1,976 research outputs found
Limits on the Halo White Dwarf Component of Baryonic Dark Matter from the {\em Hubble Deep Field}
The MACHO collaboration lensing event statistics suggest that a significant
fraction of the dark galactic halo can be comprised of baryonic matter in the
form of white dwarf stars with masses between 0.1 and 1.0 \Msun . Such a halo
white dwarf population, in order to have escaped detection by those who observe
the white dwarf luminosity function of the disk, must have formed from an old
population. The observations indicate that the number of halo white dwarfs per
cubic parsec per unit bolometric magnitude is less than at
\Lsun; the number must rise significantly at lower luminosities to
provide the needed baryonic halo mass. Such white dwarfs may easily escape
detection in most current and earlier surveys. Though it is limited in angular
extent, the {\em Hubble Deep Field} (HDF) probes a sufficient volume of the
galactic halo to provide interesting limits on the number of halo white dwarf
stars, and on the fraction of the halo mass that they can make up. If the HDF
field can be probed for stars down to then the MACHO result suggests
that there could be up to 12 faint halo white dwarfs visible in the HDF.
Finding (or not finding) these stars in turn places interesting constraints on
star formation immediately following the formation of the galaxy.Comment: 10 pages, AASTEX, 1 table, no figures, accepted for publication in
Ap.J. Letter
A Study of the Relative Effectivness of Four Insolubilizing Agents in Starch-Latex and Protein-Latex Coatings
The process of offset lithography requires several unique characteristics in paper. One of these is an ability in the sheet surface to accept water without deteriorating. Offset coatings commonly use starch and protein in their binder systems. These adhesives are inherently water sensitive. The characteristic of water resistance in coated grades can be obtained through the use of crosslinking agents. Among the more commonly used are unreaformaldehyde, melamine-formaldehyde, and glyoxal. A more recent development involves the use of ammonium zirconium carbonate.
Through the years many studies have examined the effects of various insolubilizing agents in starch coatings. Most of these have analyzed only one agent and have all but excluded protein coatings. A need seemed to exist for a comparative analysis of the commonly used insolubilizing agents in both starch and protein coatings. The lack of literature concerning ammonium zirconium carbonate suggested that its analysis should be included.
A series of starch and protein based coatings were prepared using 16 parts adhesive and 100 parts clay. Styrene-butadiene latex was included in both coatings. Urea-formaldehyde, melamine-formaldehyde, and glyoxal were added at levels of 5, 7, 9, 11, and 13 percent based on dry starch or protein. Ammonium zirconium carbonate, due to its purported superior insolubilizing efficiency was added at levels of 1, 3, 5, 7, and 9 percent. A four pound coat weight was applied by a hand-held blade drawdown technique to a 45 pound base sheet.
Testing of water resistance was carried out via an on-press technique. The samples were allowed to cure two months before testing. The samples were allowed to cure two months before testing. Results showed that urea-formaldehyde produced the highest degree of water resistance. Ammonium zirconium carbonate was competitive with UF and MF resins when added at levels greater than 5%, even when those agents were added at higher levels. Glyoxal harmed starch-latex coating water resistance. Analysis of the protein-latex coatings proved inconclusive
Damping of a nanomechanical oscillator strongly coupled to a quantum dot
We present theoretical and experimental results on the mechanical damping of
an atomic force microscope cantilever strongly coupled to a self-assembled InAs
quantum dot. When the cantilever oscillation amplitude is large, its motion
dominates the charge dynamics of the dot which in turn leads to nonlinear,
amplitude-dependent damping of the cantilever. We observe highly asymmetric
lineshapes of Coulomb blockade peaks in the damping that reflect the degeneracy
of energy levels on the dot, in excellent agreement with our strong coupling
theory. Furthermore, we predict that excited state spectroscopy is possible by
studying the damping versus oscillation amplitude, in analogy to varying the
amplitude of an ac gate voltage.Comment: 4+ pages, 4 figure
Sensing distant nuclear spins with a single electron spin
We experimentally demonstrate the use of a single electronic spin to measure
the quantum dynamics of distant individual nuclear spins from within a
surrounding spin bath. Our technique exploits coherent control of the electron
spin, allowing us to isolate and monitor nuclear spins weakly coupled to the
electron spin. Specifically, we detect the evolution of distant individual
carbon-13 nuclear spins coupled to single nitrogen vacancy centers in a diamond
lattice with hyperfine couplings down to a factor of 8 below the electronic
spin bare dephasing rate. Potential applications to nanoscale magnetic
resonance imaging and quantum information processing are discussed.Comment: Corrected typos, updated references. 5 pages, 4 figures, and
supplemental materia
Topological Flat Bands from Dipolar Spin Systems
We propose and analyze a physical system that naturally admits
two-dimensional topological nearly flat bands. Our approach utilizes an array
of three-level dipoles (effective S = 1 spins) driven by inhomogeneous
electromagnetic fields. The dipolar interactions produce arbitrary uniform
background gauge fields for an effective collection of conserved hardcore
bosons, namely, the dressed spin-flips. These gauge fields result in
topological band structures, whose bandgap can be larger than the corresponding
bandwidth. Exact diagonalization of the full interacting Hamiltonian at
half-filling reveals the existence of superfluid, crystalline, and supersolid
phases. An experimental realization using either ultra-cold polar molecules or
spins in the solid state is considered.Comment: 8 pages, 5 figures. V2: Added discussion of optical dressing - final
version as published in Phys. Rev. Let
Quantum Logic between Remote Quantum Registers
We analyze two approaches to quantum state transfer in solid-state spin
systems. First, we consider unpolarized spin-chains and extend previous
analysis to various experimentally relevant imperfections, including quenched
disorder, dynamical decoherence, and uncompensated long range coupling. In
finite-length chains, the interplay between disorder-induced localization and
decoherence yields a natural optimal channel fidelity, which we calculate.
Long-range dipolar couplings induce a finite intrinsic lifetime for the
mediating eigenmode; extensive numerical simulations of dipolar chains of
lengths up to L=12 show remarkably high fidelity despite these decay processes.
We further consider the extension of the protocol to bosonic systems of coupled
oscillators. Second, we introduce a quantum mirror based architecture for
universal quantum computing which exploits all of the spins in the system as
potential qubits. While this dramatically increases the number of qubits
available, the composite operations required to manipulate "dark" spin qubits
significantly raise the error threshold for robust operation. Finally, as an
example, we demonstrate that eigenmode-mediated state transfer can enable
robust long-range logic between spatially separated Nitrogen-Vacancy registers
in diamond; numerical simulations confirm that high fidelity gates are
achievable even in the presence of moderate disorder.Comment: 15 pages, 10 figure
Recommended from our members
Sensing Distant Nuclear Spins with a Single Electron Spin
We experimentally demonstrate the use of a single electronic spin to measure the quantum dynamics of distant individual nuclear spins from within a surrounding spin bath. Our technique exploits coherent control of the electron spin, allowing us to isolate and monitor nuclear spins weakly coupled to the electron spin. Specifically, we detect the evolution of distant individual C13 nuclear spins coupled to single nitrogen vacancy centers in a diamond lattice with hyperfine couplings down to a factor of 8 below the electronic spin bare dephasing rate. Potential applications to nanoscale magnetic resonance imaging and quantum information processing are discussed.Physic
Recommended from our members
Phonon cooling and lasing with nitrogen-vacancy centers in diamond
We investigate the strain-induced coupling between a nitrogen-vacancy impurity and a resonant vibrational mode of a diamond nanoresonator. We show that under near-resonant laser excitation of the electronic states of the impurity, this coupling can modify the state of the resonator and either cool the resonator close to the vibrational ground state or drive it into a large-amplitude coherent state. We derive a semiclassical model to describe both effects and evaluate the stationary state of the resonator mode under various driving conditions. In particular, we find that by exploiting resonant single- and multiphonon transitions between near-degenerate electronic states, the coupling to high-frequency vibrational modes can be significantly enhanced and dominate over the intrinsic mechanical dissipation. Our results show that a single nitrogen-vacancy impurity can provide a versatile tool to manipulate and probe individual phonon modes in nanoscale diamond structures.Physic
Phonon-Induced Spin-Spin Interactions in Diamond Nanostructures: Application to Spin Squeezing
We propose and analyze a novel mechanism for long-range spin-spin interactions in diamond nanostructures. The interactions between electronic spins, associated with nitrogen-vacancy centers in diamond, are mediated by their coupling via strain to the vibrational mode of a diamond mechanical nanoresonator. This coupling results in phonon-mediated effective spin-spin interactions that can be used to generate squeezed states of a spin ensemble. We show that spin dephasing and relaxation can be largely suppressed, allowing for substantial spin squeezing under realistic experimental conditions. Our approach has implications for spin-ensemble magnetometry, as well as phonon-mediated quantum information processing with spin qubits.Physic
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