Physics – Quantum Physics
Scientific paper
2008-08-19
Phys. Rev. A 78, 062334 (2008).
Physics
Quantum Physics
16 pages, no figures, minor revisions, references added; To appear in Phys. Rev. A
Scientific paper
10.1103/PhysRevA.78.062334
Positivity of the density operator reflects itself in terms of sequences of inequalities on observable moments. Uncertainty relations for non-commuting observables form a subset of these inequalities. In addition, criterion of positivity under partial transposition (PPT) imposes distinct bounds on moments, violations of which signal entanglement. We present bounds on some novel sets of composite moments, consequent to positive partial transposition of the density operator and report their violation by entangled multiqubit states. In particular, we derive separability bounds on a multiqubit moment matrix (based on PPT constraints on bipartite divisions of the density matrix) and show that three qubit pure states with non-zero tangle violate these PPT moment constraints. Further, we recover necessary and sufficient condition of separability in a multiqubit Werner state through PPT bounds on moments.
Rajagopal A. K.
Usha Devi A. R.
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