203 research outputs found
Complexity measures, emergence, and multiparticle correlations
We study correlation measures for complex systems. First, we investigate some
recently proposed measures based on information geometry. We show that these
measures can increase under local transformations as well as under discarding
particles, thereby questioning their interpretation as a quantifier for
complexity or correlations. We then propose a refined definition of these
measures, investigate its properties and discuss its numerical evaluation. As
an example, we study coupled logistic maps and study the behavior of the
different measures for that case. Finally, we investigate other local effects
during the coarse graining of the complex system.Comment: 13 pages, 5 figures, accepted by Phys. Rev.
Nonlinear entanglement witnesses
Entanglement detection typically relies on linear inequalities for mean
values of certain observables (entanglement witnesses), where violation
indicates entanglement. We provide a general method to improve any of these
inequalities for bipartite systems via nonlinear expressions. The
nonlinearities are of different orders and can be directly measured in
experiments, often without any extra effort.Comment: 4 pages, 1 figure, v3: small changes, final versio
Entanglement criteria for Dicke states
Dicke states are a family of multi-qubit quantum states with interesting
entanglement properties and have been observed in many experiments. We
construct entanglement witnesses for detecting genuine multiparticle
entanglement in the vicinity of these states. We use the approach of PPT
mixtures to derive the conditions analytically. For nearly all cases, our
criteria are stronger than all conditions previously known.Comment: 18 pages, 4 figures; updated to match published versio
- …