Lieb-Robinson and the butterfly effect

As experiments are increasingly able to probe the quantum dynamics of systems with many degrees of freedom, it is interesting to probe fundamental bounds on the dynamics of quantum information. We elaborate on the relationship between one such bound---the Lieb-Robinson bound---and the butterfly effect in strongly-coupled quantum systems. The butterfly effect implies the ballistic growth of local operators in time, which can be quantified with the "butterfly" velocity $v_B$. Similarly, the Lieb-Robinson velocity places a state independent ballistic upper bound on the size of time evolved operators in non-relativistic lattice models. Here, we argue that $v_B$ is a state-dependent effective Lieb-Robinson velocity. We study the butterfly velocity in a wide variety of quantum field theories using holography and compare with free particle computations to understand the role of strong coupling. We find that, depending on the way length and time scale, $v_B$ acquires a temperature dependence and decreases towards the IR. We also comment on experimental prospects and on the relationship between the butterfly velocity and signaling.Comment: 5+5 pages, 0 figures. v2: updated references and additional clarification

Plant methods:putting the spotlight on technological innovation in the plant sciences.

Plant Methods is a new journal for plant biologists, specialising in the rapid publication of peer-reviewed articles with a focus on technological innovation in the plant sciences. The aim of Plant Methods is to stimulate the development and adoption of new and improved techniques and research tools in plant biology. We hope to promote more consistent standards in the plant sciences, and make readily accessible laboratory and computer-based research tools available to the whole community. This will be achieved by publishing Research articles, Methodology papers and Reviews using the BioMed Central Open Access publishing model. The journal is supported by a prestigious editorial board, whose members all recognise the importance of technological innovation as a driver for basic science

Can the Boat People Assert a Right to Remain in Asylum?

World political reaction to the Southeast Asian refugee crisis has not asserted the refugees\u27 human rights under international law. As a result, most of the refugees lack security from forcible return to the conditions they fled. They would have that security if the world powers act instead to implement non-refoulement, an established moral principle that arguably has attained the status of customary international law

Battle Hymns: The Power and Popularity of Music in the Civil War

Review of: "Battle Hymns: The Power and Popularity of Music in the Civil War," a part of the "Civil War America Series," by Christian McWhirter

Work and Sing: A History of Occupational and Labor Union Songs in the United States

Review of: Work and Sing: A History of Occupational and Labor Union Songs in the United States, by Ronald D. Cohen