1,041 research outputs found
Detection of Multiparticle Entanglement: Quantifying the Search for Symmetric Extensions
We provide quantitative bounds on the characterisation of multiparticle
separable states by states that have locally symmetric extensions. The bounds
are derived from two-particle bounds and relate to recent studies on quantum
versions of de Finetti's theorem. We discuss algorithmic applications of our
results, in particular a quasipolynomial-time algorithm to decide whether a
multiparticle quantum state is separable or entangled (for constant number of
particles and constant error in the LOCC or Frobenius norm). Our results
provide a theoretical justification for the use of the Search for Symmetric
Extensions as a practical test for multiparticle entanglement.Comment: 5 pages, 1 figur
Macroscopic Entanglement and Phase Transitions
This paper summarises the results of our research on macroscopic entanglement
in spin systems and free Bosonic gases. We explain how entanglement can be
observed using entanglement witnesses which are themselves constructed within
the framework of thermodynamics and thus macroscopic observables. These
thermodynamical entanglement witnesses result in bounds on macroscopic
parameters of the system, such as the temperature, the energy or the
susceptibility, below which entanglement must be present. The derived bounds
indicate a relationship between the occurrence of entanglement and the
establishment of order, possibly resulting in phase transition phenomena. We
give a short overview over the concepts developed in condensed matter physics
to capture the characteristics of phase transitions in particular in terms of
order and correlation functions. Finally we want to ask and speculate whether
entanglement could be a generalised order concept by itself, relevant in
(quantum induced) phase transitions such as BEC, and that taking this view may
help us to understand the underlying process of high-T superconductivity.Comment: 9 pages, 7 figures (color), Submitted to special OSID issue,
Proceedings of the 38th Symposium on Mathematical Physics - Quantum
Entanglement & Geometry, Torun (Poland), June 200
Entangled inputs cannot make imperfect quantum channels perfect
Entangled inputs can enhance the capacity of quantum channels, this being one
of the consequences of the celebrated result showing the non-additivity of
several quantities relevant for quantum information science. In this work, we
answer the converse question (whether entangled inputs can ever render noisy
quantum channels have maximum capacity) to the negative: No sophisticated
entangled input of any quantum channel can ever enhance the capacity to the
maximum possible value; a result that holds true for all channels both for the
classical as well as the quantum capacity. This result can hence be seen as a
bound as to how "non-additive quantum information can be". As a main result, we
find first practical and remarkably simple computable single-shot bounds to
capacities, related to entanglement measures. As examples, we discuss the qubit
amplitude damping and identify the first meaningful bound for its classical
capacity.Comment: 5 pages, 2 figures, an error in the argument on the quantum capacity
corrected, version to be published in the Physical Review Letter
Schmidt balls around the identity
Robustness measures as introduced by Vidal and Tarrach [PRA, 59, 141-155]
quantify the extent to which entangled states remain entangled under mixing.
Analogously, we introduce here the Schmidt robustness and the random Schmidt
robustness. The latter notion is closely related to the construction of Schmidt
balls around the identity. We analyse the situation for pure states and provide
non-trivial upper and lower bounds. Upper bounds to the random Schmidt-2
robustness allow us to construct a particularly simple distillability
criterion. We present two conjectures, the first one is related to the radius
of inner balls around the identity in the convex set of Schmidt number
n-states. We also conjecture a class of optimal Schmidt witnesses for pure
states.Comment: 7 pages, 1 figur
Are all maximally entangled states pure?
We study if all maximally entangled states are pure through several
entanglement monotones. In the bipartite case, we find that the same conditions
which lead to the uniqueness of the entropy of entanglement as a measure of
entanglement, exclude the existence of maximally mixed entangled states. In the
multipartite scenario, our conclusions allow us to generalize the idea of
monogamy of entanglement: we establish the \textit{polygamy of entanglement},
expressing that if a general state is maximally entangled with respect to some
kind of multipartite entanglement, then it is necessarily factorized of any
other system.Comment: 5 pages, 1 figure. Proof of theorem 3 corrected e new results
concerning the asymptotic regime include
Remarks on the equivalence of full additivity and monotonicity for the entanglement cost
We analyse the relationship between the full additivity of the entanglement cost and its full monotonicity under local operations and classical communication. We show that the two properties are equivalent for the entanglement cost. The proof works for the regularization of any convex, subadditive, and asymptotically continuous entanglement monotone, and hence also applies to the asymptotic relative entropy of entanglement
Mosaico de imagens de satélite do Pantanal no ano 2000.
O Pantanal devido a sua extensão e dificuldade de acesso representa um desafio para o desenvolvimento de atividades de produção e conservação da natureza. Nesse sentido as tecnologias de Sensoriamento Remoto podem contribuir muito para o conhecimento e manejo desse ecossistema. O presente trabalho apresenta o mosaico de imagens Landsat 7 ETM do ano 2000 do Pantanal, onde ao contrário dos demais produtos dessa natureza, apresenta uma maior precisão de posicionamento em função de um extenso trabalho de campo realizado para o georreferenciamento das imagens. Esse trabalho é o resultado da parceria entre a Embrapa Pantanal e a WWF Brasil e está disponível também na homepage da Embrapa Pantanal. Esperamos com essa iniciativa estar cumprindo com nosso objetivo de levar à comunidade informações sobre o Pantanal.bitstream/item/81191/1/DOC43.pd
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