134 research outputs found
Better detection of Multipartite Bound Entanglement with Three-Setting Bell Inequalities
It was shown in Phys. Rev. Lett., 87, 230402 (2001) that N (N >= 4) qubits
described by a certain one parameter family F of bound entangled states violate
Mermin-Klyshko inequality for N >= 8. In this paper we prove that the states
from the family F violate Bell inequalities derived in Phys. Rev. A, 56, R1682
(1997), in which each observer measures three non-commuting sets of orthogonal
projectors, for N >=7. We also derive a simple one parameter family of
entanglement witnesses that detect entanglement for all the states belonging to
F. It is possible that these new entanglement witnesses could be generated by
some Bell inequalities.Comment: Revtex4, 1 figur
Coherent chemical kinetics as quantum walks II: Radical-pair reactions in Arabidopsis thaliana
We apply the quantum-walk approach recently proposed in
arXiv:quant-ph-1506.04213 to a radical-pair reaction where realistic estimates
for the intermediate transition rates are available. The well-known average
hitting time from quantum walks can be adopted as a measure of how quickly the
reaction occurs and we calculate this for varying degrees of dephasing in the
radical pair. The time for the radical pair to react to a product is found to
be independent of the amount of dephasing introduced, even in the limit of no
dephasing where the transient population dynamics exhibit strong coherent
oscillations. This can be seen to arise from the existence of a rate-limiting
step in the reaction and we argue that in such examples, a purely classical
model based on rate equations can be used for estimating the timescale of the
reaction but not necessarily its population dynamics
Entropic Test of Quantum Contextuality
We study the contextuality of a three-level quantum system using classical
conditional entropy of measurement outcomes. First, we analytically construct
the minimal configuration of measurements required to reveal contextuality.
Next, an entropic contextual inequality is formulated, analogous to the
entropic Bell inequalities derived by Braunstein and Caves in [Phys. Rev. Lett.
{\bf 61}, 662 (1988)], that must be satisfied by all non-contextual theories.
We find optimal measurements for violation of this inequality. The approach is
easily extendable to higher dimensional quantum systems and more measurements.
Our theoretical findings can be verified in the laboratory with current
technology.Comment: 4 pages, 4 figure
A note on bound entanglement and local realism
We show using a numerical approach that gives necessary and sufficient
conditions for the existence of local realism, that the bound entangled state
presented in Bennett et. al. Phys. Rev. Lett. 82, 5385 (1999) admits a local
and realistic description. We also find the lowest possible amount of some
appropriate entangled state that must be ad-mixed to the bound entangled state
so that the resulting density operator has no local and realistic description
and as such can be useful in quantum communication and quantum computation.Comment: 5 page
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