4,462 research outputs found
Qubitless Quantum Logic
We discuss the implementation of quantum logic in a system of strongly
interacting particles. The implementation is qubitless since ``logical qubits''
don't correspond to any physical two-state subsystems. As an illustration, we
present the results of simulations of the quantum controlled-NOT gate and
Shor's algorithm for a chain of spin-1/2 particles with Heisenberg coupling.
Our proposal extends the current theory of quantum information processing to
include systems with permanent strong coupling between the two-state
subsystems.Comment: 2 figures. Corrected titl
Spin filtering in nanowire directional coupler
The spin transport characteristics of a nanowire directional electronic
coupler have been evaluated theoretically via a transfer matrix approach. The
application of a gate field in the region of mixing allows for control of spin
current through the different leads of the coupler via the Rashba spin-orbit
interaction. The combination of spin-orbit interaction and applied gate
voltages on different legs of the coupler give rise to a controllable
modulation of the spin polarization. Both structural factors and field strength
tuning lead to a rich phenomenology that could be exploited in spintronic
devices.Comment: 9 pages, 4 figure
Electron Scattering in 2D Semiconductors: Contrasting Dirac and Schr\"odinger Behavior
Electronic transport through a material depends on the response to local
perturbations induced by defects or impurities in the material. The scattering
processes can be described in terms of phase shifts and corresponding cross
sections. The multiorbital nature of the spinor states in transition metal
dichalcogenides would naturally suggest the consideration of a massive Dirac
equation to describe the problem, while the parabolic dispersion of its
conduction and valence bands would invite a simpler Schr\"odinger equation
description. Here, we contrast the scattering of massive Dirac particles and
Schr\"odinger electrons, in order to assess different asymptotic regimes (low
and high Fermi energy) for each one of the electronic models and describe their
regime of validity or transition. At low energies, where the dispersion is
approximately parabolic, the scattering processes are dominated by low angular
momentum channels, which results in nearly isotropic scattering amplitudes. On
the other hand, the differential cross section at high Fermi energies exhibits
clear signatures of the linear band dispersion, as the partial phase shifts
approach a non-zero value. We analyze the electronic dynamics by presenting
differential cross sections for both attractive and repulsive scattering
centers. The dissimilar behavior between Dirac and Schr\"odinger carriers
points to the limits and conditions over which different descriptions are
required for the reliable treatment of scattering processes in these materials
Electron Scattering in 2D Semiconductors: Contrasting Dirac and Schr\"odinger Behavior
Electronic transport through a material depends on the response to local
perturbations induced by defects or impurities in the material. The scattering
processes can be described in terms of phase shifts and corresponding cross
sections. The multiorbital nature of the spinor states in transition metal
dichalcogenides would naturally suggest the consideration of a massive Dirac
equation to describe the problem, while the parabolic dispersion of its
conduction and valence bands would invite a simpler Schr\"odinger equation
description. Here, we contrast the scattering of massive Dirac particles and
Schr\"odinger electrons, in order to assess different asymptotic regimes (low
and high Fermi energy) for each one of the electronic models and describe their
regime of validity or transition. At low energies, where the dispersion is
approximately parabolic, the scattering processes are dominated by low angular
momentum channels, which results in nearly isotropic scattering amplitudes. On
the other hand, the differential cross section at high Fermi energies exhibits
clear signatures of the linear band dispersion, as the partial phase shifts
approach a non-zero value. We analyze the electronic dynamics by presenting
differential cross sections for both attractive and repulsive scattering
centers. The dissimilar behavior between Dirac and Schr\"odinger carriers
points to the limits and conditions over which different descriptions are
required for the reliable treatment of scattering processes in these materials
Tuning hole mobility in InP nanowires
Transport properties of holes in InP nanowires were calculated considering
electron-phonon interaction via deformation potentials, the effect of
temperature and strain fields. Using molecular dynamics, we simulate nanowire
structures, LO-phonon energy renormalization and lifetime. The valence band
ground state changes between light- and heavy-hole character, as the strain
fields and the nanowire size are changed. Drastic changes in the mobility arise
with the onset of resonance between the LO-phonons and the separation between
valence subbands.Comment: 4 pages, 4 figure
Aharonov-Bohm interference in quantum ring exciton: effects of built-in electric fields
We report a comprehensive discussion of quantum interference effects due to
the finite structure of excitons in quantum rings and their first experimental
corroboration observed in the optical recombinations. Anomalous features that
appear in the experiments are analyzed according to theoretical models that
describe the modulation of the interference pattern by temperature and built-in
electric fields.Comment: 6 pages, 7 figure
Scleractinian Coral Recruitment to Reefs Physically Damaged by Ship Groundings
The southeast Florida reef system faces a number of stress factors, among which ship groundings are one of the most physically damaging. Portions of the Florida reef tract located near Port Everglades, Broward County, Florida, USA have been damaged by ship groundings. In 2004, physical damage of more than 30,000 m2 was caused by the groundings of two large cargo ships, the MV Eastwind and MV Federal Pescadores. The present study was designed to measure differences of scleractinian coral recruitment patterns (recruit diversity and richness) and rates to these injured sites in comparison to undamaged reef sites. Coral recruitment rates were measured on unglazed ceramic tiles deployed for a period of one year from February 2007 to February 2008 at five different locations: three control sites (including a high coral cover site), and the two ship grounding sites. Morphology and genetic markers including CO1 and cytb were used to identify the coral recruits. A whole genome amplification kit (REPLI-g, Qiagen) was used to obtain sufficient amounts of DNA. Results revealed low recruitment rates (0.5-2.7 recruitsm-2 yr-1) to the studied sites, suggesting a low potential for recovery of the damaged areas
Modifying the lipid content and composition of plant seeds: engineering the production of LC-PUFA
Omega-3 fatty acids are characterized by a double bond at the third carbon atom from the end of the carbon chain. Latterly, long chain polyunsaturated omega-3 fatty acids such as eicosapentaenoic acid (EPA; 20:5Δ5,8,11,14,17) and docosahexanoic acid (DHA; 22:6 Δ4,7,10,13,16,19), which typically only enter the human diet via the consumption of oily fish, have attracted much attention. The health benefits of the omega-3 LC-PUFAs EPA and DHA are now well established. Given the desire for a sustainable supply of omega-LC-PUFA, efforts have focused on enhancing the composition of vegetable oils to include these important fatty acids. Specifically, EPA and DHA have been the focus of much study, with the ultimate goal of producing a terrestrial plant-based source of these so-called fish oils. Over the last decade, many genes encoding the primary LC-PUFA biosynthetic activities have been identified and characterized. This has allowed the reconstitution of the LC-PUFA biosynthetic pathway in oilseed crops, producing transgenic plants engineered to accumulate omega-3 LC-PUFA to levels similar to that found in fish oil. In this review, we will describe the most recent developments in this field and the challenges of overwriting endogenous seed lipid metabolism to maximize the accumulation of these important fatty acids
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