Non-Abelian anyons-particles whose exchange noncommutatively transforms a system's quantum state-are widely sought for the exotic fundamental physics they harbour and for quantum computing applications. Numerous blueprints now exist for stabilizing the simplest type of non-Abelian anyon, defects binding Majorana modes, by interfacing widely available materials. Here we introduce a device fabricated from conventional fractional quantum Hall states and s-wave superconductors that supports exotic non-Abelian defects binding parafermionic zero modes, which generalize Majorana bound states. We show that these new modes can be experimentally identified (and distinguished from Majoranas) using Josephson measurements. We also provide a practical recipe for braiding parafermionic zero modes and show that they give rise to non-Abelian statistics. Interestingly, braiding in our setup produces a richer set of topologically protected operations when compared with the Majorana case. As a byproduct, we establish a new, experimentally realistic Majorana platform in weakly spin-orbit-coupled materials such as gallium arsenide.

Non-Abelian anyons promise to reveal spectacular features of quantum mechanics that could ultimately provide the foundation for a decoherence-free quantum computer. A key breakthrough in the pursuit of these exotic particles originated from Read and Green's observation that the Moore-Read quantum Hall state and a (relatively simple) two-dimensional p + ip superconductor both support so-called Ising non-Abelian anyons. Here we establish a similar correspondence between the Z3 Read-Rezayi quantum Hall state and a novel two-dimensional superconductor in which charge-2e Cooper pairs are built from fractionalized quasiparticles. In particular, both phases harbor Fibonacci anyons that-unlike Ising anyons-allow for universal topological quantum computation solely through braiding. Using a variant of Teo and Kane's construction of non-Abelian phases from weakly coupled chains, we provide a blueprint for such a superconductor using Abelian quantum Hall states interlaced with an array of superconducting islands. Fibonacci anyons appear as neutral deconfined particles that lead to a two-fold ground-state degeneracy on a torus. In contrast to a p + ip superconductor, vortices do not yield additional particle types yet depending on non-universal energetics can serve as a trap for Fibonacci anyons. These results imply that one can, in principle, combine well-understood and widely available phases of matter to realize non-Abelian anyons with universal braid statistics. Numerous future directions are discussed, including speculations on alternative realizations with fewer experimental requirements. arXiv:1307.4403v2 [cond-mat.str-el]

SummaryPhotorhabdus and Xenorhabdus bacteria colonize the intestines of the infective soil-dwelling stage of entomophagous nematodes, Heterorhabditis and Steinernema, respectively. These nematodes infect susceptible insect larvae and release the bacteria into the insect blood. The bacteria kill the insect larvae and convert the cadaver into a food source suitable for nematode growth and development. After several rounds of reproduction the nematodes are recolonized by the bacteria before emerging from the insect cadaver into the soil to search for a new host. Photorhabdus and Xenorhabdus bacteria therefore engage in both pathogenic and mutualistic interactions with different invertebrate hosts as obligate components of their life cycle. In this review we aim to describe current knowledge of the molecular mechanisms utilized by Photorhabdus and Xenorhabdus to control their host-dependent interactions. Recent work has established that there is a trade-off between pathogenicity and mutualism in both these species of bacteria suggesting that the transition between these interactions must be under regulatory control. Despite the superficial similarity between the life cycles of these bacteria, it is now apparent that the molecular components of the regulatory networks controlling pathogenicity and mutualism in Photorhabdus and Xenorhabdus are very different.

SummaryBacteria are often found associated with surfaces as sessile bacterial communities called biofilms, and the formation of a biofilm can be split up into different stages each requiring the expression of specific genes. The production of extracellular polysaccharides (EPS) is important for the maturation of biofilms and is controlled by the Rcs two-component pathway in Escherichia coli (and other Gram-negative bacteria). In this study, we show, for the first time, that the RcsC sensor kinase is required for normal biofilm development in E. coli . Moreover, using a combination of DNA macroarray technology and transcriptional fusion analysis, we show that the expression of > > > > 150 genes is controlled by RcsC in E. coli . In silico analyses of the RcsC regulon predicts that 50% of the genes encode proteins that are either localized to the envelope of E. coli or have activities that affect the structure/properties of the bacterial surface, e.g. the production of colanic acid. Moreover, we also show that RcsC is activated during growth on a solid surface. Therefore, we suggest that the RcsC sensor kinase may play an important role in the remodelling of the bacterial surface during growth on a solid surface and biofilm formation.

We express dynamics of domain walls in ferromagnetic nanowires in terms of collective coordinates generalizing Thiele's steady-state results. For weak external perturbations the dynamics is dominated by a few soft modes. The general approach is illustrated on the example of a vortex wall relevant to recent experiments with flat nanowires. A two-mode approximation gives a quantitatively accurate description of both the steady viscous motion of the wall in weak magnetic fields and its oscillatory behavior in moderately high fields above the Walker breakdown.Dynamics of domain walls in nanosized magnetic wires, strips, rings etc. is a subject of practical importance and fundamental interest [1,2]. Nanomagnets typically have two ground states related to each other by the symmetry of time reversal and thus can serve as a memory bit. Switching between these states proceeds via creation, propagation, and annihilation of domain walls with nontrivial internal structure and dynamics. Although domain-wall (DW) motion in macroscopic magnets has been studied for a long time [3], new phenomena arise on the submicron scale where the local (exchange) and long-range (dipolar) forces are of comparable strengths [4]. In this regime, domain walls are textures with a rich internal structure [2,5]. As a result, they have easily excitable internal degrees of freedom. Providing a description of the domain-wall motion in a nanostrip under an applied magnetic field is the main subject of this paper. We specialize to the experimentally relevant case of thin strips with a thickness-to-width ratio t/w ≪ 1.The dynamics of magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation [6] Here m = M/|M|, H eff (r) = −δU/δM(r) is an effective magnetic field derived from the free-energy functional U [M(r)], γ = g|e|/2mc is the gyromagnetic ratio, and α ≪ 1 is Gilbert's damping constant [7]. Equation (1) can be solved exactly only in a few simple cases. Walker [8] considered a one-dimensional domain wall m = m(x, t) in a uniform external magnetic field H||x.At a low applied field the wall exhibits steady motion, m = m(x − vt), with the velocity v ≈ γH∆/α, where ∆ is the wall width. Above a critical field H W = αM/2 magnetization starts to precess, the wall motion acquires an oscillatory component and the average speed of the wall drops sharply. Qualitatively similar behavior has been observed in magnetic nanostrips [1], however, numerical studies demonstrate that Walker's theory fails to provide a quantitative account of both the steady and oscillatory regimes [2].We formulate the dynamics of a magnetic texture in terms of collective coordinates ξ(t) = {ξ 0 , ξ 1 , . . .}, so that m(r, t) = m(r, {ξ(t)}). Although a magnetization field has infinitely many modes, its long-time dynamics-most relevant to the motion of domain walls-is dominated by a small subset of soft modes with long relaxation times. Focusing on soft modes and ignoring hard ones reduces complex field equations of magnetization dynamics to a much simpler problem. In Walke...

Photorhabdus is a member of the family Enterobacteriaceae that lives in a mutualistic association with a Heterorhabditis nematode worm. The nematode worm burrows into insect prey and regurgitates Photorhabdus, which goes on to kill the insect. The nematode feeds off the growing bacteria until the insect tissues are exhausted, whereupon they reassociate and leave the cadaver in search of new prey. This highly efficient partnership has been used for many years as a biological crop protection agent. The dual nature of Photorhabdus as a pathogen and mutualist makes it a superb model for understanding these apparently exclusive activities. Furthermore, recently identified clinical isolates of Photorhabdus are helping us to understand how human pathogens can emerge from the enormous reservoir of invertebrate pathogens in the environment. As Photorhabdus has never been found outside a host animal, its niche represents an entirely biotic landscape. In this review we discuss what molecular adaptations allow this bacterium to complete this fascinating and complex life cycle.

Photorhabdus is a virulent pathogen that kills its insect host by overcoming immune responses. The bacterium also secretes a range of antibiotics to suppress the growth of other invading microorganisms. Here we show that Photorhabdus produces a small-molecule antibiotic (E)-1,3-dihydroxy-2-(isopropyl)-5-(2-phenylethenyl)benzene (ST) that also acts as an inhibitor of phenoloxidase (PO) in the insect host Manduca sexta. The Photorhabdus gene stlA encodes an enzyme that produces cinnamic acid, a key precursor for production of ST, and a mutation in stlA results in loss of ST production and PO inhibitory activity, which are both restored by genetic complementation of the mutant and also by supplying cinnamic acid. ST is produced both in vitro and in vivo in sufficient quantities to account for PO inhibition and is the only detectable solvent-extractable inhibitor. A Photorhabdus stlA ؊ mutant is significantly less virulent, proliferates slower within the host, and provokes the formation of significantly more melanotic nodules than wild-type bacteria. Virulence of the stlA ؊ mutant is also rescued by supplying cinnamic acid. The proximate cause of the virulence effect, however, is the inhibition of PO, because the effect of the stlA ؊ mutation on virulence is abolished in insects in which PO has been knocked down by RNA interference (RNAi). Thus, ST has a dual function both as a PO inhibitor to counter host immune reactions and also as an antibiotic to exclude microbial competitors from the insect cadaver.Photorhabdus luminescens ͉ RNA interference ͉ stilbene ͉ virulence

Commuting between kingdoms: The biosynthesis of the only nonplant stilbene 1 from Photorhabdus bacteria has been solved by identification of all the genes involved in its biosynthesis and by feeding experiments. Stilbene 1 is derived from the condensation of two β‐ketoacyl thioesters and is required for the normal development of Heterorhabditis nematodes, the natural host of Photorhabdus.