Theoretical study of the polarized electronic absorption spectra of vanadium-doped zircon

The polarized electronic absorption spectra of a blue vanadium-doped zircon single crystal, grown by the flux method, has been studied by quantum chemical (CI) calculations in order to determine the position of the V⁴⁺ dopant in the zircon host structure. Particularly, the excitation energies and polarizations of V⁴⁺ occupying alternate positions, either the zirconium or silicon position or the interstitial site 16g, have been considered. It is concluded that the observed electronic absorption spectra and the color of zirconblue can only be explained if the V⁴⁺ chromophore is placed on the respective interstitial position.     

Trapped-ion quantum simulator: experimental application to nonlinear interferometers

We show how an experimentally realized set of operations on a single trapped ion is sufficient to simulate a wide class of Hamiltonians of a spin-1/2 particle in an external potential. This system is also able to simulate other physical dynamics. As a demonstration, we simulate the action of two nth order nonlinear optical beam splitters comprising an interferometer sensitive to phase shift in one of the interferometer beam paths. The sensitivity in determining these phase shifts increases linearly with n, and the simulation demonstrates that the use of nonlinear beam splitters (n=2,3) enhances this sensitivity compared to the standard quantum limit imposed by a linear beam splitter (n=1).     

Random packings of frictionless particles

We conduct numerical simulations of random packings of frictionless particles at T = 0. The packing fraction where the pressure becomes nonzero is the same as the jamming threshold, where the static shear modulus becomes nonzero. The distribution of threshold packing fractions narrows, and its peak approaches random close packing as the system size increases. For packing fractions within the peak, there is no self-averaging, leading to exponential decay of the interparticle force distribution.     

High Pressure — High Temperature — Synthesis and Properties of Chromium Kyanite, (Al,Cr)2SiO5

At pressures up to 30 kb and temperatures of 1000–1500°C up to 25% of the Al₃₊ in the Al₂SiO₂-polymorph kyanite could be replaced by Cr₃₊ (composition (Al_1.5Cr_0.5)SiO₅). The lattice constants a₀, b₀, c₀ increase by this substitution, whereas the triclinic angles α, β, γ remain virtually unaffected. Cr₃₊ substitutes for Al in the chains of (AlO₃₊)-octahedra parallel to c₀. The reflectance spectrum (240-1000 nm) exhibits the spin-forbidden ruby lines in addition to the spin-allowed transitions in Cr₃₊ in octahedral coordination. The half width (～3.8 kK), position, and shape of the 10 Dq band indicates a symmetry not higher than D_4h for the Cr₃₊-containing octahedra which is in accordance with structure refinement data for pure Kyanite (Burnham 1963).     

Synthesis of 4,5-benzotropones by cyclization of 1,3-bis-silyl enol ethers with 1,2-dialdehydes

The cyclization of 1,3-bis-silyl enol ethers or (2,4-dioxobutylidene)triphenylphosphoranes with phthalic dialdehyde allowed a convenient synthesis of a variety of 4,5-benzotropones. The hydrogenation of benzotropones afforded functionalized benzocycloheptanones which were transformed into tricyclic butenolides.     

Towards a scalable quantum computer/simulator based on trapped ions

We describe the concept and experimental demonstration of the basic building blocks of a scalable quantum computer using trapped-ion qubits. The trap structure is divided into subregions where ion qubits can either be held as memory or subjected to individual rotations and multi-qubit gates in processor zones. Thus, ion qubits can become entangled in one trapping zone, then separated and distributed to separate zones (by switching control-electrode potentials) where subsequent single- and two-ion gates, and/or detection is performed. Recent work using these building blocks includes (1) demonstration of a dense-coding protocol, (2) demonstration of enhanced qubit-detection efficiency using quantum logic, (3) generation of GHZ states and their application to enhanced precision in spectroscopy, and (4) the realization of teleportation with atomic qubits. In the final section an analog quantum computer that could provide a shortcut towards quantum simulations under requirements less demanding than those for a universal quantum computer is also described. PACS 03.67.Lx; 32.80.Qk     

Spectral encoding of the polarization state of light in multiplexed polarization-sensitive lasing structures

We report the experimental demonstration of spectral encoding of the polarization state of light by use of multiplexed distributed-feedback lasers in a dye-doped organic thin film by exploiting the pump polarization selectivity of the superimposed resonators. Measurement of the Stokes parameters of the pump light without a priori knowledge of the lasing properties of the structure is discussed.     

Experimental demonstration of a technique to generate arbitrary quantum superposition states of a harmonically bound spin-1/2 particle

Using a single, harmonically trapped 9Be(+) ion, we experimentally demonstrate a technique for generation of arbitrary states of a two-level particle confined by a harmonic potential. Rather than engineering a single Hamiltonian that evolves the system to a desired final state, we implement a technique that applies a sequence of simple operations to synthesize the state.