Three-photon states in nonlinear crystal superlattices

It has been a longstanding goal in quantum optics to realize controllable sources generating joint multiphoton states, particularly, photon triplet with arbitrary spectral characteristics. We demonstrate that such sources can be realized via cascaded parametric down-conversion (PDC) in superlattice structures of nonlinear and linear segments. We consider scheme that involves two parametric processes: $\omega_{0}\rightarrow\omega_{1}+\omega_{2}$, $\omega_{2}\rightarrow\omega_{1}+\omega_{1}$ under pulsed pump and investigate spontaneous creation of photon triplet as well as generation of high-intensity mode in intracavity three-photon splitting. We show preparation of Greenberger-Horne-Zeilinger polarization entangled states in cascaded type-II and type-I PDC in framework of consideration dual-grid structure that involves two periodically-poled crystals. We demonstrate the method of compensation of the dispersive effects in non-linear segments by appropriately chosen linear dispersive segments of superlattice for preparation heralded joint states of two polarized photons. In the case of intracavity three-photon splitting, we concentrate on investigation of photon-number distributions, third-order photon-number correlation function as well as the Wigner functions. These quantities are observed both for short interaction time intervals and in over transient regime, when dissipative effects are essential.Comment: 15 pages, 6 figure

Perspectives on protected area and wildfire management in the Black Sea region

Protected areas are necessary for the conservation and enhancement of biodiversity. Wildfires are major threats to forests and other natural areas, because they may cause irreversible damages. The aim of this study was to analyze the perspective of experts (N = 284), from six countries of the Black Sea, on the current status and problems of protected areas and wildfires. Understanding their points of view could enhance future management on these issues in the region. Data collection was carried out for 9 months, using a web-based questionnaire. Wildfires were perceived as a serious problem in Turkey, Armenia and Greece but as a substantially less serious problem in Romania, Ukraine and Moldova. In Greece, Armenia, and especially Ukraine, the current designated protected areas are considered sufficient to maintain biodiversity, while in Romania, Turkey, and especially Moldova, more areas should be designated as protected. A major need in all countries (except for Turkey) is the increased use of information and communication technologies for both wildfire suppression and protected area management. Experts were divided on whether wildfire suppression and management of protected areas are interconnected. However, there is growing awareness of the adverse impacts of climate change in protected areas and the frequency of wildfires in the future. The most frequently suggested measures to alleviate these impacts were: changes in forest management and increasing public awareness for wildfire suppression, along with changes in forest management and increased staff training to enhance protected area conservation.EU INTERREG IV "Black Sea Basin Joint Operational Programme 2007-2013" framework, Black Sea Basin Programme, European Union (EU)