871 research outputs found
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
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
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
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
Metastable Feshbach Molecules in High Rotational States
We experimentally demonstrate Cs2 Feshbach molecules well above the
dissociation threshold, which are stable against spontaneous decay on the
timescale of one second. An optically trapped sample of ultracold dimers is
prepared in an l-wave state and magnetically tuned into a region with negative
binding energy. The metastable character of these molecules arises from the
large centrifugal barrier in combination with negligible coupling to states
with low rotational angular momentum. A sharp onset of dissociation with
increasing magnetic field is mediated by a crossing with a g-wave dimer state
and facilitates dissociation on demand with a well defined energy.Comment: 4 pages, 5 figure
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
Dark resonances as a probe for the motional state of a single ion
Single, rf-trapped ions find various applications ranging from metrology to
quantum computation. High-resolution interrogation of an extremely weak
transition under best observation conditions requires an ion almost at rest. To
avoid line-broadening effects such as the second order Doppler effect or rf
heating in the absence of laser cooling, excess micromotion has to be
eliminated as far as possible. In this work the motional state of a confined
three-level ion is probed, taking advantage of the high sensitivity of observed
dark resonances to the trapped ion's velocity. Excess micromotion is controlled
by monitoring the dark resonance contrast with varying laser beam geometry. The
influence of different parameters such as the cooling laser intensity has been
investigated experimentally and numerically
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