186 research outputs found
High contrast Mach-Zehnder lithium atom interferometer in the Bragg regime
We have constructed an atom interferometer of the Mach-Zehnder type,
operating with a supersonic beam of lithium. Atom diffraction uses Bragg
diffraction on laser standing waves. With first order diffraction, our
apparatus has given a large signal and a very good fringe contrast (74%), which
we believe to be the highest ever observed with atom interferometers. This
apparatus will be applied to high sensitivity measurementsComment: 6 pages, 3 figures, accepted by Appl. Phys.
Correcting symmetry imperfections in linear multipole traps
Multipole radio-frequency traps are central to collisional experiments in
cryogenic environments. They also offer possibilities to generate new type of
ion crystals topologies and in particular the potential to create infinite
1D/2D structures: ion rings and ion tubes. However, multipole traps have also
been shown to be very sensitive to geometrical misalignment of the trap rods,
leading to additional local trapping minima. The present work proposes a method
to correct non-ideal potentials, by modifying the applied radio-frequency
amplitudes for each trap rod. This approach is discussed for the octupole trap,
leading to the restitution of the ideal Mexican-Hat-like pseudo-potential,
expected in multipole traps. The goodness of the compensation method is
quantified in terms of the choice of the diagnosis area, the residual trapping
potential variations, the required adaptation of the applied radio-frequency
voltage amplitudes, and the impact on the trapped ion structures. Experimental
implementation for macroscopic multipole traps is also discussed, in order to
propose a diagnostic method with respect to the resolution and stability of the
trap drive. Using the proposed compensation technique, we discuss the
feasibility of generating a homogeneous ion ring crystal, which is a measure of
quality for the obtained potential well
Fast accumulation of ions in a dual trap
Transporting charged particles between different traps has become an
important feature in high-precision spectroscopy experiments of different
types. In many experiments in atomic and molecular physics, the optical probing
of the ions is not carried out at the same location as the creation or state
preparation. In our double linear radio-frequency trap, we have implemented a
fast protocol allowing to shuttle large ion clouds very efficiently between
traps, in times shorter than a millisecond. Moreover, our shuttling protocol is
a one-way process, allowing to add ions to an existing cloud without loss of
the already trapped sample. This feature makes accumulation possible, resulting
in the creation of large ion clouds. Experimental results show, that ion clouds
of large size are reached with laser-cooling, however, the described mechanism
does not rely on any cooling process
Doppler cooling of calcium ions using a dipole-forbidden transition
Doppler cooling of calcium ions has been experimentally demonstrated using
the S1/2 to D5/2 dipole-forbidden transition. Scattering forces and
fluorescence levels a factor of 5 smaller than for usual Doppler cooling on the
dipole allowed S1/2 to P1/2 transition have been achieved. Since the light
scattered from the ions can be monitored at (violet) wavelengths that are very
different from the excitation wavelengths, single ions can be detected with an
essentially zero background level. This, as well as other features of the
cooling scheme, can be extremely valuable for ion trap based quantum
information processing.Comment: 4 pages, 4 figures, minor changes to commentary and reference
Two-step Doppler cooling of a three-level ladder system with an intermediate metastable level
Doppler laser cooling of a three-level ladder system using two near-resonant
laser fields is analyzed in the case of the intermediate level being metastable
while the upper level is short-lived. Analytical as well as numerical results
for e.g. obtainable scattering rates and achievable temperatures are presented.
When appropriate, comparisons with two-level single photon Doppler laser
cooling is made. These results are relevant to recent experimental Doppler
laser cooling investigations addressing intercombination lines in alkali-earth
metal atoms and quadrupole transitions in alkali-earth metal ions.Comment: accepted by Phys Rev
Parallel ion strings in linear multipole traps
Additional radio-frequency (rf) potentials applied to linear multipole traps
create extra field nodes in the radial plane which allow one to confine single
ions, or strings of ions, in totally rf field-free regions. The number of nodes
depends on the order of the applied multipole potentials and their relative
distance can be easily tuned by the amplitude variation of the applied
voltages. Simulations using molecular dynamics show that strings of ions can be
laser cooled down to the Doppler limit in all directions of space. Once cooled,
organized systems can be moved with very limited heating, even if the cooling
process is turned off
Structural phase transitions in multipole traps
A small number of laser-cooled ions trapped in a linear radiofrequency
multipole trap forms a hollow tube structure. We have studied, by means of
molecular dynamics simulations, the structural transition from a double ring to
a single ring of ions. We show that the single-ring configuration has the
advantage to inhibit the thermal transfer from the rf-excited radial components
of the motion to the axial component, allowing to reach the Doppler limit
temperature along the direction of the trap axis. Once cooled in this
particular configuration, the ions experience an angular dependency of the
confinement if the local adiabaticity parameter exceeds the empirical limit.
Bunching of the ion structures can then be observed and an analytic expression
is proposed to take into account for this behaviour
Anharmonic contributions in real RF linear quadrupole traps
See also erratum at : http://www.sciencedirect.com/science/article/pii/S1387380610001004International audienceThe radiofrequency quadrupole linear ion trap is a widely used device in physics and chemistry. When used for trapping of large ion clouds, the presence of anharmonic terms in the radiofrequency potential limits the total number of stored ions. In this paper, we have studied the anharmonic content of the trapping potential for different implementations of a quadrupole trap, searching for the geometry best suited for the trapping of large ion clouds. This is done by calculating the potential of a real trap using SIMION8.0, followed by a fit, which allows us to obtain the evolution of anharmonic terms for a large part of the inner volume of the trap
About the dynamics and thermodynamics of trapped ions
This tutorial introduces the dynamics of charged particles in a
radiofrequency trap in a very general manner to point out the differences
between the dynamics in a quadrupole and in a multipole trap. When dense
samples are trapped, the dynamics is modified by the Coulomb repulsion between
ions. To take into account this repulsion, we propose to use a method,
originally developed for particles in Penning trap, that model the ion cloud as
a cold fluid. This method can not reproduce the organisation of cold clouds as
crystals but it allows one to scale the size of large samples with the trapping
parameters and the number of ions trapped, for different linear geometries of
trap.Comment: accepted for publication in the "Modern Applications of Trapped Ions"
special issu
Evaluation of the ultimate performances of a Ca+ single-ion frequency standard
We numerically evaluate the expected performances of an optical frequency
standard at 729 nm based on a single calcium ion. The frequency stability is
studied through the Allan deviation and its dependence on the excitation method
(single Rabi pulse or two Ramsey pulses schemes) and the laser linewidth are
discussed. The minimum Allan deviation that can be expected is estimated to
with the
integration time. The frequency shifts induced by the environmental conditions
are evaluated to minimize the uncertainty of the proposed standard by chosing
the most suited environment for the ion. If using the odd isotope
Ca and a vessel cooled to 77 K, the expected relative shift is with an uncertainty of , mainly due to
the quadrupole shift induced by the unknown static electric field gradient .Comment: soumis le 27/07/04 a Physics Letters
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