Role of Quantumness of Correlations in Entanglement Resource Theory

Quantum correlations: entanglement and quantumness of correlations are main resource for quantum information theory. In this chapter it is presented the scenarios which quantumness of correlations plays an interesting role in entanglement distillation protocol. By means of Koashi - Winter relation, it is discussed that quantumness of correlations are related to the irreversibility of the entanglement distillation protocol. The activation protocol is introduced, and it is proved that quantumness of correlations can create distillable entanglement between the system and the measurement apparatus during a local measurement process.Comment: Full chapter contribution of Advanced Technologies of Quantum Key Distribution, ISBN 978-953-51-5289-

Broadcasting Quantum Information using Finite Resources

Measurements can be viewed as interactions between systems and specifically prepared pointers. Ideally, these interactions create accurate copies of the information corresponding to the diagonal of the system's density operator with respect to the measurement basis. However, establishing measurement outcomes as objective facts requires redundancy. We therefore consider the problem of unitarily distributing this information to several quantum memories. We show that the accuracy of this broadcasting process is limited by thermodynamic restrictions on preparing the memories in pure states: ideal broadcasting is impossible using finite resources. For finite-temperature memories we put forward a lower bound on the entropy production of the broadcasting process. This Holevo-Landauer bound demonstrates that the mixedness of the initial memory limits the ability to accurately broadcast information to more than one memory component, thus fundamentally restricting the creation of redundancies while maintaining the integrity of the original information. Finally, we show how the full information can be recovered in the classical limit -- via coarse-graining or asymptotically as the number of subsystems of each memory component increases -- thus elucidating how objective properties can emerge despite inherent imperfections.Comment: 6 pages, 2 figures, 1 caipirinha and 2 capybaras. Comments are welcom

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