6,855 research outputs found
Convex ordering and quantification of quantumness
The characterization of physical systems requires a comprehensive
understanding of quantum effects. One aspect is a proper quantification of the
strength of such quantum phenomena. Here, a general convex ordering of quantum
states will be introduced which is based on the algebraic definition of
classical states. This definition resolves the ambiguity of the quantumness
quantification using topological distance measures. Classical operations on
quantum states will be considered to further generalize the ordering
prescription. Our technique can be used for a natural and unambiguous
quantification of general quantum properties whose classical reference has a
convex structure. We apply this method to typical scenarios in quantum optics
and quantum information theory to study measures which are based on the
fundamental quantum superposition principle.Comment: 9 pages, 2 figures, revised version; published in special issue "150
years of Margarita and Vladimir Man'ko
Necessary and sufficient conditions for bipartite entanglement
Necessary and sufficient conditions for bipartite entanglement are derived,
which apply to arbitrary Hilbert spaces. Motivated by the concept of witnesses,
optimized entanglement inequalities are formulated solely in terms of arbitrary
Hermitian operators, which makes them useful for applications in experiments.
The needed optimization procedure is based on a separability eigenvalue
problem, whose analytical solutions are derived for a special class of
projection operators. For general Hermitian operators, a numerical
implementation of entanglement tests is proposed. It is also shown how to
identify bound entangled states with positive partial transposition.Comment: 7 pages, 2 figur
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