3,230 research outputs found
Tomographic Characterization of Three-Qubit Pure States with Only Two-Qubit Detectors
A tomographic process for three-qubit pure states using only pairwise
detections is presented.Comment: 3 pages; revtex4; v2: the focus on tomography was emphasized and the
experimental procedure detailed; v3: the text was improved in clarity, some
mistakes were correcte
Scaling laws for the decay of multiqubit entanglement
We investigate the decay of entanglement of generalized N-particle
Greenberger-Horne-Zeilinger (GHZ) states interacting with independent
reservoirs. Scaling laws for the decay of entanglement and for its finite-time
extinction (sudden death) are derived for different types of reservoirs. The
latter is found to increase with the number of particles. However, entanglement
becomes arbitrarily small, and therefore useless as a resource, much before it
completely disappears, around a time which is inversely proportional to the
number of particles. We also show that the decay of multi-particle GHZ states
can generate bound entangled states.Comment: Minor mistakes correcte
Operational interpretations of quantum discord
Quantum discord quantifies non-classical correlations going beyond the
standard classification of quantum states into entangled and unentangled ones.
Although it has received considerable attention, it still lacks any precise
interpretation in terms of some protocol in which quantum features are
relevant. Here we give quantum discord its first operational meaning in terms
of entanglement consumption in an extended quantum state merging protocol. We
further relate the asymmetry of quantum discord with the performance imbalance
in quantum state merging and dense coding.Comment: v4: 5 pages, 1 fig. Refs added, text improved. Main results
unchanged. See arXiv:1008.4135v2 for a related work. v5: close to the
published versio
Multipartite quantum nonlocality under local decoherence
We study the nonlocal properties of two-qubit maximally-entangled and N-qubit
Greenberger-Horne-Zeilinger states under local decoherence. We show that the
(non)resilience of entanglement under local depolarization or dephasing is not
necessarily equivalent to the (non)resilience of Bell-inequality violations.
Apart from entanglement and Bell-inequality violations, we consider also
nonlocality as quantified by the nonlocal content of correlations, and provide
several examples of anomalous behaviors, both in the bipartite and multipartite
cases. In addition, we study the practical implications of these anomalies on
the usefulness of noisy Greenberger-Horne-Zeilinger states as resources for
nonlocality-based physical protocols given by communication complexity
problems. There, we provide examples of quantum gains improving with the number
of particles that coexist with exponentially-decaying entanglement and
non-local contents.Comment: 6 pages, 4 figure
Jardins clonais e jardins de semente para a produção de mudas de cajueiro.
bitstream/CNPAT-2010/7342/1/Dc-051.pd
Jardins clonais e jardins de semente para a produçao de mudas de cajueiro
bitstream/CNPAT/7907/1/doc51.pd
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
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