Numerical modeling of the central spin problem using the spin-coherent-state representation

In this work, we consider decoherence of a central spin by a spin bath. In order to study the nonperturbative decoherence regimes, we develop an efficient mean-field-based method for modeling the spin-bath decoherence, based on the representation of the central spin density matrix. The method can be applied to longitudinal and transverse relaxation at different external fields. In particular, by modeling large-size quantum systems (up to 16 000 bath spins), we make controlled predictions for the slow long-time decoherence of the central spin.     

Hydrogen bonding: Part 19. IR and NMR study of the lower hydrates of choline fluoride and acetylcholine chloride

Acetylcholine chloride, like choline chloride, forms a liquid salt dihydrate, and a crystalline monohydrate that only exists at reduced pressure; at atmospheric pressure the monohydrate disproportionates into liquid dihydrate and anhydrous acetylcholine chloride. Both choline and acetylcholine chlorides give endothermic dissolution in water. In contrast, choline fluoride gives exothermic dissclution in water, and forms an extra-ordinarily stable monohydrate in which choline cation hydroxyls form strong hydrogen bonds to an H₄O₂F^2?₂ cluster anion. Since the hydration behavior of choline fluoride is like that of unsubstituted tetraalkylammonium fluorides, the unusual hydration behavior of choline and acetyline chlorides results from the presence of chloride ion, and is not an intrinsic property of cholinergic cations.     

Quantitative liquid chromatography of metal tetraalkyls

A method is presented for determining the concentrations of transition metal tetraalkyls in alkane solutions by liquid chromatography. Data for standard solutions of tetranorbornylchromium and tetranorbornyltitanium demonstrate that concentrations are determined with an average error of 2–4%. The method is particularly useful in the determination of disappearance quantum yields for the metal alkyls.     

Mechanisms of decoherence in weakly anisotropic molecular magnets

Decoherence mechanisms in crystals of weakly anisotropic magnetic molecules, such as V15, are studied. We show that an important decohering factor is the rapid thermal fluctuation of dipolar interactions between magnetic molecules. A model is proposed to describe the influence of this source of decoherence. Based on the exact solution of this model, we show that at relatively high temperatures, about 0.5 K, the quantum coherence in a V15 molecule is not suppressed and, in principle, can be detected experimentally. Therefore, these molecules may be suitable prototype systems for study of physical processes taking place in quantum computers.     

The electronic structure of Lu

The electronic structure of hcp Lu has been calculated using a linearized augmented plane wave (LAPW) method and the Hedin-Lundqvist local density approximation for exchange and correlation. Although complete self-consistency was hindered by the proximity of the 4f levels to the Fermi energy, the valence bands were converged and the calculation yielded a Fermi surface remarkably similar to that calculated by Keeton and Loucks. Comparison is made with recent de Haas-van Alphen and neutron magnetic form factor experiments.     

Temperature dependence of the c-axis phonon dispersion curves of hcp Zr

The temperature dependence of the vibrational modes of hcp Zr, between 6 and 1007K, were studied by inelastic neutron scattering techniques. As the temperature decreases we observe a rather large increase in the frequencies of all but the [001] L0 branch. The zone center mode of the [001] L0 branch softens appreciably and at 6K this branch exhibits a dip at the zone center reminiscent of the anomalous dispersion observed in technetium.