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

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

Coupling a single atomic quantum bit to a high finesse optical cavity

The quadrupole S$_{1/2}$ -- D$_{5/2}$ 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

Velocity Field Statistics in Star-Forming Regions. I. Centroid Velocity Observations

The probability density functions (pdfs) of molecular line centroid velocity fluctuations and fluctuation differences at different spatial lags are estimated for several nearby molecular clouds with active internal star formation. The data consist of over 75,000 $^{13}$CO line profiles divided among twelve spatially and/or kinematically distinct regions. Although three regions (all in Mon R2) appear nearly Gaussian, the others show strong evidence for non-Gaussian, often nearly exponential, centroid velocity pdfs, possibly with power law contributions in the far tails. Evidence for nearly exponential centroid pdfs in the neutral HI component of the ISM is also presented, based on older optical and radio observations. These results are in contrast to pdfs found in isotropic incompressible turbulence experiments and simulations. Furthermore, no evidence is found for the scaling of difference pdf kurtosis with Reynolds number which is seen in incompressible turbulence, and the spatial distribution of high-amplitude velocity differences shows little indication of the filamentary appearance predicted by decay simulations dominated by vortical interactions. The variation with lag of the difference pdf moments is presented as a constraint on future simulations.Comment: LaTeX, 23 pages, with 15 Figures included separately as gif image files. Refereed/revised version accepted to the Astrophysical Journal. A complete (but much larger) postscript version is available from http://ktaadn.gsfc.nasa.gov/~miesc

Can Protostellar Jets Drive Supersonic Turbulence in Molecular Clouds?

Jets and outflows from young stellar objects are proposed candidates to drive supersonic turbulence in molecular clouds. Here, we present the results from multi-dimensional jet simulations where we investigate in detail the energy and momentum deposition from jets into their surrounding environment and quantify the character of the excited turbulence with velocity probability density functions. Our study include jet--clump interaction, transient jets, and magnetised jets. We find that collimated supersonic jets do not excite supersonic motions far from the vicinity of the jet. Supersonic fluctuations are damped quickly and do not spread into the parent cloud. Instead subsonic, non-compressional modes occupy most of the excited volume. This is a generic feature which can not be fully circumvented by overdense jets or magnetic fields. Nevertheless, jets are able to leave strong imprints in their cloud structure and can disrupt dense clumps. Our results question the ability of collimated jets to sustain supersonic turbulence in molecular clouds.Comment: 33 pages, 18 figures, accepted by ApJ, version with high resolution figures at: http://www.ita.uni-heidelberg.de/~banerjee/publications/jet_paper.pd

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.

Biomarkers in respiratory diseases

The scientific evidence concerning prosthodontic care for the shortened dental arch (SDA) is sparse. This randomized multicenter study aimed to compare two common treatment options: removable partial dental prostheses (RPDPs) for molar replacement vs. no replacement (SDA). One of the hypotheses was that the follow-up treatment differs between patients with RPDPs and patients with SDAs during the 5-year follow-up period. Two hundred and fifteen patients with complete molar loss in one jaw were included in the study. Molars were either replaced by RPDPs or not replaced according to the SDA concept. A mean number of 4.2 (RPDP) and 2.8 (SDA) treatments for biological or technical reasons occurred during the 5-year observation time per patient. Concerning the biological aspect, no significant differences between the groups could be shown, whereas treatment arising from technical reasons was significantly more frequent for the RPDP group. When the severity of treatment was analyzed, a change over time was evident. When, at baseline, only follow-up treatment with minimal effort is required, over time there is a continuous increase to moderate and extensive effort observed for both groups ( Controlled-trials.com number ISRCTN97265367). </jats:p

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

Observational Implications of Precessing Protostellar Discs and Jets

We consider the dynamics of a protostellar disc in a binary system where the disc is misaligned with the orbital plane of the binary, with the aim of determining the observational consequences for such systems. The disc wobbles with a period approximately equal to half the binary's orbital period and precesses on a longer timescale. We determine the characteristic timescale for realignment of the disc with the orbital plane due to dissipation. If the dissipation is determined by a simple isotropic viscosity then we find, in line with previous studies, that the alignment timescale is of order the viscous evolution timescale. However, for typical protostellar disc parameters, if the disc tilt exceeds the opening angle of the disc, then tidally induced shearing within the disc is transonic. In general, hydrodynamic instabilities associated with the internally driven shear result in extra dissipation which is expected to drastically reduce the alignment timescale. For large disc tilts the alignment timescale is then comparable to the precession timescale, while for smaller tilt angles $\delta$, the alignment timescale varies as $(\sin \delta)^{-1}$. We discuss the consequences of the wobbling, precession and rapid realignment for observations of protostellar jets and the implications for binary star formation mechanisms.Comment: MNRAS, in press. 10 pages. Also available at http://www.ast.cam.ac.uk/~mbat