Local Invariants and Pairwise Entanglement in Symmetric Multi-qubit System

Pairwise entanglement properties of a symmetric multi-qubit system are analyzed through a complete set of two-qubit local invariants. Collective features of entanglement, such as spin squeezing, are expressed in terms of invariants and a classifcation scheme for pairwise entanglement is proposed. The invariant criteria given here are shown to be related to the recently proposed (Phys. Rev. Lett. 95, 120502 (2005)) generalized spin squeezing inequalities for pairwise entanglement in symmetric multi-qubit states.Comment: 9 pages, 2 figures, REVTEX, Replaced with a published versio

Tree Stands and Their Productivity Dynamics at the Upper Growing Limit in Khibiny on the Background of Modern Climate Changes

Within the ecotone of the upper limit of woody vegetation on the southeastern macroslope of the Khibiny Mountain ridge (Kola Peninsula), the spatial and age structure, as well as features of the phytomass accumulation of spruce–birch stands, were studied. Analysis revealed that there was a manifold increase in the density and productivity of forest stands in the last century, and the upper border of the woodlands and dense forests has moved considerably higher into the mountains. All of this happened against the background of an increase in early summer temperatures and a longer growing season in the area in the 20th century. Our data will help simulate the response of mountain ecosystems in the region to future climate change. © 2019, Pleiades Publishing, Ltd

Wastewater treatment and reuse: an institutional analysis for Hyderabad, India

River basinsWater pollutionSewageEffluentsPollution controlLegislationWaste managementWater qualityGuidelinesWastewater irrigationHealth hazardsRiceGrassesInstitutional reformCase studies

Ferromagnetism in nanoscale BiFeO3

A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40 nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization (~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops, however, exhibit exchange bias as well as vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit characteristic features at the magnetic transition point. These features establish formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO_3.Comment: 13 pages including 4 figures; pdf only; submitted to Appl. Phys. Let

Quantum discord and classical correlation can tighten the uncertainty principle in the presence of quantum memory

Uncertainty relations capture the essence of the inevitable randomness associated with the outcomes of two incompatible quantum measurements. Recently, Berta et al. have shown that the lower bound on the uncertainties of the measurement outcomes depends on the correlations between the observed system and an observer who possesses a quantum memory. If the system is maximally entangled with its memory, the outcomes of two incompatible measurements made on the system can be predicted precisely. Here, we obtain a new uncertainty relation that tightens the lower bound of Berta et al., by incorporating an additional term that depends on the quantum discord and the classical correlations of the joint state of the observed system and the quantum memory. We discuss several examples of states for which our new lower bound is tighter than the bound of Berta et al. On the application side, we discuss the relevance of our new inequality for the security of quantum key distribution and show that it can be used to provide bounds on the distillable common randomness and the entanglement of formation of bipartite quantum states.Comment: v1: Latex, 4 and half pages, one fig; v2: 9 pages including 4-page appendix; v3: accepted into Physical Review A with minor change