Quantum Entanglement: Separability, Measure, Fidelity of Teleportation and Distillation

Quantum entanglement plays crucial roles in quantum information processing. Quantum entangled states have become the key ingredient in the rapidly expanding field of quantum information science. Although the nonclassical nature of entanglement has been recognized for many years, considerable efforts have been taken to understand and characterize its properties recently. In this review, we introduce some recent results in the theory of quantum entanglement. In particular separability criteria based on the Bloch representation, covariance matrix, normal form and entanglement witness; lower bounds, subadditivity property of concurrence and tangle; fully entangled fraction related to the optimal fidelity of quantum teleportation and entanglement distillation will be discussed in detail.Comment: 63 pages, 4 figure

Two (talking) heads are not better than one

I discuss a scenario in which second expert opinions may not benefit decision making. The introduction of a second expert s the possibility of partisan bickering, which impairs information transmission.second opinion

Entanglement detection and lower bound of convex-roof extension of negativity

We present a set of inequalities based on mean values of quantum mechanical observables nonlinear entanglement witnesses for bipartite quantum systems. These inequalities give rise to sufficient and necessary conditions for separability of all bipartite pure states and even some mixed states. In terms of these mean values of quantum mechanical observables a measurable lower bound of the convex-roof extension of the negativity is derived.Comment: 8 pages, 1 figur