70 research outputs found
Entanglement from the vacuum
We explore the entanglement of the vacuum of a relativistic field by letting
a pair of causally disconnected probes interact with the field. We find that,
even when the probes are initially non-entangled, they can wind up to a final
entangled state. This shows that entanglement persists between disconnected
regions in the vacuum. However the probe entanglement, unlike correlations,
vanishes once the regions become sufficiently separated. The relation between
entropy, correlations and entanglement is discussed.Comment: 15 pages, 2 figures, Latex2e, see also quant-ph/0008006. To appear in
a special issue of Foundations of Physics in honor of Jacob Bekenstei
Spatial structures and localization of vacuum entanglement in the linear harmonic chain
We study the structure of vacuum entanglement for two complimentary segments
of a linear harmonic chain, applying the modewise decomposition of entangled
gaussian states discussed in \cite {modewise}. We find that the resulting
entangled mode shape hierarchy shows a distinctive layered structure with well
defined relations between the depth of the modes, their characteristic
wavelength, and their entanglement contribution. We re-derive in the strong
coupling (diverging correlation length) regime, the logarithmic dependence of
entanglement on the segment size predicted by conformal field theory for the
boson universality class, and discuss its relation with the mode structure. We
conjecture that the persistence of vacuum entanglement between arbitrarily
separated finite size regions is connected with the localization of the highest
frequency innermost modes.Comment: 23 pages, 19 figures, RevTex4. High resolution figures available upon
request. New References adde
On the efficiency of nonlocal gates generation
We propose and study a method for using non-maximally entangled states to
implement probabilistically non-local gates. Unlike distillation-based
protocols, this method does not generate a maximally entangled state at
intermediate stages of the process. As a consequences, the method becomes more
efficient at a certain range of parameters. Gates of the form
with , can be implemented with
nearly unit probability and with vanishingly small entanglement, while for the
distillation-based method the gate is produced with a vanishing success
probability. We also derive an upper bound to the optimal success probability
and show that in the small entanglement limit, the bound is tight.Comment: 6 pages, 3 figure
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