12,738 research outputs found
Electrostatics of Gapped and Finite Surface Electrodes
We present approximate methods for calculating the three-dimensional electric
potentials of finite surface electrodes including gaps between electrodes, and
estimate the effects of finite electrode thickness and an underlying dielectric
substrate. As an example we optimize a radio-frequency surface-electrode ring
ion trap, and find that each of these factors reduces the trapping secular
frequencies by less than 5% in realistic situations. This small magnitude
validates the usual assumption of neglecting the influences of gaps between
electrodes and finite electrode extent.Comment: 9 pages, 9 figures (minor changes
Quantum annealing of the Traveling Salesman Problem
We propose a path-integral Monte Carlo quantum annealing scheme for the
symmetric Traveling Salesman Problem, based on a highly constrained Ising-like
representation, and we compare its performance against standard thermal
Simulated Annealing. The Monte Carlo moves implemented are standard, and
consist in restructuring a tour by exchanging two links (2-opt moves). The
quantum annealing scheme, even with a drastically simple form of kinetic
energy, appears definitely superior to the classical one, when tested on a 1002
city instance of the standard TSPLIB.Comment: 5 pages, 2 figure
Investigation of the vibration isolation of commercial jet transport pilots during turbulent air penetration
Electrohydraulic pilot seat isolation system of commercial transport pilots during turbulent air penetratio
Energy Density-Flux Correlations in an Unusual Quantum State and in the Vacuum
In this paper we consider the question of the degree to which negative and
positive energy are intertwined. We examine in more detail a previously studied
quantum state of the massless minimally coupled scalar field, which we call a
``Helfer state''. This is a state in which the energy density can be made
arbitrarily negative over an arbitrarily large region of space, but only at one
instant in time. In the Helfer state, the negative energy density is
accompanied by rapidly time-varying energy fluxes. It is the latter feature
which allows the quantum inequalities, bounds which restrict the magnitude and
duration of negative energy, to hold for this class of states. An observer who
initially passes through the negative energy region will quickly encounter
fluxes of positive energy which subsequently enter the region. We examine in
detail the correlation between the energy density and flux in the Helfer state
in terms of their expectation values. We then study the correlation function
between energy density and flux in the Minkowski vacuum state, for a massless
minimally coupled scalar field in both two and four dimensions. In this latter
analysis we examine correlation functions rather than expectation values.
Remarkably, we see qualitatively similar behavior to that in the Helfer state.
More specifically, an initial negative energy vacuum fluctuation in some region
of space is correlated with a subsequent flux fluctuation of positive energy
into the region. We speculate that the mechanism which ensures that the quantum
inequalities hold in the Helfer state, as well as in other quantum states
associated with negative energy, is, at least in some sense, already
``encoded'' in the fluctuations of the vacuum.Comment: 21 pages, 7 figures; published version with typos corrected and one
added referenc
Quasiparticle decay rate of Josephson charge qubit oscillations
We analyze the decay of Rabi oscillations in a charge qubit consisting of a
Cooper pair box connected to a finite-size superconductor by a Josephson
junction. We concentrate on the contribution of quasiparticles in the
superconductors to the decay rate. Passing of a quasiparticle through the
Josephson junction tunes the qubit away from the charge degeneracy, thus
spoiling the Rabi oscillations. We find the temperature dependence of the
quasiparticle contribution to the decay rate for open and isolated systems. The
former case is realized if a normal-state trap is included in the circuit, or
if just one vortex resides in the qubit; the decay rate has an activational
temperature dependence with the activation energy equal to the superconducting
gap . In a superconducting qubit isolated from the environment, the
activation energy equals if the number of electrons is even, while
for an odd number of electrons the decay rate of an excited qubit state remains
finite in the limit of zero temperature. We estimate the decay rate for
realistic parameters of a qubit.Comment: 8 pages, 3 figures, final version as published in PRB, minor change
Vibrational energy transfer in ultracold molecule - molecule collisions
We present a rigorous study of vibrational relaxation in p-H2 + p-H2
collisions at cold and ultracold temperatures and identify an efficient
mechanism of ro-vibrational energy transfer. If the colliding molecules are in
different rotational and vibrational levels, the internal energy may be
transferred between the molecules through an extremely state-selective process
involving simultaneous conservation of internal energy and total rotational
angular momentum. The same transition in collisions of distinguishable
molecules corresponds to the rotational energy transfer from one vibrational
state of the colliding molecules to another.Comment: 4 pages, 4 figure
The Infrared Extinction Law at Extreme Depth in a Dark Cloud Core
We combined sensitive near-infrared data obtained with ground-based imagers
on the ESO NTT and VLT telescopes with space mid-infrared data acquired with
the IRAC imager on the Spitzer Space Telescope to calculate the extinction law
A_\lambda/A_K as a function of \lambda between 1.25 and 7.76 micron to an
unprecedented depth in Barnard 59, a star forming, dense core located in the
Pipe Nebula. The ratios A_\lambda/A_K were calculated from the slopes of the
distributions of sources in color-color diagrams \lambda-K vs. H-K. The
distributions in the color-color diagrams are fit well with single slopes to
extinction levels of A_K ~ 7 (A_V ~ 59 mag). Consequently, there appears to be
no significant variation of the extinction law with depth through the B59 line
of sight. However, when slopes are translated into the relative extinction
coefficients A_\lambda/A_K, we find an extinction law which departs from the
simple extrapolation of the near-infrared power law extinction curve, and
agrees more closely with a dust extinction model for a cloud with a total to
selective absorption R_V=5.5 and a grain size distribution favoring larger
grains than those in the diffuse ISM. Thus, the difference we observe could be
possibly due to the effect of grain growth in denser regions. Finally, the
slopes in our diagrams are somewhat less steep than those from the study of
Indebetouw et al. (2005) for clouds with lower column densities, and this
indicates that the extinction law between 3 and 8 micron might vary slightly as
a function of environment.Comment: 22 pages manuscript, 4 figures (2 multipart), 1 tabl
Factor ordering in standard quantum cosmology
The Wheeler-DeWitt equation of Friedmann models with a massless quantum field
is formulated with arbitrary factor ordering of the Hamiltonian constraint
operator. A scalar product of wave functions is constructed, giving rise to a
probability interpretation and making comparison with the classical solution
possible. In general the bahaviour of the wave function of the model depends on
a critical energy of the matter field, which, in turn, depends on the chosen
factor ordering. By certain choices of the ordering the critical energy can be
pushed down to zero.Comment: 15 pages, 3 figure
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