Alternative method for reconstruction of antihydrogen annihilation vertices

The ALPHA experiment, located at CERN, aims to compare the properties of antihydrogen atoms with those of hydrogen atoms. The neutral antihydrogen atoms are trapped using an octupole magnetic trap. The trap region is surrounded by a three layered silicon detector used to reconstruct the antiproton annihilation vertices. This paper describes a method we have devised that can be used for reconstructing annihilation vertices with a good resolution and is more efficient than the standard method currently used for the same purpose.     

Antihydrogen formation by autoresonant excitation of antiproton plasmas

In efforts to trap antihydrogen, a key problem is the vast disparity between the neutral trap energy scale ( $\sim\!50\,\upmu\mathrm{eV}$ ), and the energy scales associated with plasma confinement and space charge (~1 eV). In order to merge charged particle species for direct recombination, the larger energy scale must be overcome in a manner that minimizes the initial antihydrogen kinetic energy. This issue motivated the development of a novel injection technique utilizing the inherent nonlinear nature of particle oscillations in our traps. We demonstrated controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm or tenuous plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination. The nature of this injection overcomes some of the difficulties associated with matching the energies of the charged species used to produce antihydrogen.     

Weak and strong wall boundary procedures and convergence to steady-state of the Navier–Stokes equations

We study the influence of different implementations of no-slip solid wall boundary conditions on the convergence to steady-state of the Navier–Stokes equations. The various approaches are investigated using the energy method and an eigenvalue analysis. It is shown that the weak implementation is superior and enhances the convergence to steady-state for coarse meshes. It is also demonstrated that all the stable approaches produce the same convergence rate as the mesh size goes to zero. The numerical results obtained by using a fully nonlinear finite volume solver support the theoretical findings from the linear analysis.     

Single-shot measurement of triplet-singlet relaxation in a Si/SiGe double quantum dot

We investigate the lifetime of two-electron spin states in a few-electron Si/SiGe double dot. At the transition between the (1,1) and (0,2) charge occupations, Pauli spin blockade provides a readout mechanism for the spin state. We use the statistics of repeated single-shot measurements to extract the lifetimes of multiple states simultaneously. When the magnetic field is zero, we find that all three triplet states have equal lifetimes, as expected, and this time is ~10 ms. When the field is nonzero, the T(0) lifetime is unchanged, whereas the T- lifetime increases monotonically with the field, reaching 3 sec at 1 T.     

ChemInform Abstract: Novel Electronic Configuration in ∂-Pu.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Vibrational transitions in Rydberg matter clusters from stimulated Raman and Rabi‐flopping phase delay in the infrared

Recently, rotational spectra of giant Rydberg matter (RM) clusters were studied in the radio frequency range (Mol. Phys. 105 (2007) 933–939), giving high‐precision bond distances in the nanometer range. However, the theoretical and experimental problem of vibrational motion or, rather, coupled electronic‐vibrational motion in the RM clusters is still unsolved; but it is expected that broad phonon bands will exist. Spectroscopic signatures from space make it likely that RM is a common form of matter in the Universe, and phonon bands in this spectroscopic range have not been taken into account so far. Spectroscopic results are now reported on transitions in the range 0.01–20 cm⁻¹, using primarily infrared (IR) lasers to probe the RM in a tunable open cavity with a Fabry–Perot interferometer to aid in the identification of the shifts. Stimulated Raman scattering from electronic transitions and Rabi‐flopping from electronic states in the clusters are observed. The broad stimulated Raman peaks are assigned to one and two consecutive vibrational (electronic‐vibrational) transitions. Theoretical values predicted for vibrations (phonon maxima) and electronic processes are in reasonable agreement with the experimental results. Improved calculations are needed to verify the assignments of the vibrational phonon distributions. Copyright © 2008 John Wiley & Sons, Ltd.