2,277 research outputs found
Statistical mechanics of multipartite entanglement
We characterize the multipartite entanglement of a system of n qubits in
terms of the distribution function of the bipartite purity over all balanced
bipartitions. We search for those (maximally multipartite entangled) states
whose purity is minimum for all bipartitions and recast this optimization
problem into a problem of statistical mechanics.Comment: final versio
A Robust Semidefinite Programming Approach to the Separability Problem
We express the optimization of entanglement witnesses for arbitrary bipartite
states in terms of a class of convex optimization problems known as Robust
Semidefinite Programs (RSDP). We propose, using well known properties of RSDP,
several new sufficient tests for the separability of mixed states. Our results
are then generalized to multipartite density operators.Comment: Revised version (minor spell corrections) . 6 pages; submitted to
Physical Review
Decoherence and multipartite entanglement
We study the dynamics of multipartite entanglement under the influence of
decoherence. A suitable generalization of concurrence reveals distinct scaling
of the entanglement decay rate of GHZ and W states, for various environments.Comment: 4 pages, 2 figures, accepted for publication in Phys. Rev. Let
Heuristic for estimation of multiqubit genuine multipartite entanglement
For every N-qubit density matrix written in the computational basis, an
associated "X-density matrix" can be obtained by vanishing all entries out of
the main- and anti-diagonals. It is very simple to compute the genuine
multipartite (GM) concurrence of this associated N-qubit X-state, which,
moreover, lower bounds the GM-concurrence of the original (non-X) state. In
this paper, we rely on these facts to introduce and benchmark a heuristic for
estimating the GM-concurrence of an arbitrary multiqubit mixed state. By
explicitly considering two classes of mixed states, we illustrate that our
estimates are usually very close to the standard lower bound on the
GM-concurrence, being significantly easier to compute. In addition, while
evaluating the performance of our proposed heuristic, we provide the first
characterization of GM-entanglement in the steady states of the driven Dicke
model at zero temperature.Comment: 19 pages, 5 figure
Structural Quantification of Entanglement
We introduce an approach which allows a detailed structural and quantitative
analysis of multipartite entanglement. The sets of states with different
structures are convex and nested. Hence, they can be distinguished from each
other using appropriate measurable witnesses. We derive equations for the
construction of optimal witnesses and discuss general properties arising from
our approach. As an example, we formulate witnesses for a 4-cluster state and
perform a full quantitative analysis of the entanglement structure in the
presence of noise and losses. The strength of the method in multimode
continuous variable systems is also demonstrated by considering a dephased
GHZ-type state.Comment: 12 pages, 1 table and 3 figure
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