Error-resistant Single Qubit Gates with Trapped Ions

Coherent operations constitutive for the implementation of single and multi-qubit quantum gates with trapped ions are demonstrated that are robust against variations in experimental parameters and intrinsically indeterministic system parameters. In particular, pulses developed using optimal control theory are demonstrated for the first time with trapped ions. Their performance as a function of error parameters is systematically investigated and compared to composite pulses.Comment: 5 pages 5 figure

Study of ambiguities in π−p→ΛK0\pi^-p\to \Lambda K^0 scattering amplitudes

Amplitudes for the reaction $\pi^-p\to \Lambda K^0$ are reconstructed from data on the differential cross section $d\sigma/d\Omega$, the recoil polarization $P$, and on the spin rotation parameter $\beta$. At low energies, no data on $\beta$ exist, resulting in ambiguities. An approximation using $S$ and $P$ waves leads only to a fair description of the data on $d\sigma/d\Omega$ and $P$; in this case, there are two sets of amplitudes. Including $D$ waves, the data on $d\sigma/d\Omega$ and $P$ are well reproduced by the fit but now, there are several distinct solutions which describe the data with identical precision. In the range where the spin rotation parameter $\beta$ was measured, a full and unambiguous reconstruction of the partial wave amplitudes is possible. The energy-independent amplitudes are compared to the energy dependent amplitudes which resulted from a coupled channel fit (BnGa2011-02) to a large data set including both pion and photo-induced reactions. Significant deviations are observed. Consistency between energy dependent and energy independent solutions by choosing the energy independent solution which is closest to the energy dependent solution. In a second step, the {\it known} energy dependent solution for low (or high) partial waves is imposed and only the high (or low) partial waves are fitted leading to smaller uncertainties

Spider biodiversity patterns and their conservation in the Azorean archipelago, with descriptions of new species

Copyright © 2008 The Natural History Museum.In this contribution, we report on patterns of spider species diversity of the Azores, based on recently standardised sampling protocols in different habitats of this geologically young and isolated volcanic archipelago. A total of 122 species is investigated, including eight new species, eight new records for the Azorean islands and 61 previously known species, with 131 new records for individual islands. Biodiversity patterns are investigated, namely patterns of range size distribution for endemics and non‐endemics, habitat distribution patterns, island similarity in species composition and the estimation of species richness for the Azores. Newly described species are: Oonopidae ‐ Orchestina furcillata Wunderlich; Linyphiidae: Linyphiinae ‐ Porrhomma borgesi Wunderlich; Turinyphia cavernicola Wunderlich; Linyphiidae: Micronetinae ‐Agyneta depigmentata Wunderlich; Linyphiidae: Erigoninae ‐ Acorigone gen. nov. with its type species Acorigone zebraneus Wunderlich; Clubionidae ‐ Cheiracanthium floresense Wunderlich; Cheiracanthium jorgeense Wunderlich; Salticidae ‐ Neon acoreensis Wunderlich. Other major taxonomic changes are: Diplocentria acoreensis Wunderlich, 1992 (Linyphiidae) is transferred to Acorigone (comb. nov.), Leucognatha Wunderlich 1995 (Tetragnathidae) is not an endemic genus of the Azores but an African taxon and synonymous with Sancus Tullgren, 1910; Leucognatha acoreensis Wunderlich, 1992 is transferred to Sancus. Minicia picoensis Wunderlich, 1992 is a synonym of M. floresensis Wunderlich, 1992. For each species additional information is presented about its known distribution in the islands, its colonisation status, habitat occurrence and biogeographical origin

Simultaneous cooling of axial vibrational modes in a linear ion trap

In order to use a collection of trapped ions for experiments where a well-defined preparation of vibrational states is necessary, all vibrational modes have to be cooled to ensure precise and repeatable manipulation of the ions quantum states. A method for simultaneous sideband cooling of all axial vibrational modes is proposed. By application of a magnetic field gradient the absorption spectrum of each ion is modified such that sideband resonances of different vibrational modes coincide. The ion string is then irradiated with monochromatic electromagnetic radiation, in the optical or microwave regime, for sideband excitation. This cooling scheme is investigated in detailed numerical studies. Its application for initializing ion strings for quantum information processing is extensively discussed

Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio Source Populations

We present the first results from a study of the radio continuum properties of galaxies in the 2dF Galaxy Redshift Survey, based on thirty 2dF fields covering a total area of about 100 square degrees. About 1.5% of galaxies with b(J) < 19.4 mag are detected as radio continuum sources in the NRAO VLA Sky Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are active galaxies (mostly low-power radio galaxies and a few Seyferts). The combination of 2dFGRS and NVSS will eventually yield a homogeneous set of around 4000 radio-galaxy spectra, which will be a powerful tool for studying the distriibution and evolution of both AGN and starburst galaxies out to redshift z=0.3.Comment: 14 pages, 7 figures, accepted for publication in PAS

Fast optical control of spin in semiconductor interfacial structures

We report on a picosecond-fast optical removal of spin polarization from a self-confined photo-carrier system at an undoped GaAs/AlGaAs interface possessing superior long-range and high-speed spin transport properties. We employed a modified resonant spin amplification technique with unequal intensities of subsequent pump pulses to experimentally distinguish the evolution of spin populations originating from different excitation laser pulses. We demonstrate that the density of spins, which is injected into the system by means of the optical orientation, can be controlled by reducing the electrostatic confinement of the system using an additional generation of photocarriers. It is also shown that the disturbed confinement recovers within hundreds of picoseconds after which spins can be again photo-injected into the system