16 research outputs found
Covariance matrices and the separability problem
We propose a unifying approach to the separability problem using covariance
matrices of locally measurable observables. From a practical point of view, our
approach leads to strong entanglement criteria that allow to detect the
entanglement of many bound entangled states in higher dimensions and which are
at the same time necessary and sufficient for two qubits. From a fundamental
perspective, our approach leads to insights into the relations between several
known entanglement criteria -- such as the computable cross norm and local
uncertainty criteria -- as well as their limitations.Comment: 4 pages, no figures; v3: final version to appear in PR
Local renormalization method for random systems
In this paper, we introduce a real-space renormalization transformation for
random spin systems on 2D lattices. The general method is formulated for random
systems and results from merging two well known real space renormalization
techniques, namely the strong disorder renormalization technique (SDRT) and the
contractor renormalization (CORE). We analyze the performance of the method on
the 2D random transverse field Ising model (RTFIM).Comment: 12 pages, 13 figures. Submitted to the Special Issue on "Quantum
Information and Many-Body Theory", New Journal of Physics. Editors: M.B.
Plenio, J. Eiser
Separability criteria and entanglement witnesses for symmetric quantum states
We study the separability of symmetric bipartite quantum states and show that
a single correlation measurement is sufficient to detect the entanglement of
any bipartite symmetric state with a non-positive partial transpose. We also
discuss entanglement conditions and entanglement witnesses for states with a
positive partial transpose.Comment: 5 pages, no figures, LaTeX; v2: typos corrected, introduction
extended; v3: small corrections, published version; for the proceedings of
the DPG spring meeting, Hamburg, March 200