Entangling strings of neutral atoms in 1D atomic pipeline structures

We study a string of neutral atoms with nearest neighbor interaction in a 1D beam splitter configuration, where the longitudinal motion is controlled by a moving optical lattice potential. The dynamics of the atoms crossing the beam splitter maps to a 1D spin model with controllable time dependent parameters, which allows the creation of maximally entangled states of atoms by crossing a quantum phase transition. Furthermore, we show that this system realizes protected quantum memory, and we discuss the implementation of one- and two-qubit gates in this setup.     

Spin wave measurements in the one-dimensional ferromagnet CsNiF3

By inelastic neutron scattering from CsNiF₃ at 4.2 K spin waves in a one-dimensional ferromagnet are found for the first time. The dispersion relation can be described by only nearest neighbour interaction and follows the relation ν = 0.09 + 0.98 [1 ? cos (π_qc)] THz.     

On the mechanism of the α-β phase transformation of quartz

With a simple geometrical model the atomic displacements at the transition from α- to β -quartz and the eigenvector of the soft mode at the Γ -point are related to a single (order-) parameter. The model is refined by taking into account possible distortions of the SiO₄ tetrahedra. These refinements, together with considerations on the temperature dependence of the order parameter, suggest an increase of π-bond order in the Si-O bond with increasing temperature as the driving mechanism for the phase transition. The model also offers a qualitative understanding of the appearance of diffuse X-ray scattering in the Γ-M direction.     

Entmischung im System SnO2?TiO2. Will Kleber zum Gedenken

Exsolution in mixed crystals SnO₂ TiO₂ containing 80 mole% TiO₂ are investigated at temperatures up to 940°C and under pressures of 1,5 and 3 kbars. The existence of an unstable interim phase consisting of lamellae rich in SnO₂ and rich in TiO₂ observed by STUBICAN and SCHULTZ in crystals containing 50 mole% SnO₂ is confirmed. It is shown that the explanation as periodic density fluctuation is wrong. The “side bands” observed in X-ray powder diffraction patterns are due to the different c-lattice-constants. High pressures have a strong retardation effect on exsolution, due to the decrease of the diffusion constant. The presence of water increases the diffusion rate of ions considerably; in powder diffraction the interim phase can only be observed with the aid of asymmetric X-ray reflections. The quantitative interpretation of X-ray diffraction pattern is given in the case of the interim phase. The averaged thicknesses and the Ti-, Sn-concentrations of the lamellae can be given.     

Dispersion of acoustic phonons in layered SrGa2

Acoustic phonon dispersion curves have been determined by inelastic neutron scattering in the intermetallic compound SrGa₂. This compound crystallizes in the AlB₂ type of structure which contains alternating planar Sr and Ga layers normal to the c-axis. The dispersion of the acoustic modes of the three principal directions revealed no strong two dimensional character in terms of sound velocities and elastic constants.     

Synthesis of a tertiary carbinamide via a novel Rh-catalyzed asymmetric hydrogenation

Asymmetric hydrogenation of allylic dimethylcarbinamide 2 with 1 mol % of cationic Rh(I)-Josiphos complex in THF under 500 psi of H2 generated the corresponding tertiary carbinamide 1 in 98.5% assay yield and a 94:6 enantiomeric ratio. Upon crystallization, the product was isolated in 91% isolated yield and 95:5 enantiomeric ratio.     

Preparation and decoherence of superpositions of electromagnetic field states

In a recent experiment the progressive decoherence of a mesoscopic superposition of two coherent field states in a high-Q cavity, known as Schr?dinger cat state, has been measured for the first time [Brune et al., Phys. Rev. Lett. 77, 4887 (1996)]. Here, the full master equation governing the coupled dissipative dynamics of the atom-field system studied in the experiment is formulated and solved numerically for the experimental parameters. The model simulated avoids the approximations underlying an analytically solvable model which is based on a harmonic expansion of the energies of the dressed atomic states and on a treatment of their dynamics within the adiabatic approximation. In particular, the numerical simulations reveal that the coupling of the cavity field mode to its environment causes important decoherence effects already during the initial preparation phase of the Schr?dinger cat state. This phenomenon is investigated in detail with the help of a measure for the purity of states. Moreover, the Hilbert-Schmidt distance of the intended target state, the Schr?dinger cat, to the state that is actually prepared in the experiment is determined. Received 13 September 2000 and Received in final form 22 December 2000