347 research outputs found
Witnessed entanglement and the geometric measure of quantum discord
We establish relations between geometric quantum discord and entanglement
quantifiers obtained by means of optimal witness operators. In particular, we
prove a relation between negativity and geometric discord in the
Hilbert-Schmidt norm, which is slightly different from a previous conjectured
one [Phys. Rev. A 84, 052110 (2011)].We also show that, redefining the
geometric discord with the trace norm, better bounds can be obtained. We
illustrate our results numerically.Comment: 8 pages + 3 figures. Revised version with erratum for PRA 86, 024302
(2012). Simplified proof that discord is bounded by entanglement in any nor
Viable entanglement detection of unknown mixed states in low dimensions
We explore procedures to detect entanglement of unknown mixed states, which
can be experimentally viable. The heart of the method is a hierarchy of simple
feasibility problems, which provides sufficient conditions to entanglement. Our
numerical investigations indicate that the entanglement is detected with a cost
which is much lower than full state tomography. The procedure is applicable to
both free and bound entanglement, and involves only single copy measurements.Comment: 8 pages, 9 figures, 4 table
Witnessed Entanglement
We present a new measure of entanglement for mixed states. It can be
approximately computable for every state and can be used to quantify all
different types of multipartite entanglement. We show that it satisfies the
usual properties of a good entanglement quantifier and derive relations between
it and other entanglement measures.Comment: Revised version. 7 pages and one figur
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