841 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
Search for free-floating planetary-mass objects in the Pleiades
(Abridged) We aim at identifying the least massive population of the solar
metallicity, young (120 Myr), nearby (133.5 pc) Pleiades star cluster with the
ultimate goal of understanding the physical properties of intermediate-age,
free-floating, low-mass brown dwarfs and giant planetary-mass objects, and
deriving the cluster substellar mass function across the deuterium-burning mass
limit at ~0.012 Msol. We performed a deep photometric and astrometric J- and
H-band survey covering an area of ~0.8 deg^2. The images with completeness and
limiting magnitudes of J,H ~ 20.2 and ~ 21.5 mag were acquired ~9 yr apart
(proper motion precision of +/-6 mas/yr). J- and H-band data were complemented
with Z, K, and mid-infrared magnitudes up to 4.6 micron coming from UKIDSS,
WISE, and follow-up observations of our own. Pleiades member candidates were
selected to have proper motions compatible with that of the cluster, and colors
following the known Pleiades sequence in the interval J = 15.5-8.8 mag, and
Z_UKIDSS - J > 2.3 mag or Z nondetections for J > 18.8 mag. We found a neat
sequence of astrometric and photometric Pleiades substellar member candidates
in the intervals J = 15.5-21.2 mag and ~0.072-0.008 Msol. The faintest objects
show very red near- and mid-infrared colors exceeding those of field
high-gravity dwarfs by >0.5 mag. The Pleiades photometric sequence does not
show any color turn-over because of the presence of photospheric methane
absorption down to J = 20.3 mag, which is about 1 mag fainter than predicted by
the color-computed models. Pleiades brown dwarfs have a proper motion
dispersion of 6.4-7.5 mas/yr and are dynamically relaxed at the age of the
cluster. The Pleiades mass function extends down to the deuterium burning-mass
threshold, with a slope fairly similar to that of other young star clusters and
stellar associations.Comment: Accepted for publication in A&A. 16 page
Implementation of quantum gates and preparation of entangled states in cavity QED with cold trapped ions
We propose a scheme to perform basic gates of quantum computing and prepare
entangled states in a system with cold trapped ions located in a single mode
optical cavity. General quantum computing can be made with both motional state
of the trapped ion and cavity state being qubits. We can also generate
different kinds of entangled states in such a system without state reduction,
and can transfer quantum states from the ion in one trap to the ion in another
trap. Experimental requirement for achieving our scheme is discussed.Comment: To appear in J. Opt.
The Randomized Shortened Dental Arch Study: Tooth Loss
The evidence concerning the management of shortened dental arch (SDA) cases is sparse. This multi-center study was aimed at generating data on outcomes and survival rates for two common treatments, removable dental prostheses (RDP) for molar replacement or no replacement (SDA). The hypothesis was that the treatments lead to different incidences of tooth loss. We included 215 patients with complete molar loss in one jaw. Molars were either replaced by RDP or not replaced, according to the SDA concept. First tooth loss after treatment was the primary outcome measure. This event occurred in 13 patients in the RDP group and nine patients in the SDA group. The respective Kaplan-Meier survival rates at 38 months were 0.83 (95% CI: 0.74-0.91) in the RDP group and 0.86 (95% CI: 0.78-0.95) in the SDA group, the difference being non-significant
The Stability of Radiatively Cooled Jets in Three Dimensions
The effect of optically thin radiative cooling on the Kelvin-Helmholtz
instability of three dimensional jets is investigated via linear stability
theory and nonlinear hydrodynamical simulation. Two different cooling functions
are considered: radiative cooling is found to have a significant effect on the
stability of the jet in each case. The wavelengths and growth rates of unstable
modes in the numerical simulations are found to be in good agreement with
theoretical predictions. Disruption of the jet is found to be sensitive to the
precessional frequency at the origin with lower frequencies leading to more
rapid disruption. Strong nonlinear effects are observed as the result of the
large number of normal modes in three dimensions which provide rich mode-mode
interactions. These mode-mode interactions provide new mechanisms for the
formation of knots in the flows. Significant structural features found in the
numerical simulations appear similar to structures observed on protostellar
jets.Comment: 32 pages, 13 figures, figures included in page tota
Three-Dimensional Simulations of Jets from Keplerian Disks: Self--Regulatory Stability
We present the extension of previous two-dimensional simulations of the
time-dependent evolution of non-relativistic outflows from the surface of
Keplerian accretion disks, to three dimensions. The accretion disk itself is
taken to provide a set of fixed boundary conditions for the problem. The 3-D
results are consistent with the theory of steady, axisymmetric, centrifugally
driven disk winds up to the Alfv\'en surface of the outflow. Beyond the
Alfv\'en surface however, the jet in 3-D becomes unstable to non-axisymmetric,
Kelvin-Helmholtz instabilities. We show that jets maintain their long-term
stability through a self-limiting process wherein the average Alfv\'enic Mach
number within the jet is maintained to order unity. This is accomplished in at
least two ways. First, poloidal magnetic field is concentrated along the
central axis of the jet forming a ``backbone'' in which the Alfv\'en speed is
sufficiently high to reduce the average jet Alfv\'enic Mach number to unity.
Second, the onset of higher order Kelvin-Helmholtz ``flute'' modes (m \ge 2)
reduce the efficiency with which the jet material is accelerated, and transfer
kinetic energy of the outflow into the stretched, poloidal field lines of the
distorted jet. This too has the effect of increasing the Alfv\'en speed, and
thus reducing the Alfv\'enic Mach number. The jet is able to survive the onset
of the more destructive m=1 mode in this way. Our simulations also show that
jets can acquire corkscrew, or wobbling types of geometries in this relatively
stable end-state, depending on the nature of the perturbations upon them.
Finally, we suggest that jets go into alternating periods of low and high
activity as the disappearance of unstable modes in the sub-Alfv\'enic regime
enables another cycle of acceleration to super-Alfv\'enic speeds.Comment: 57 pages, 22 figures, submitted to Ap
Vacuum-field level shifts in a single trapped ion mediated by a single distant mirror
A distant mirror leads to a vacuum-induced level shift in a laser-excited
atom. This effect has been measured with a single mirror 25 cm away from a
single, trapped barium ion. This dispersive action is the counterpart to the
mirror's dissipative effect, which has been shown earlier to effect a change in
the ion's spontaneous decay [J. Eschner et al., Nature 413, 495-498 (2001)].
The experimental data are well described by 8-level optical Bloch equations
which are amended to take into account the presence of the mirror according to
the model in [U. Dorner and P. Zoller, Phys. Rev. A 66, 023816 (2002)].
Observed deviations from simple dispersive behavior are attributed to
multi-level effects.Comment: version accepted by PR
Prevalence Rates of Mental Disorders in Chilean Prisons
PMCID: PMC371883
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