8,804 research outputs found
Magic composite pulses
I describe composite pulses during which the average dipolar interactions
within a spin ensemble are controlled while realizing a global rotation. The
construction method used is based on the average Hamiltonian theory and rely on
the geometrical properties of the spin-spin dipolar interaction only. I present
several such composite pulses robust against standard experimental defects in
NRM: static or radio-frequency field miscalibration, fields inhomogeneities.
Numerical simulations show that the magic sandwich pulse sequence, a pulse
sequence that reverse the average dipolar field while applied, is plagued by
defects originating from its short initial and final \pi/2 radio-frequency
pulses. Using the magic composite pulses instead of \pi/2 pulses improves the
magic sandwich effect. A numerical test using a classical description of NMR
allows to check the validity of the magic composite pulses and estimate their
efficiency.Comment: 22 pages, 6 figure
ELSA: An Integrated, Semi-Automated Nebular Abundance Package
We present ELSA, a new modular software package, written in C, to analyze and
manage spectroscopic data from emission-line objects. In addition to
calculating plasma diagnostics and abundances from nebular emission lines, the
software provides a number of convenient features including the ability to
ingest logs produced by IRAF's splot task, to semi-automatically merge spectra
in different wavelength ranges, and to automatically generate various data
tables in machine-readable or LaTeX format. ELSA features a highly
sophisticated interstellar reddening correction scheme that takes into account
temperature and density effects as well as He II contamination of the hydrogen
Balmer lines. Abundance calculations are performed using a 5-level atom
approximation with recent atomic data, based on R. Henry's ABUN program.
Improvements planned in the near future include use of a three-region
ionization model, similar to IRAF's nebular package, error propagation, and the
addition of ultraviolet and infrared line analysis capability. Detailed
documentation for all aspects of ELSA are available at
http://www.williams.edu/Astronomy/research/PN .Comment: 2 pages, contributed paper, IAU Symp. 234, Planetary Nebulae in Our
Galaxy and Beyon
Techniques for the realization of ultrareliable spaceborne computers Interim scientific report
Error-free ultrareliable spaceborne computer
Design of a fault tolerant airborne digital computer. Volume 1: Architecture
This volume is concerned with the architecture of a fault tolerant digital computer for an advanced commercial aircraft. All of the computations of the aircraft, including those presently carried out by analogue techniques, are to be carried out in this digital computer. Among the important qualities of the computer are the following: (1) The capacity is to be matched to the aircraft environment. (2) The reliability is to be selectively matched to the criticality and deadline requirements of each of the computations. (3) The system is to be readily expandable. contractible, and (4) The design is to appropriate to post 1975 technology. Three candidate architectures are discussed and assessed in terms of the above qualities. Of the three candidates, a newly conceived architecture, Software Implemented Fault Tolerance (SIFT), provides the best match to the above qualities. In addition SIFT is particularly simple and believable. The other candidates, Bus Checker System (BUCS), also newly conceived in this project, and the Hopkins multiprocessor are potentially more efficient than SIFT in the use of redundancy, but otherwise are not as attractive
Geometric Aspects of Composite Pulses
Unitary operations acting on a quantum system must be robust against
systematic errors in control parameters for reliable quantum computing.
Composite pulse technique in nuclear magnetic resonance (NMR) realises such a
robust operation by employing a sequence of possibly poor quality pulses. In
this article, we demonstrate that two kinds of composite pulses, one
compensates for a pulse length error in a one-qubit system and the other
compensates for a J-coupling error in a twoqubit system, have vanishing
dynamical phase and thereby can be seen as geometric quantum gates, which
implement unitary gates by the holonomy associated with dynamics of cyclic
vectors defined in the text.Comment: 20 pages, 4 figures. Accepted for publication in Philosophical
Transactions of the Royal Society
A First Principles Theory of Nuclear Magnetic Resonance J-Coupling in solid-state systems
A method to calculate NMR J-coupling constants from first principles in
extended systems is presented. It is based on density functional theory and is
formulated within a planewave-pseudopotential framework. The all-electron
properties are recovered using the projector augmented wave approach. The
method is validated by comparison with existing quantum chemical calculations
of solution-state systems and with experimental data. The approach has been
applied to verify measured J-coupling in a silicophosphate structure,
Si5O(PO4)6Comment: 9 page
Phase space spinor amplitudes for spin 1/2 systems
The concept of phase space amplitudes for systems with continuous degrees of
freedom is generalized to finite-dimensional spin systems. Complex amplitudes
are obtained on both a sphere and a finite lattice, in each case enabling a
more fundamental description of pure spin states than that previously given by
Wigner functions. In each case the Wigner function can be expressed as the star
product of the amplitude and its conjugate, so providing a generalized Born
interpretation of amplitudes that emphasizes their more fundamental status. The
ordinary product of the amplitude and its conjugate produces a (generalized)
spin Husimi function. The case of spin-\half is treated in detail, and it is
shown that phase space amplitudes on the sphere transform correctly as spinors
under under rotations, despite their expression in terms of spherical
harmonics. Spin amplitudes on a lattice are also found to transform as spinors.
Applications are given to the phase space description of state superposition,
and to the evolution in phase space of the state of a spin-\half magnetic
dipole in a time-dependent magnetic field.Comment: 19 pages, added new results, fixed typo
Tungsten resonance integrals and Doppler coefficients Third quarterly report, Jan. - Mar. 1966
Reactivities, Doppler coefficients, and resonance integrals for tungsten isotope
Quantum information processing using strongly-dipolar coupled nuclear spins
Dipolar coupled homonuclear spins present challenging, yet useful systems for
quantum information processing. In such systems, eigenbasis of the system
Hamiltonian is the appropriate computational basis and coherent control can be
achieved by specially designed strongly modulating pulses. In this letter we
describe the first experimental implementation of the quantum algorithm for
numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR
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