255 research outputs found
The field inside a random distribution of parallel dipoles
We determine the probability distribution for the field inside a random
uniform distribution of electric or magnetic dipoles.
For parallel dipoles, simulations and an analytical derivation show that
although the average contribution from any spherical shell around the probe
position vanishes, the Levy stable distribution of the field is symmetric
around a non-vanishing field amplitude.
In addition we show how omission of contributions from a small volume around
the probe leads to a field distribution with a vanishing mean, which, in the
limit of vanishing excluded volume, converges to the shifted distribution.Comment: RevTeX, 4 pages, 3 figures. Submitted to Phys. Rev. Let
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Naval submarine base Kings Bay and Bangor soil evaluations.
This report provides soil evaluation and characterization testing for the submarine bases at Kings Bay, Georgia, and Bangor, Washington, using triaxial testing at high confining pressures with different moisture contents. In general, the samples from the Bangor and Kings Bay sites appeared to be stronger than a previously used reference soil. Assuming the samples of the material were representative of the material found at the sites, they should be adequate for use in the planned construction. Since soils can vary greatly over even a small site, a soil specification for the construction contractor would be needed to insure that soil variations found at the site would meet or exceed the requirements. A suggested specification for the Bangor and Kings Bay soils was presented based on information gathered from references plus data obtained from this study, which could be used as a basis for design by the construction contractor
Scalable ion traps for quantum information processing
We report on the design, fabrication, and preliminary testing of a 150 zone
array built in a `surface-electrode' geometry microfabricated on a single
substrate. We demonstrate transport of atomic ions between legs of a `Y'-type
junction and measure the in-situ heating rates for the ions. The trap design
demonstrates use of a basic component design library that can be quickly
assembled to form structures optimized for a particular experiment
Fluorescence during Doppler cooling of a single trapped atom
We investigate the temporal dynamics of Doppler cooling of an initially hot
single trapped atom in the weak binding regime using a semiclassical approach.
We develop an analytical model for the simplest case of a single vibrational
mode for a harmonic trap, and show how this model allows us to estimate the
initial energy of the trapped particle by observing the fluorescence rate
during the cooling process. The experimental implementation of this temperature
measurement provides a way to measure atom heating rates by observing the
temperature rise in the absence of cooling. This method is technically
relatively simple compared to conventional sideband detection methods, and the
two methods are in reasonable agreement. We also discuss the effects of RF
micromotion, relevant for a trapped atomic ion, and the effect of coupling
between the vibrational modes on the cooling dynamics.Comment: 12 pages, 11 figures, Submitted to Phys. Rev.
A microfabricated surface-electrode ion trap for scalable quantum information processing
We demonstrate confinement of individual atomic ions in a radio-frequency
Paul trap with a novel geometry where the electrodes are located in a single
plane and the ions confined above this plane. This device is realized with a
relatively simple fabrication procedure and has important implications for
quantum state manipulation and quantum information processing using large
numbers of ions. We confine laser-cooled Mg-24 ions approximately 40 micrometer
above planar gold electrodes. We measure the ions' motional frequencies and
compare them to simulations. From measurements of the escape time of ions from
the trap, we also determine a heating rate of approximately five motional
quanta per millisecond for a trap frequency of 5.3 MHz.Comment: 4 pages, 4 figure
Transport of charged particles by adjusting rf voltage amplitudes
We propose a planar architecture for scalable quantum information processing
(QIP) that includes X-junctions through which particles can move without
micromotion. This is achieved by adjusting radio frequency (rf) amplitudes to
move an rf null along the legs of the junction. We provide a proof-of-principle
by transporting dust particles in three dimensions via adjustable rf potentials
in a 3D trap. For the proposed planar architecture, we use regularization
techniques to obtain amplitude settings that guarantee smooth transport through
the X-junction.Comment: 16 pages, 10 figure
A dynamical classification of the range of pair interactions
We formalize a classification of pair interactions based on the convergence
properties of the {\it forces} acting on particles as a function of system
size. We do so by considering the behavior of the probability distribution
function (PDF) P(F) of the force field F in a particle distribution in the
limit that the size of the system is taken to infinity at constant particle
density, i.e., in the "usual" thermodynamic limit. For a pair interaction
potential V(r) with V(r) \rightarrow \infty) \sim 1/r^a defining a {\it
bounded} pair force, we show that P(F) converges continuously to a well-defined
and rapidly decreasing PDF if and only if the {\it pair force} is absolutely
integrable, i.e., for a > d-1, where d is the spatial dimension. We refer to
this case as {\it dynamically short-range}, because the dominant contribution
to the force on a typical particle in this limit arises from particles in a
finite neighborhood around it. For the {\it dynamically long-range} case, i.e.,
a \leq d-1, on the other hand, the dominant contribution to the force comes
from the mean field due to the bulk, which becomes undefined in this limit. We
discuss also how, for a \leq d-1 (and notably, for the case of gravity, a=d-2)
P(F) may, in some cases, be defined in a weaker sense. This involves a
regularization of the force summation which is generalization of the procedure
employed to define gravitational forces in an infinite static homogeneous
universe. We explain that the relevant classification in this context is,
however, that which divides pair forces with a > d-2 (or a < d-2), for which
the PDF of the {\it difference in forces} is defined (or not defined) in the
infinite system limit, without any regularization. In the former case dynamics
can, as for the (marginal) case of gravity, be defined consistently in an
infinite uniform system.Comment: 12 pages, 1 figure; significantly shortened and focussed, additional
references, version to appear in J. Stat. Phy
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