224 research outputs found
Experiments towards quantum information with trapped Calcium ions
Ground state cooling and coherent manipulation of ions in an rf-(Paul) trap
is the prerequisite for quantum information experiments with trapped ions. With
resolved sideband cooling on the optical S1/2 - D5/2 quadrupole transition we
have cooled one and two 40Ca+ ions to the ground state of vibration with up to
99.9% probability. With a novel cooling scheme utilizing electromagnetically
induced transparency on the S1/2 - P1/2 manifold we have achieved simultaneous
ground state cooling of two motional sidebands 1.7 MHz apart. Starting from the
motional ground state we have demonstrated coherent quantum state manipulation
on the S1/2 - D5/2 quadrupole transition at 729 nm. Up to 30 Rabi oscillations
within 1.4 ms have been observed in the motional ground state and in the n=1
Fock state. In the linear quadrupole rf-trap with 700 kHz trap frequency along
the symmetry axis (2 MHz in radial direction) the minimum ion spacing is more
than 5 micron for up to 4 ions. We are able to cool two ions to the ground
state in the trap and individually address the ions with laser pulses through a
special optical addressing channel.Comment: Proceedings of the ICAP 2000, Firenz
Coupling a single atomic quantum bit to a high finesse optical cavity
The quadrupole S -- D optical transition of a single trapped
Ca ion, well suited for encoding a quantum bit of information, is
coherently coupled to the standing wave field of a high finesse cavity. The
coupling is verified by observing the ion's response to both spatial and
temporal variations of the intracavity field. We also achieve deterministic
coupling of the cavity mode to the ion's vibrational state by selectively
exciting vibrational state-changing transitions and by controlling the position
of the ion in the standing wave field with nanometer-precision
Precision measurement and compensation of optical Stark shifts for an ion-trap quantum processor
Using optical Ramsey interferometry, we precisely measure the laser-induced
AC-stark shift on the -- "quantum bit" transition near 729
nm in a single trapped Ca ion. We cancel this shift using an
additional laser field. This technique is of particular importance for the
implementation of quantum information processing with cold trapped ions. As a
simple application we measure the atomic phase evolution during a rotation of the quantum bit.Comment: 4 pages, 4 figure
Quantum interference from remotely trapped ions
We observe quantum interference of photons emitted by two continuously
laser-excited single ions, independently trapped in distinct vacuum vessels.
High contrast two-photon interference is observed in two experiments with
different ion species, calcium and barium. Our experimental findings are
quantitatively reproduced by Bloch equation calculations. In particular, we
show that the coherence of the individual resonance fluorescence light field is
determined from the observed interference
Ground state cooling, quantum state engineering and study of decoherence of ions in Paul traps
We investigate single ions of in Paul traps for quantum
information processing. Superpositions of the S electronic ground state
and the metastable D state are used to implement a qubit. Laser light
on the S D transition is used for the
manipulation of the ion's quantum state. We apply sideband cooling to the ion
and reach the ground state of vibration with up to 99.9% probability. Starting
from this Fock state , we demonstrate coherent quantum state
manipulation. A large number of Rabi oscillations and a ms-coherence time is
observed. Motional heating is measured to be as low as one vibrational quantum
in 190 ms. We also report on ground state cooling of two ions.Comment: 12 pages, 6 figures. submitted to Journal of Modern Optics, Special
Issue on Quantum Optics: Kuehtai 200
Laser ablation loading of a surface-electrode ion trap
We demonstrate loading by laser ablation of Sr ions into a
mm-scale surface-electrode ion trap. The laser used for ablation is a pulsed,
frequency-tripled Nd:YAG with pulse energies of 1-10 mJ and durations of 3-5
ns. An additional laser is not required to photoionize the ablated material.
The efficiency and lifetime of several candidate materials for the laser
ablation target are characterized by measuring the trapped ion fluorescence
signal for a number of consecutive loads. Additionally, laser ablation is used
to load traps with a trap depth (40 meV) below where electron impact ionization
loading is typically successful ( 500 meV).Comment: 4 pages, 4 figure
All-optical ion generation for ion trap loading
We have investigated the all-optical generation of ions by photo-ionisation
of atoms generated by pulsed laser ablation. A direct comparison between a
resistively heated oven source and pulsed laser ablation is reported. Pulsed
laser ablation with 10 ns Nd:YAG laser pulses is shown to produce large calcium
flux, corresponding to atomic beams produced with oven temperatures greater
than 650 K. For an equivalent atomic flux, pulsed laser ablation is shown to
produce a thermal load more than one order of magnitude smaller than the oven
source. The atomic beam distributions obey Maxwell-Boltzmann statistics with
most probable speeds corresponding to temperatures greater than 2200 K. Below a
threshold pulse fluence between 280 mJ/cm^2 and 330 mJ/cm^2, the atomic beam is
composed exclusively of ground state atoms. For higher fluences ions and
excited atoms are generated.Comment: 7 pages, 9 figure
Vertical profile of peroxyacetyl nitrate (PAN) from MIPAS-STR measurements over Brazil in February 2005 and its contribution to tropical UT NOy partitioning
We report on the retrieval of PAN (CH<sub>3</sub>C(O)OONO<sub>2</sub>) in the upper tropical troposphere from limb measurements by the remote-sensor MIPAS-STR on board the Russian high altitude research aircraft M55-Geophysica. The measurements were performed close to Araçatuba, Brazil, on 17 February 2005. The retrieval was made in the spectral range 775–820 cm<sup>−1</sup> where PAN exhibits its strongest feature but also more than 10 species interfere. Especially trace gases such as CH<sub>3</sub>CCl<sub>3</sub>, CFC-113, CFC-11, and CFC-22, emitting also in spectrally broad not-resolved branches, make the processing of PAN prone to errors. Therefore, the selection of appropriate spectral windows, the separate retrieval of several interfering species and the careful handling of the water vapour profile are part of the study presented. <br><br> The retrieved profile of PAN has a maximum of about 0.14 ppbv at 10 km altitude, slightly larger than the lowest reported values (<0.1 ppbv) and much lower than the highest reported in the literature (0.65 ppbv). Besides the NO<sub>y</sub> constituents measured by MIPAS-STR (HNO<sub>3</sub>, ClONO<sub>2</sub>, HO<sub>2</sub>NO<sub>2</sub>, PAN), the in situ instruments aboard the Geophysica provide simultaneous measurements of NO, NO<sub>2</sub>, and the sum NO<sub>y</sub>. Comparing the sum of in-situ and remotely derived NO+NO<sub>2</sub>+HNO<sub>3</sub>+ClONO<sub>2</sub>+HO<sub>2</sub>NO<sub>2</sub>+PAN with total NO<sub>y</sub> a deficit of 30–40% (0.2–0.3 ppbv) in the troposphere remains unexplained whereas the values fit well in the stratosphere
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