649 research outputs found
Thermal entanglement of spins in a nonuniform magnetic field
We study the effect of inhomogeneities in the magnetic field on the thermal
entanglement of a two spin system. We show that in the ferromagnetic case a
very small inhomogeneity is capable to produce large values of thermal
entanglement. This shows that the absence of entanglement in the ferromagnetic
Heisenberg system is highly unstable against inhomogeneoity of magnetic fields
which is inevitably present in any solid state realization of qubits.Comment: 14 pages, 7 figures, latex, Accepted for publication in Physical
Review
Kader, min Kader?
Denne masteroppgaven i statsvitenskap har vÊrt en bestrebelse i Ä forstÄ hvilke strategier
partiet RĂždt har nyttiggjort seg av i arbeidet med Ă„ Ăžke oppslutningen sin, og om dette kan
skyldes A: Politisk merkevarebygging eller B: Populisme. Innledningsvis blir det
kontekstuelle bakteppet introdusert, som tjener som legitimasjon for hvorfor siktepunktet ble
valgt, og fĂžlgelig hvorfor nettopp dette er interessant.
Videre blir tre separate tidsperioder i partiets historie, introdusert i bolker. Dette for Ă„ gi en
helhetlig og komparativ fremstilling av hvordan partiet har endret karakter gjennom tidene.
Dette blir gjort via empiri som bestÄr av avisartikler, styringsdokumenter og annet som ble
bedĂžmt relevant i denne sammenhengen. Videre diskuteres det i samspill med informantene
rundt vÄre to empiriske forskningsspÞrsmÄl, her flettes egne refleksjoner sammen med
informantenes innspill â som igjen sammenfaller med det teoretiske rammeverket.
Hovedfunnene er at partiet aktivt har gÄtt gjennom en prosess der de har bygget den politiske
merkevaren sin. Sentralt her er sosiologisk samfunnsanalyse, kontroll pÄ narrativet, med
henblikk pÄ en sterk tilstedevÊrelse pÄ sosiale medier, samt bygging av en profil som etter
alle Ăžremerker ser ut til Ă„ utvikle seg til et sosialdemokratisk substitutt. De kommuniserer
populistisk, men som vi gjennomgÄr i selve oppgaven sÄ foreslÄr vi en populisme hjulpet av
post-marxistisk analyse â altsĂ„ ikke slik vi kanskje tradisjonelt forstĂ„r denne mĂ„ten Ă„
kommunisere pÄ. Ingen definitive konklusjoner er trukket i denne oppgaven, men pÄ
bakgrunn av erfaringene som er gjort kan vi konkludere med at undersÞkelsen av vÄre to
empiriske forskningsspÞrsmÄl, har en anselig del av forklaringskraften nÄr en forsÞker Ä svare
pÄ problemstillingen:
«Partiet RÞdt har gÄtt fra Ä vÊre et mikroparti i 2009, til Ä komme over sperregrensen.
Hvordan kan dette oppsvinget i oppslutning forklares som et resultat av a) politisk
merkevarebygging, b) populisme»
Teleportation via thermally entangled state of a two-qubit Heisenberg XX chain
We find that quantum teleportation, using the thermally entangled state of
two-qubit Heisenberg XX chain as a resource, with fidelity better than any
classical communication protocol is possible. However, a thermal state with a
greater amount of thermal entanglement does not necessarily yield better
fidelity. It depends on the amount of mixing between the separable state and
maximally entangled state in the spectra of the two-qubit Heisenberg XX model.Comment: 5 pages, 1 tabl
Quantum Entanglement in Fermionic Lattices
The Fock space of a system of indistinguishable particles is isomorphic (in a
non-unique way) to the state-space of a composite i.e., many-modes, quantum
system. One can then discuss quantum entanglement for fermionic as well as
bosonic systems. We exemplify the use of this notion -central in quantum
information - by studying some e.g., Hubbard,lattice fermionic models relevant
to condensed matter physics.Comment: 4 Pages LaTeX, 1 TeX Figure. Presentation improved, title changed. To
appear in PR
Entanglement in the One-dimensional Kondo Necklace Model
We discuss the thermal and magnetic entanglement in the one-dimensional Kondo
necklace model. Firstly, we show how the entanglement naturally present at zero
temperature is distributed among pairs of spins according to the strength of
the two couplings of the chain, namely, the Kondo exchange interaction and the
hopping energy. The effect of the temperature and the presence of an external
magnetic field is then investigated, being discussed the adjustment of these
variables in order to control the entanglement available in the system. In
particular, it is indicated the existence of a critical magnetic field above
which the entanglement undergoes a sharp variation, leading the ground state to
a completely unentangled phase.Comment: 8 pages, 13 EPS figures. v2: four references adde
NatF Contributes to an Evolutionary Shift in Protein N-Terminal Acetylation and Is Important for Normal Chromosome Segregation
N-terminal acetylation (N-Ac) is a highly abundant eukaryotic protein modification. Proteomics revealed a significant increase in the occurrence of N-Ac from lower to higher eukaryotes, but evidence explaining the underlying molecular mechanism(s) is currently lacking. We first analysed protein N-termini and their acetylation degrees, suggesting that evolution of substrates is not a major cause for the evolutionary shift in N-Ac. Further, we investigated the presence of putative N-terminal acetyltransferases (NATs) in higher eukaryotes. The purified recombinant human and Drosophila homologues of a novel NAT candidate was subjected to in vitro peptide library acetylation assays. This provided evidence for its NAT activity targeting Met-Lys- and other Met-starting protein N-termini, and the enzyme was termed Naa60p and its activity NatF. Its in vivo activity was investigated by ectopically expressing human Naa60p in yeast followed by N-terminal COFRADIC analyses. hNaa60p acetylated distinct Met-starting yeast protein N-termini and increased general acetylation levels, thereby altering yeast in vivo acetylation patterns towards those of higher eukaryotes. Further, its activity in human cells was verified by overexpression and knockdown of hNAA60 followed by N-terminal COFRADIC. NatF's cellular impact was demonstrated in Drosophila cells where NAA60 knockdown induced chromosomal segregation defects. In summary, our study revealed a novel major protein modifier contributing to the evolution of N-Ac, redundancy among NATs, and an essential regulator of normal chromosome segregation. With the characterization of NatF, the co-translational N-Ac machinery appears complete since all the major substrate groups in eukaryotes are accounted for
Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction
We have studied occurrence of quantum phase transition in the one-dimensional
spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi-
partite and multi-partite entanglement point of view. Using exact numerical
solutions, we are able to study such systems up to 24 qubits. The minimum of
the entanglement ratio R \tau 2/\tau 1 < 1, as a novel estimator of
QPT, has been used to detect QPT and our calculations have shown that its
minimum took place at the critical point. We have also shown both the
global-entanglement (GE) and multipartite entanglement (ME) are maximal at the
critical point for the Ising chain with added DM interaction. Using matrix
product state approach, we have calculated the tangle and concurrence of the
model and it is able to capture and confirm our numerical experiment result.
Lack of inversion symmetry in the presence of DM interaction stimulated us to
study entanglement of three qubits in symmetric and antisymmetric way which
brings some surprising results.Comment: 18 pages, 9 figures, submitte
Entanglement and Spontaneous Symmetry Breaking in Quantum Spin Models
It is shown that spontaneous symmetry breaking does not modify the
ground-state entanglement of two spins, as defined by the concurrence, in the
XXZ- and the transverse field Ising-chain. Correlation function inequalities,
valid in any dimensions for these models, are presented outlining the regimes
where entanglement is unaffected by spontaneous symmetry breaking
Natural Thermal and Magnetic Entanglement in 1D Heisenberg Model
We investigate the entanglement between any two spins in a one dimensional
Heisenberg chain as a function of temperature and the external magnetic field.
We find that the entanglement in an antiferromagnetic chain can be increased by
increasing the temperature or the external field. Increasing the field can also
create entanglement between otherwise disentangled spins. This entanglement can
be confirmed by testing Bell's inequalities involving any two spins in the
solid.Comment: 4 pages, 5 figure
Entanglement in quantum computers described by the XXZ model with defects
We investigate how to generate maximally entangled states in systems
characterized by the Hamiltonian of the XXZ model with defects. Some proposed
quantum computers are described by such model. We show how the defects can be
used to obtain EPR states and W states when one or two excitations are
considered.Comment: 4 pages, 1 figur
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