A scalable architecture for quantum computation with molecular nanomagnets

A proposal for a magnetic quantum processor that consists of individual molecular spins coupled to superconducting coplanar resonators and transmission lines is carefully examined. We derive a simple magnetic quantum electrodynamics Hamiltonian to describe the underlying physics. It is shown that these hybrid devices can perform arbitrary operations on each spin qubit and induce tunable interactions between any pair of them. The combination of these two operations ensures that the processor can perform universal quantum computations. The feasibility of this proposal is critically discussed using the results of realistic calculations, based on parameters of existing devices and molecular qubits. These results show that the proposal is feasible, provided that molecules with sufficiently long coherence times can be developed and accurately integrated into specific areas of the device. This architecture has an enormous potential for scaling up quantum computation thanks to the microscopic nature of the individual constituents, the molecules, and the possibility of using their internal spin degrees of freedom.Comment: 27 pages, 6 figure

Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions

Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-derived parameters for the primitive model and the Lennard-Jones model with Lorentz-Berthelot mixing rules. The resulting parameters successfully reproduce the lattice properties used to derive them and are free from the influence of any water model. To assess the transferability of the Lennard-Jones parameters to aqueous systems, we used them to estimate hydration free energies and found that the results were in quantitative agreement with experimentally measured values. These lattice-derived parameters are applicable in simulations where coupling of ion parameters to a particular solvent model is undesirable. The simplicity and low computational demands of the calibration procedure make it suitable for parametrization of crystallizable ions in a variety of force fields.Comment: 9 pages, 5 table

Trends in antibacterial resistance among Streptococcus pneumoniae isolated in the USA: update from PROTEKT US Years 1–4

© 2008 Jenkins et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Bosonic Operator Methods for the Quark Model

Quark model matrix elements can be computed using bosonic operators and the holomorphic representation for the harmonic oscillator. The technique is illustrated for normal and exotic baryons for an arbitrary number of colors. The computations are much simpler than those using conventional quark model wavefunctions

Lifting of Ir{100} reconstruction by CO adsorption: An ab initio study

The adsorption of CO on unreconstructed and reconstructed Ir{100} has been studied, using a combination of density functional theory and thermodynamics, to determine the relative stability of the two phases as a function of CO coverage, temperature and pressure. We obtain good agreement with experimentaldata. At zero temperature, the (1X5) reconstruction becomes less stable than the unreconstructed (1X1) surface when the CO coverage exceeds a critical value of 0.09 ML. The interaction between CO molecules is found to be repulsive on the reconstructed surface, but attractive on the unreconstructed, explaining the experimental observation of high CO coverage on growing (1X1) islands. At all temperatures and pressures, we find only two possible stable states: 0.05 ML CO c(2X2) overlayer on the (1X1) substrate, and the clean (1$\times$5) reconstructed surface.Comment: 31 page

Electromagnetic Moments of the Baryon Decuplet

We compute the leading contributions to the magnetic dipole and electric quadrupole moments of the baryon decuplet in chiral perturbation theory. The measured value for the magnetic moment of the $\Omega^-$ is used to determine the local counterterm for the magnetic moments. We compare the chiral perturbation theory predictions for the magnetic moments of the decuplet with those of the baryon octet and find reasonable agreement with the predictions of the large--$N_c$ limit of QCD. The leading contribution to the quadrupole moment of the $\Delta$ and other members of the decuplet comes from one--loop graphs. The pionic contribution is shown to be proportional to $I_z$ (and so will not contribute to the quadrupole moment of $I=0$ nuclei), while the contribution from kaons has both isovector and isoscalar components. The chiral logarithmic enhancement of both pion and kaon loops has a coefficient that vanishes in the $SU(6)$ limit. The third allowed moment, the magnetic octupole, is shown to be dominated by a local counterterm with corrections arising at two loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5

Shocks in supersonic sand

We measure time-averaged velocity, density, and temperature fields for steady granular flow past a wedge and calculate a speed of granular pressure disturbances (sound speed) equal to 10% of the flow speed. The flow is supersonic, forming shocks nearly identical to those in a supersonic gas. Molecular dynamics simulations of Newton's laws and Monte Carlo simulations of the Boltzmann equation yield fields in quantitative agreement with experiment. A numerical solution of Navier-Stokes-like equations agrees with a molecular dynamics simulation for experimental conditions excluding wall friction.Comment: 4 pages, 5 figure

Effective field theory and the quark model

We analyze the connections between the quark model (QM) and the description of hadrons in the low-momentum limit of heavy-baryon effective field theory in QCD. By using a three-flavor-index representation for the effective baryon fields, we show that the ``nonrelativistic'' constituent QM for baryon masses and moments is completely equivalent through O(m_s) to a parametrization of the relativistic field theory in a general spin--flavor basis. The flavor and spin variables can be identified with those of effective valence quarks. Conversely, the spin-flavor description clarifies the structure and dynamical interpretation of the chiral expansion in effective field theory, and provides a direct connection between the field theory and the semirelativistic models for hadrons used in successful dynamical calculations. This allows dynamical information to be incorporated directly into the chiral expansion. We find, for example, that the striking success of the additive QM for baryon magnetic moments is a consequence of the relative smallness of the non-additive spin-dependent corrections.Comment: 25 pages, revtex, no figure

The 2s atomic level in muonic 208-Pb

Relative intensities and energy measurements of 2s level in muonic Pb-20