Optimal cloning of single photon polarization by coherent feedback of beam splitter losses

Light fields can be amplified by measuring the field amplitude reflected at a beam splitter of reflectivity R and adding a coherent amplitude proportional to the measurement result to the transmitted field. By applying the quantum optical realization of this amplification scheme to single photon inputs, it is possible to clone the polarization states of photons. We show that optimal cloning of single photon polarization is possible when the gain factor of the amplification is equal to the inverse squareroot of 1-R.Comment: 10 pages, including 1 figure, extended from letter to full paper, to be published in New Journal of Physic

Does environmental peacemaking between states work? Insights on cooperative environmental agreements and reconciliation in international rivalries

The literature on environmental peacemaking argues that cooperation in the face of shared environmental challenges can facilitate further cooperation, trust building, and eventually peace between states in conflict. Empirical research on environmental peacemaking, predominantly conducted in the form of single case studies, has so far been inconclusive. This article uses a cross-case, multimethod research design to test the environmental peacemaking proposition. More specifically, it argues that the conclusion of a cooperative environmental agreement can have a positive impact on reconciliation between rival states. Based on a new dataset on international rivalry termination, transboundary protected areas, and international freshwater agreements, this article first conducts a statistical analysis and a qualitative comparative analysis (QCA). The results are then verified and refined by six case studies. Triangulation of findings from the three studies suggests that the conclusion of a cooperative environmental agreement facilitates reconciliation in international rivalries. But this effect is contingent on a number of scope conditions, such as high environmental attention, internal political stability, wider patterns or traditions of environmental cooperation, and already ongoing processes of reconciliation. Still, the findings imply that environmental challenges do not only affect peace and security in a negative way. Addressing them jointly also opens opportunities for peacemaking and peacebuilding between states

Climate war in the Middle East? Drought, the Syrian civil war and the state of climate-conflict research

Purpose of Review This article reviews existing evidence for a climate-conflict link in Syria and examines how the respective debate reproduces three important shortcomings of climate-conflict research. Recent Findings The potential climate-conflict link for Syria can be conceived of as a four-stage process, with various levels of scientific evidence and consensus existing for each stage: (1) climate change inducing the heavy 2006–2009 drought (plausible, but not proven); (2) massive loss of agricultural livelihoods, significantly attributable to the drought (supported by a majority of studies, but contested); (3) massive rural-to-urban migration triggered by livelihood loss in combination with other factors (supported by a majority of studies, but contested); and (4) migration intensifying existing grievances and facilitating the onset of protests and the subsequent civil war (possible, but little knowledge exists). Summary The debate about the Syrian case reproduces three important shortcomings of climate-conflict research: limited dialogue between different methods, an overstatement of differences, and a lack of theoretical engagement. These shortcomings also have adverse impacts in terms of policy advice

Why do conflicts over scarce renewable resources turn violent? A qualitative comparative analysis

This study addresses the question why intergroup conflicts over scarce, renewable resources in peripheral areas of the global South escalate into violence. In order to do so, twenty cases of such conflicts, seven of which turned violent, are analyzed. The method of fuzzy-set qualitative comparative analysis is used in order to bridge the gap between quantitative and qualitative accounts in the field and to detect patterns of conjunctural causation. In theoretical terms, structural conditions (negative othering and high power differences between the conflict parties) and triggering conditions (external resource appropriation and recent political change) of a violent escalation of renewable resource conflicts are distinguished. The empirical results as well as various robustness checks and comparisons with individual cases suggest that the simultaneous presence of negative othering, low power differences and recent political change is a sufficient condition for the violent escalation of conflicts over scarce renewable resources. I conclude that research on socio-environmental conflicts should pay more attention to conjunctural causation, local power differences and qualitatively different forms of conflict and political change

QCA in International Relations: A Review of Strengths, Pitfalls, and Empirical Applications

Qualitative comparative analysis (QCA) is a rapidly emerging method in the field of International Relations (IR). This raises questions about the strengths and pitfalls of QCA in IR research, established good practices, how IR performs against those standards, and which areas require further attention. After a general introduction to the method, we address these questions based on a review of all empirical QCA studies published in IR journals between 1987 and 2020. Results show that QCA has been employed on a wide range of issue areas and is most common in the study of peace and conflict, global environmental politics, foreign policy, and compliance with international regulations. The utilization of QCA offers IR scholars four distinct advantages: the identification of complex causal patterns, the distinction between necessary and sufficient conditions, a middle ground between quantitative and qualitative approaches, and the reinforcement of the strengths of other methods. We find that albeit a few exceptions, IR researchers conduct high-quality QCA research when compared against established standards. However, the field should urgently pay more attention to three issues: the potential of using QCA in combination with other methods, increasing the robustness of QCA results, and strengthening research transparency in QCA applications. Throughout the article, we formulate strategies for improved QCA research in IR

Advancing research on climate change, conflict and migration

Policy makers across the entire globe have repetitively expressed concern about climate change as a trigger of mass migration and increased political instability. Recent research on both climate-conflict and climatemigration linkages has gained significant attention in the scientific and public debate. Both research fields are deeply intertwined and share some common characteristics. They also have been rapidly evolving during the past years with major achievements being made. Perhaps most importantly, an improved understanding of the role of (potential) climate change impacts in migration and conflicts has been achieved, which has been essential for moving beyond environmental determinism toward a more nuanced exploration of the interlinkages between climate, conflict and migration. Yet, significant conversations and uncertainties continue to exist, hence indicating the urgent need for further advances in these fields. Here, we debate cross-cutting and common pitfalls in both research fields and their implications for policy and research. These pitfalls include (i) insufficient attention to context factors and causal chains, (ii) underestimation of complex spatio-temporal patterns, (iii) discrepancies between quantitative and qualitative evidence, (iv) the non-consideration of adaptation strategies, and (v) a narrow spectrum of methods. We illustrate best practices and suggest ways to move the debate forward

On climate, conflict and cumulation: Suggestions for integrative cumulation of knowledge in the research on climate change and violent conflict

Possible links between climate change and intra-state violent conflict have received major scholarly attention in recent years. But with few exceptions there is still a low level of consensus in this research field. The article argues that one reason for this disagreement is a lack of integrative cumulation of knowledge. Such an integrative cumulation is prevented by three obstacles, which have until now hardly been discussed in the literature. The first is the use of inadequate terms, discussed here with a focus on the labels ‘Malthusian’/‘cornucopian’ and the operationalization of key variables. Secondly, the weaknesses of large-N studies in research on climate change and violent conflict are not sufficiently reflected. These include a lack of data on crucial concepts as well as deficits of widely used datasets. Thirdly, literature that deals with a possible link between adverse environmental change and peace (termed here ‘environmental peace perspective’) has neither been systematized nor adequately considered in the debate so far. The article provides examples of these shortcomings and makes suggestions of how to address each of them. It also develops an integrative theoretical framework for the environmental peace perspective which facilitates its consideration in research on climate change and violent conflict

Between redeemer and work of the devil: The transnational Brazilian biofuel discourse

Biofuels have been the subject of heated political discussions, but also of a growing literature on discourses and environmental policies. Previous studies on the issue have, however, neglected the fact that the different discourses about on biofuels are increasingly crossing national boundaries, i.e., that there is a tendency toward transnationalization. In the light of this development the present article analyzes the transnational Brazilian biofuel discourse in the period 2005–2011 with a special emphasis on actors from Brazil, the EU and the USA. By conducting a discourse analysis along the lines of Hajer, five discourse coalitions can be distinguished, each providing a different view on the opportunities, problems and perspectives of biofuel production in Brazil. It is observed that the long-established hegemony of the discourse coalition of biofuel supporters was successfully challenged by a more critical position during the food crisis of 2007/2008. As a result, the discourse coalition of critical supporters—which was committed to sustainable biofuel production via political regulation—prevailed in the transnational Brazilian biofuel discourse and its position was translated into policy measures