111,948 research outputs found
Optimal Alphabetic Ternary Trees
We give a new algorithm to construct optimal alphabetic ternary trees, where
every internal node has at most three children. This algorithm generalizes the
classic Hu-Tucker algorithm, though the overall computational complexity has
yet to be determined
Extended linear regime of cavity-QED enhanced optical circular birefringence induced by a charged quantum dot
Giant optical Faraday rotation (GFR) and giant optical circular birefringence
(GCB) induced by a single quantum-dot spin in an optical microcavity can be
regarded as linear effects in the weak-excitation approximation if the input
field lies in the low-power limit [Hu et al, Phys.Rev. B {\bf 78}, 085307(2008)
and ibid {\bf 80}, 205326(2009)]. In this work, we investigate the transition
from the weak-excitation approximation moving into the saturation regime
comparing a semiclassical approximation with the numerical results from a
quantum optics toolbox [S.M. Tan, J. Opt. B {\bf 1}, 424 (1999)]. We find that
the GFR and GCB around the cavity resonance in the strong coupling regime are
input-field independent at intermediate powers and can be well described by the
semiclassical approximation. Those associated with the dressed state resonances
in the strong coupling regime or merging with the cavity resonance in the
Purcell regime are sensitive to input field at intermediate powers, and cannot
be well described by the semiclassical approximation due to the quantum dot
saturation. As the GFR and GCB around the cavity resonance are relatively
immune to the saturation effects, the rapid read out of single electron spins
can be carried out with coherent state and other statistically fluctuating
light fields. This also shows that high speed quantum entangling gates, robust
against input power variations, can be built exploiting these linear effects.Comment: Section IV has been added to show the linear GFR/GCB is not affected
by high-order dressed state resonances in reflection/transmission spectra. 11
pages, 9 figure
Stray field and superconducting surface spin valve effect in LaCaMnO/YBaCuO bilayers
Electronic transport and magnetization measurements were performed on
LaCaMnO/YBaCuO (LCMO/YBCO) bilayers
below the superconducting transition temperature in order to study the
interaction between magnetism and superconductivity. This study shows that a
substantial number of weakly pinned vortices are induced in the YBCO layer by
the large out-of-plane stray field in the domain walls. Their motion gives rise
to large dissipation peaks at the coercive field. The angular dependent
magnetoresistance (MR) data reveal the interaction between the stripe domain
structure present in the LCMO layer and the vortices and anti-vortices induced
in the YBCO layer by the out-of-plane stray field. In addition, this study
shows that a superconducting surface spin valve effect is present in these
bilayers as a result of the relative orientation between the magnetization at
the LCMO/YBCO interface and the magnetization in the interior of the LCMO layer
that can be tuned by the rotation of a small . This latter finding will
facilitate the development of superconductive magnetoresistive memory devices.
These low-magnetic field MR data, furthermore, suggest that triplet
superconductivity is induced in the LCMO layer, which is consistent with recent
reports of triplet superconductivity in LCMO/YBCO/LCMO trilayers and LCMO/YBCO
bilayers.Comment: 14 pages, 3 figure
Loss-resistant state teleportation and entanglement swapping using a quantum-dot spin in an optical microcavity
We present a scheme for efficient state teleportation and entanglement
swapping using a single quantum-dot spin in an optical microcavity based on
giant circular birefringence. State teleportation or entanglement swapping is
heralded by the sequential detection of two photons, and is finished after the
spin measurement. The spin-cavity unit works as a complete Bell-state analyzer
with a built-in spin memory allowing loss-resistant repeater operation. This
device can work in both the weak coupling and the strong coupling regime, but
high efficiencies and high fidelities are only achievable when the side leakage
and cavity loss is low. We assess the feasibility of this device, and show it
can be implemented with current technology. We also propose a spin manipulation
method using single photons, which could be used to preserve the spin coherence
via spin echo techniques.Comment: The manuscript is extended, including BSA fidelity, efficiency, and a
compatible scheme for spin manipulations and spin echoes to prolong the spin
coherenc
The asymmetric structure of the Galactic halo
Using the stellar photometry catalogue based on the latest data release (DR4)
of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using
star counts is carried out for selected areas of the sky. The sample areas are
selected along a circle at a Galactic latitude of +60, and 10 strips of
high Galactic latitude along different longitudes. Direct statistics of the
data show that the surface densities of from to
are systematically higher than those of from
to , defining a region of overdensity (in the direction of Virgo)
and another one of underdensity (in the direction of Ursa Major) with respect
to an axisymmetric model. It is shown by comparing the results from star counts
in the colour that the density deviations are due to an asymmetry of
the stellar density in the halo. Theoretical models for the surface density
profile are built and star counts are performed using a triaxial halo of which
the parameters are constrained by observational data. Two possible reasons for
the asymmetric structure are discussed.Comment: 17 pages, 7 figures, 5 tables, MNRAS accepte
Some Like It Hot, Some Like It Warm: Phenotyping To Explore Thermotolerance Diversity
Plants have evolved overlapping but distinct cellular responses to different aspects of high temperature stress. These responses include basal thermotolerance, short- and long-term acquired thermotolerance, and thermotolerance to moderately high temperatures. This ‘thermotolerance diversity’ means that multiple phenotypic assays are essential for fully describing the functions of genes involved in heat stress responses. A large number of genes with potential roles in heat stress responses have been identified using genetic screens and genome wide expression studies. We examine the range of phenotypic assays that have been used to characterize thermotolerance phenotypes in both Arabidopsis and crop plants. Three major variables differentiate thermotolerance assays: (1) the heat stress regime used, (2) the developmental stage of the plants being studied, and (3) the actual phenotype which is scored. Consideration of these variables will be essential for deepening our understanding of the molecular genetics of plant thermotolerance
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