503 research outputs found
Progress in Atomic Fountains at LNE-SYRTE
We give an overview of the work done with the Laboratoire National de
M\'etrologie et d'Essais-Syst\`emes de R\'ef\'erence Temps-Espace (LNE-SYRTE)
fountain ensemble during the last five years. After a description of the clock
ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest
developments, we review recent studies of several systematic frequency shifts.
This includes the distributed cavity phase shift, which we evaluate for the FO1
and FOM fountains, applying the techniques of our recent work on FO2. We also
report calculations of the microwave lensing frequency shift for the three
fountains, review the status of the blackbody radiation shift, and summarize
recent experimental work to control microwave leakage and spurious phase
perturbations. We give current accuracy budgets. We also describe several
applications in time and frequency metrology: fountain comparisons,
calibrations of the international atomic time, secondary representation of the
SI second based on the 87Rb hyperfine frequency, absolute measurements of
optical frequencies, tests of the T2L2 satellite laser link, and review
fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally,
we give a summary of the tests of the PHARAO cold atom space clock performed
using the FOM transportable fountain.Comment: 19 pages, 12 figures, 5 tables, 126 reference
Extended coherence time on the clock transition of optically trapped Rubidium
Optically trapped ensembles are of crucial importance for frequency
measurements and quantum memories, but generally suffer from strong dephasing
due to inhomogeneous density and light shifts. We demonstrate a drastic
increase of the coherence time to 21 s on the magnetic field insensitive clock
transition of Rb-87 by applying the recently discovered spin self-rephasing.
This result confirms the general nature of this new mechanism and thus shows
its applicability in atom clocks and quantum memories. A systematic
investigation of all relevant frequency shifts and noise contributions yields a
stability of 2.4E-11 x tau^(-1/2), where tau is the integration time in
seconds. Based on a set of technical improvements, the presented frequency
standard is predicted to rival the stability of microwave fountain clocks in a
potentially much more compact setup.Comment: 5 pages, 4 figure
Experimenting an optical second with strontium lattice clocks
Progress in realizing the SI second had multiple technological impacts and
enabled to further constraint theoretical models in fundamental physics.
Caesium microwave fountains, realizing best the second according to its current
definition with a relative uncertainty of 2-4x10^(-16), have already been
superseded by atomic clocks referenced to an optical transition, both more
stable and more accurate. Are we ready for a new definition of the second? Here
we present an important step in this direction: our system of five clocks
connects with an unprecedented consistency the optical and the microwave
worlds. For the first time, two state-of-the-art strontium optical lattice
clocks are proven to agree within their accuracy budget, with a total
uncertainty of 1.6x10^(-16). Their comparison with three independent caesium
fountains shows a degree of reproducibility henceforth solely limited at the
level of 3.1x10^(-16) by the best realizations of the microwave-defined second.Comment: 9 pages, 4 figures, 2 table
An Optical Lattice Clock with Spin-polarized 87Sr Atoms
We present a new evaluation of an 87Sr optical lattice clock using spin
polarized atoms. The frequency of the 1S0-3P0 clock transition is found to be
429 228 004 229 873.6 Hz with a fractional accuracy of 2.6 10^{-15}, a value
that is comparable to the frequency difference between the various primary
standards throughout the world. This measurement is in excellent agreement with
a previous one of similar accuracy
Quadrupole Oscillation of a Single-Vortex Condensate: Evidence for Kelvin Modes
We study the two transverse quadrupole modes of a cigar-shaped Bose-Einstein
condensate with a single centered vortex. We show that the counter-rotating
mode is more strongly damped than in the absence of a vortex, whereas the
co-rotating mode is not affected appreciably by the vortex. We interpret this
result as a decay of the counter-rotating quadrupole mode into two excitations
of the vortex line, the so-called Kelvin modes. This is supported by direct
observation of the wiggling vortex line.Comment: 4 pages, 3 figure
Vortex oscillations in confined Bose-Einstein condensate interacting with 1D optical lattice
We study Bose-Einstein condensate of atomic Boson gases trapped in a
composite potential of a harmonic potential and an optical lattice potential.
We found a series of collective excitations that induces localized vortex
oscillations with a characteristic wavelength. The oscillations might be
observed experimentally when radial confinement is tight. We present the
excitation spectra of the vortex oscillation modes and propose a way to
experimentally excite the modes.Comment: 5 pages, 7 figures. Title, abstract and references are update
Vortex lattice of a Bose-Einstein Condensate in a rotating anisotropic trap
We study the vortex lattices in a Bose-Einstein Condensate in a rotating
anisotropic harmonic trap. We first investigate the single particle
wavefunctions obtained by the exact solution of the problem and give simple
expressions for these wavefunctions in the small anisotropy limit. Depending on
the strength of the interactions, a few or a large number of vortices can be
formed. In the limit of many vortices, we calculate the density profile of the
cloud and show that the vortex lattice stays triangular. We also find that the
vortex lattice planes align themselves with the weak axis of the external
potential. For a small number of vortices, we numerically solve the
Gross-Pitaevskii equation and find vortex configurations that are very
different from the vortex configurations in an axisymmetric rotating trap.Comment: 15 pages,4 figure
From Rotating Atomic Rings to Quantum Hall States
Considerable efforts are currently devoted to the preparation of ultracold
neutral atoms in the emblematic strongly correlated quantum Hall regime. The
routes followed so far essentially rely on thermodynamics, i.e. imposing the
proper Hamiltonian and cooling the system towards its ground state. In rapidly
rotating 2D harmonic traps the role of the transverse magnetic field is played
by the angular velocity. For particle numbers significantly larger than unity,
the required angular momentum is very large and it can be obtained only for
spinning frequencies extremely near to the deconfinement limit; consequently,
the required control on experimental parameters turns out to be far too
stringent. Here we propose to follow instead a dynamic path starting from the
gas confined in a rotating ring. The large moment of inertia of the fluid
facilitates the access to states with a large angular momentum, corresponding
to a giant vortex. The initial ring-shaped trapping potential is then
adiabatically transformed into a harmonic confinement, which brings the
interacting atomic gas in the desired quantum Hall regime. We provide clear
numerical evidence that for a relatively broad range of initial angular
frequencies, the giant vortex state is adiabatically connected to the bosonic
Laughlin state, and we discuss the scaling to many particles.Comment: 9 pages, 5 figure
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