A short response-time atomic source for trapped ion experiments

Ion traps are often loaded from atomic beams produced by resistively heated ovens. We demonstrate an atomic oven which has been designed for fast control of the atomic flux density and reproducible construction. We study the limiting time constants of the system and, in tests with $^{40}\textrm{Ca}$, show we can reach the desired level of flux in 12s, with no overshoot. Our results indicate that it may be possible to achieve an even faster response by applying an appropriate one-off heat treatment to the oven before it is used.Comment: 5 pages, 7 figure

Bi-large neutrino mixing and the Cabibbo angle

Recent measurements of the neutrino mixing angles cast doubt on the validity of the so-far popular tri-bimaximal mixing ansatz. We propose a parametrization for the neutrino mixing matrix where the reactor angle seeds the large solar and atmospheric mixing angles, equal to each other in first approximation. We suggest such bi-large mixing pattern as a model building standard, realized when the leading order value of the reactor angle equals the Cabibbo angle.Comment: 4 pages, 2 figs. v2: matches version appearing in Phys.Rev.D, rapid communication

A new source detection algorithm using FDR

The False Discovery Rate (FDR) method has recently been described by Miller et al (2001), along with several examples of astrophysical applications. FDR is a new statistical procedure due to Benjamini and Hochberg (1995) for controlling the fraction of false positives when performing multiple hypothesis testing. The importance of this method to source detection algorithms is immediately clear. To explore the possibilities offered we have developed a new task for performing source detection in radio-telescope images, Sfind 2.0, which implements FDR. We compare Sfind 2.0 with two other source detection and measurement tasks, Imsad and SExtractor, and comment on several issues arising from the nature of the correlation between nearby pixels and the necessary assumption of the null hypothesis. The strong suggestion is made that implementing FDR as a threshold defining method in other existing source-detection tasks is easy and worthwhile. We show that the constraint on the fraction of false detections as specified by FDR holds true even for highly correlated and realistic images. For the detection of true sources, which are complex combinations of source-pixels, this constraint appears to be somewhat less strict. It is still reliable enough, however, for a priori estimates of the fraction of false source detections to be robust and realistic.Comment: 17 pages, 7 figures, accepted for publication by A

The CFH Optical PDCS survey (COP) I: The Data

This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT: Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey data. We describe our photometric and spectroscopic observations with the MOS multi-slit spectrograph at the CFH telescope. A comparison of the photometry from the PDCS (Postman et al. 1996) catalogs and from the new images we have obtained at the CFH telescope shows that the different magnitude systems can be cross-calibrated. After identification between the PDCS catalogues and our new images, we built catalogues with redshift, coordinates and V, I and Rmagnitudes. We have classified the galaxies along the lines of sight into field and structure galaxies using a gap technique (Katgert et al. 1996). In total we have observed 18 significant structures along the 10 lines of sight.Comment: 40 pages, 13 figures, accepted in A

Coherent spin-valley oscillations in silicon

Electron spins in silicon quantum dots are excellent qubits because they have long coherence times, high gate fidelities, and are compatible with advanced semiconductor manufacturing techniques. The valley degree of freedom, which results from the specific character of the Si band structure, is a unique feature of electrons in Si spin qubits. However, the small difference in energy between different valley levels often poses a challenge for quantum computing in Si. Here, we show that the spin-valley coupling in Si, which enables transitions between states with different spin and valley quantum numbers, enables coherent control of electron spins in Si. We demonstrate coherent manipulation of effective single- and two-electron spin states in a Si/SiGe double quantum dot without ac magnetic or electric fields. Our results illustrate that the valley degree of freedom, which is often regarded as an inconvenience, can itself enable quantum manipulation of electron spin states