833 research outputs found
Estimating entanglement monotones with a generalization of the Wootters formula
Entanglement monotones, such as the concurrence, are useful tools to
characterize quantum correlations in various physical systems. The computation
of the concurrence involves, however, difficult optimizations and only for the
simplest case of two qubits a closed formula was found by Wootters [Phys. Rev.
Lett. 80, 2245 (1998)]. We show how this approach can be generalized, resulting
in lower bounds on the concurrence for higher dimensional systems as well as
for multipartite systems. We demonstrate that for certain families of states
our results constitute the strongest bipartite entanglement criterion so far;
moreover, they allow to recognize novel families of multiparticle bound
entangled states.Comment: 8 pages, one figure, v2: small change
Measure of multipartite entanglement with computable lower bounds
In this paper, we present a measure of multipartite entanglement
(-nonseparable), -ME concurrence that
unambiguously detects all -nonseparable states in arbitrary dimensions,
where the special case, 2-ME concurrence , is a
measure of genuine multipartite entanglement. The new measure -ME
concurrence satisfies important characteristics of an entanglement measure
including entanglement monotone, vanishing on -separable states, convexity,
subadditivity and strictly greater than zero for all -nonseparable states.
Two powerful lower bounds on this measure are given. These lower bounds are
experimentally implementable without quantum state tomography and are easily
computable as no optimization or eigenvalue evaluation is needed. We illustrate
detailed examples in which the given bounds perform better than other known
detection criteria.Comment: 12 pages, 3 figure
Transport of Entanglement Through a Heisenberg-XY Spin Chain
The entanglement dynamics of spin chains is investigated using Heisenberg-XY
spin Hamiltonian dynamics. The various measures of two-qubit entanglement are
calculated analytically in the time-evolved state starting from initial states
with no entanglement and exactly one pair of maximally-entangled qubits. The
localizable entanglement between a pair of qubits at the end of chain captures
the essential features of entanglement transport across the chain, and it
displays the difference between an initial state with no entanglement and an
initial state with one pair of maximally-entangled qubits.Comment: 5 Pages. 3 Figure
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