
measuring the Doppler absorption profile of a line in a gas of ammonia at
thermal equilibrium. This optical method based on the first principles of
statistical mechanics is an alternative to the acoustical method which has led
to the unique determination of k published by the CODATA with a relative
accuracy of 1.7 ppm. We report on the first measurement of the Boltzmann
constant by laser spectroscopy with a statistical uncertainty below 10 ppm,
more specifically 6.4 ppm. This progress results from improvements in the
detection method and in the statistical treatment of the data. In addition, we
have recorded the hyperfine structure of the probed saQ(6,3) rovibrational line
of ammonia by saturation spectroscopy and thus determine very precisely the
induced 4.36 (2) ppm broadening of the absorption linewidth. We also show that,
in our well chosen experimental conditions, saturation effects have a
negligible impact on the linewidth. Finally, we draw the route to future
developments for an absolute determination of with an accuracy of a few ppm.Comment: 22 pages, 11 figure
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