5,399 research outputs found
Finite-temperature conductance of strongly interacting quantum wire with a nuclear spin order
We study the temperature dependence of the electrical conductance of a clean
strongly interacting quantum wire in the presence of a helical nuclear spin
order. The nuclear spin helix opens a temperature-dependent partial gap in the
electron spectrum. Using a bosonization framework we describe the gapped
electron modes by sine-Gordon-like kinks. We predict an internal resistivity
caused by an Ohmic-like friction these kinks experience via interacting with
gapless excitations. As a result, the conductance rises from at
temperatures below the critical temperature when nuclear spins are fully
polarized to at higher temperatures when the order is destroyed,
featuring a relatively wide plateau in the intermediate regime. The theoretical
results are compared with the experimental data for GaAs quantum wires obtained
recently by Scheller et al. [Phys. Rev. Lett. 112, 066801 (2014)].Comment: 18 pages, 10 figure
Lifetime of Majorana qubits in Rashba nanowires with non-uniform chemical potential
We study the lifetime of topological qubits based on Majorana bound states
hosted in a one-dimensional Rashba nanowire (NW) with proximity-induced
superconductivity and non-uniform chemical potential needed for manipulation
and read-out. If nearby gates tune the chemical potential locally so that part
of the NW is in the trivial phase, Andreev bound states (ABSs) can emerge which
are localized at the interface between topological and trivial phases with
energies significantly less than the gap. The emergence of such subgap states
strongly decreases the Majorana qubit lifetime at finite temperatures due to
local perturbations that can excite the system into these ABSs. Using Keldysh
formalism, we study such excitations caused by fluctuating charges in
capacitively coupled gates and calculate the corresponding Majorana lifetimes
due to thermal noise, which are shown to be much shorter than those in NWs with
uniform chemical potential.Comment: 9 pages, 8 figure
Noise-resistant device-independent certification of Bell state measurements
Device-independent certification refers to the characterization of an
apparatus without reference to the internal description of other devices. It is
a trustworthy certification method, free of assumption on the underlying
Hilbert space dimension and on calibration methods. We show how it can be used
to quantify the quality of a Bell state measurement, whether deterministic,
partial or probabilistic. Our certification is noise resistant and opens the
way towards the device-independent self-testing of Bell state measurements in
existing experiments.Comment: 5+5 pages, 3+3 figures. See also related work by Marc Olivier Renou
et a
Improving Agriculture Students' Understanding of Global Production Systems through Distance Learning
Globalization is a fundamental force currently shaping agricultural sector throughout the world. To make sound decisions in a globalised economy, agricultural producers and agribusiness managers must have a high level of understanding of the international dimensions of their industry. To address this need, we are developing a course aimed at helping agricultural students better understand the managerial environment faced by producers worldwide. This course will provide students an opportunity to learn about agricultural production, and the context in which it occurs, by analyzing real-world farm case studies in various countries on four continents in both hemispheres of the globe. Eight case studies are being developed to exemplify the production and managerial environment in five different countries (Russia, Australia, Uruguay, Brazil, and the U.S.). Each case study will include a written description of the case, as well as a video tour of the farm and surrounding region and an interview with the farm manager. The case studies will provide the principal building blocks for the comparative farm management systems course to be taught at each of the four cooperating universities. Through the comparative farm management systems course, students will: (1) obtain a better understanding of the production agriculture sectors of the world, (2) discuss regional agricultural economic issues with instructors who are experts from each country, and (3) gain real-world problems solving experience in international settings through case study analysis. The case studies and course curriculum will be made available to other universities through a project web page and distribution of case study CD-ROMs.globalization, international, comparative farm case studies, distance learning, Teaching/Communication/Extension/Profession,
Renewables energies industry in the current investment context
The current shifts in the global energies market lead the expected change in the long term from traditional energies sources, like fossil fuels, to renewable energies sources, e.g. sun, wind, water, energetic wood etc. The major commitments are: sustainability, productivity, smart energy grids and functional energy systems, industrial ecology, green chemistry, bio mimicry, green nanotechnology. The most important investment criterion relies upon efficiency: energy return of invested energy (EROIE), but there are also other relevant issues such as: policies to support RE, e.g. green certificates, legal issues to exploit resources or the capital costs and operational & maintenance costs. Romania’s best RE potential lies in biomass, hydro and wind, but still is a lot to capitalize on geothermal and solar photovoltaic or in conjoint projects between private investors and authorities, especially in waste incineration power plants.Renewable/green energies, CO2 emissions, EROIE, capital costs, O&M costs
Fake Run-Time Selection of Template Arguments in C++
C++ does not support run-time resolution of template type arguments. To
circumvent this restriction, we can instantiate a template for all possible
combinations of type arguments at compile time and then select the proper
instance at run time by evaluation of some provided conditions. However, for
templates with multiple type parameters such a solution may easily result in a
branching code bloat. We present a template metaprogramming algorithm called
for_id that allows the user to select the proper template instance at run time
with theoretical minimum sustained complexity of the branching code.Comment: Objects, Models, Components, Patterns (50th International Conference,
TOOLS 2012
Bipartite nonlocality with a many-body system
We consider a bipartite scenario where two parties hold ensembles of
-spins which can only be measured collectively. We give numerical
arguments supporting the conjecture that in this scenario no Bell inequality
can be violated for arbitrary numbers of spins if only first order moment
observables are available. We then give a recipe to achieve a significant Bell
violation with a split many-body system when this restriction is lifted. This
highlights the strong requirements needed to detect bipartite quantum
correlations in many-body systems device-independently.Comment: 7+5 pages, 4 figure
Short Cycle Covers of Cubic Graphs and Graphs with Minimum Degree Three
The Shortest Cycle Cover Conjecture of Alon and Tarsi asserts that the edges
of every bridgeless graph with edges can be covered by cycles of total
length at most . We show that every cubic bridgeless graph has a
cycle cover of total length at most and every bridgeless
graph with minimum degree three has a cycle cover of total length at most
Degeneracy lifting of Majorana bound states due to electron-phonon interactions
We study theoretically how electron-phonon interaction affects the energies
and level broadening (inverse lifetime) of Majorana bound states (MBSs) in a
clean topological nanowire at low temperatures. At zero temperature, the energy
splitting between the right and left MBSs remains exponentially small with
increasing nanowire length . At finite temperatures, however, the absorption
of thermal phonons leads to the broadening of energy levels of the MBSs that
does not decay with system length, and the coherent absorption/emission of
phonons at opposite ends of the nanowire results in MBSs energy splitting that
decays only as an inverse power-law in . Both effects remain exponential in
temperature. In the case of quantized transverse motion of phonons, the
presence of Van Hove singularities in the phonon density of states causes
additional resonant enhancement of both the energy splitting and the level
broadening of the MBSs. This is the most favorable case to observe the
phonon-induced energy splitting of MBSs as it becomes much larger than the
broadening even if the topological nanowire is much longer than the coherence
length. We also calculate the charge and spin associated with the energy
splitting of the MBSs induced by phonons. We consider both a spinless
low-energy continuum model, which we evaluate analytically, as well as a
spinful lattice model for a Rashba nanowire, which we evaluate numerically
- …