64,683 research outputs found
Spin transport in coupled spinor Bose gases
We report direct measurements of spin transport in a trapped, partially
condensed spinor Bose gas. Detailed analyses of spin flux in this
out-of-equilibrium quantum gas are performed by monitoring the flow of atoms in
different hyperfine spin states. The main mechanisms for motion in this system
are exchange scattering and potential energy inhomogeneity, which lead to spin
waves in the normal component and domain formation in the condensate. We find a
large discrepancy in domain formation timescales with those predicted by
potential-driven formation, indicating strong coupling of the condensate to the
normal component spin wave
Noncontact true temperature measurement, 2
A laser pyrometer was developed for acquiring the true temperature of a levitated sample. The reflectivity is measured by first expanding the laser beam to cover the entire cross-sectional surface of the diffuse target. The reflectivity calibration of this system is determined from the surface emissivity of a target with a blackbody cavity. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of the blackbody cavity (emissivity = 1.0) at a known, arbitrary temperature. Since the photosensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. The latest results available from this on-going research indicate that true temperatures thus obtained are in very good quantitative agreement with thermocouple measured temperatures
Spin swap vs. double occupancy in quantum gates
We propose an approach to realize quantum gates with electron spins localized
in a semiconductor that uses double occupancy to advantage. With a fast
(non-adiabatic) time control of the tunnelling, the probability of double
occupancy is first increased and then brought back exactly to zero. The quantum
phase built in this process can be exploited to realize fast quantum
operations. We illustrate the idea focusing on the half-swap operation, which
is the key two-qubit operation needed to build a CNOT gate.Comment: 5 pages, 2 figure
Noncontact temperature pattern measuring device
Laser pyrometer techniques are utilized to accurately image a true temperature distribution on a given target without touching the target and without knowing the localized emissivity of the target. The pyrometer utilizes a very high definition laser beam and photodetector, both having a very narrow focus. The pyrometer is mounted in a mechanism designed to permit the pyrometer to be aimed and focused at precise localized points on the target surface. The pyrometer is swept over the surface area to be imaged, temperature measurements being taken at each point of focus
Spin Hall Effect in Atoms
We propose an optical means to realize a spin hall effect (SHE) in neutral
atomic system by coupling the internal spin states of atoms to radiation. The
interaction between the external optical fields and the atoms creates effective
magnetic fields that act in opposite directions on "electrically" neutral atoms
with opposite spin polarizations. This effect leads to a Landau level structure
for each spin orientation in direct analogy with the familiar SHE in
semiconductors. The conservation and topological properties of the spin
current, and the creation of a pure spin current are discussed.Comment: 4 pages, 2 figure; Final versio
MODELING NONNEGATIVITY VIA TRUNCATED LOGISTIC AND NORMAL DISTRIBUTIONS: AN APPLICATION TO RANCH LAND PRICE ANALYSIS
This study presents an empirical method of modeling the nonnegativity of dependent variables using truncated logistic and normal disturbance distributions. The method is applied in estimating a ranch land hedonic price function. Results show that the degree of truncation is significant.Land Economics/Use,
Traveling wave tube development for a serrodyne re-entrant amplifier
Traveling wave tube development for serrodyne re-entrant amplifie
Six New Galactic Orbits of Globular Clusters in a Milky-Way-Like Galaxy
Absolute proper motions for six new globular clusters have recently been
determined. This motivated us to obtain the Galactic orbits of these six
clusters both in an axisymmetric Galactic potential and in a barred potential,
such as the one of our Galaxy. Orbits are also obtained for a Galactic
potential that includes spiral arms. The orbital characteristics are compared
and discussed for these three cases. Tidal radii and destruction rates are also
computed and discussed.Comment: 29 pages, 11 figures. Accepted for publication in Ap
Adiabatic Elimination in a Lambda System
This paper deals with different ways to extract the effective two-dimensional
lower level dynamics of a lambda system excited by off-resonant laser beams. We
present a commonly used procedure for elimination of the upper level, and we
show that it may lead to ambiguous results. To overcome this problem and better
understand the applicability conditions of this scheme, we review two rigorous
methods which allow us both to derive an unambiguous effective two-level
Hamiltonian of the system and to quantify the accuracy of the approximation
achieved: the first one relies on the exact solution of the Schrodinger
equation, while the second one resorts to the Green's function formalism and
the Feshbach projection operator technique.Comment: 14 pages, 3 figure
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