Time-dependent currents of 1D bosons in an optical lattice

We analyse the time-dependence of currents in a 1D Bose gas in an optical lattice. For a 1D system, the stability of currents induced by accelerating the lattice exhibits a broad crossover as a function of the magnitude of the acceleration, and the strength of the inter-particle interactions. This differs markedly from mean-field results in higher dimensions. Using the infinite Time Evolving Block Decimation algorithm, we characterise this crossover by making quantitative predictions for the time-dependent behaviour of the currents and their decay rate. We also compute the time-dependence of quasi-condensate fractions which can be measured directly in experiments. We compare our results to calculations based on phase-slip methods, finding agreement with the scaling as the particle density increases, but with significant deviations near unit filling.Comment: 19 pages, 10 figure

An image of enduring plurality in economic theory: The root -metaphor theory of Stephen C Pepper

This dissertation establishes an image of enduring plurality in economic theory based on four stable and adequate world hypotheses identified by philosopher of science Stephen C. Pepper. According to Pepper\u27s metaphilosophy---a theory of philosophy---a world hypothesis is a conceptual system founded on a root metaphor. A root metaphor serves as a cognitive focal point or image that guides in the transformation of uncriticized, commonsense, evidence into criticized evidence and thought. A description of a world hypothesis is developed using the root-metaphor method, which derives a unique set of structural categories identified with each root metaphor. In Pepper\u27s system, four sets of structural categories define a metatheoretical taxonomy and reflect discrete manners by which theoreticians transform uncriticized, commonsense evidence into criticized evidence in an attempt to explain the world. The four world hypotheses identified by Pepper in the philosophical literature are formism, mechanism contextualism and organicism. Formism is based on the root metaphor or perceptual experience of similarity, mechanism is based on the image of the machine; contextualism. is founded on the idea of the given event; and organicism is founded on the idea of the historical process. A world hypothesis is found to be adequate if it possesses scope and precision. Each world hypothesis is autonomous and possesses a unique ontological perspective, theory of truth, interpretation of time and causality, and mode of scientific explanation. Based on Pepper\u27s root-metaphor theory, this research shows how four major theoretical perspectives or \u27schools of thought\u27 in economics correspond with the four adequate world hypothesis. Formism is associated with critical realism, which, in turn, is considered by some to be consistent with post-Keynesian economics. Mechanism is associated with neoclassical economics, Contextualism is associated with \u27old\u27 institutional economics. Organicism is associated with Mandan economics. As a result, Pepper\u27s metaphilosophical system provides a possible philosophical and pluralist account for the origins of the four major \u27schools of thought\u27 often cited in the economic literature

Entanglement growth in quench dynamics with variable range interactions

Studying entanglement growth in quantum dynamics provides both insight into the underlying microscopic processes and information about the complexity of the quantum states, which is related to the efficiency of simulations on classical computers. Recently, experiments with trapped ions, polar molecules, and Rydberg excitations have provided new opportunities to observe dynamics with long-range interactions. We explore nonequilibrium coherent dynamics after a quantum quench in such systems, identifying qualitatively different behavior as the exponent of algebraically decaying spin-spin interactions in a transverse Ising chain is varied. Computing the build-up of bipartite entanglement as well as mutual information between distant spins, we identify linear growth of entanglement entropy corresponding to propagation of quasiparticles for shorter range interactions, with the maximum rate of growth occurring when the Hamiltonian parameters match those for the quantum phase transition. Counter-intuitively, the growth of bipartite entanglement for long-range interactions is only logarithmic for most regimes, i.e., substantially slower than for shorter range interactions. Experiments with trapped ions allow for the realization of this system with a tunable interaction range, and we show that the different phenomena are robust for finite system sizes and in the presence of noise. These results can act as a direct guide for the generation of large-scale entanglement in such experiments, towards a regime where the entanglement growth can render existing classical simulations inefficient.Comment: 17 pages, 7 figure

Fault-Tolerant Dissipative Preparation of Atomic Quantum Registers with Fermions

We propose a fault tolerant loading scheme to produce an array of fermions in an optical lattice of the high fidelity required for applications in quantum information processing and the modelling of strongly correlated systems. A cold reservoir of Fermions plays a dual role as a source of atoms to be loaded into the lattice via a Raman process and as a heat bath for sympathetic cooling of lattice atoms. Atoms are initially transferred into an excited motional state in each lattice site, and then decay to the motional ground state, creating particle-hole pairs in the reservoir. Atoms transferred into the ground motional level are no longer coupled back to the reservoir, and doubly occupied sites in the motional ground state are prevented by Pauli blocking. This scheme has strong conceptual connections with optical pumping, and can be extended to load high-fidelity patterns of atoms.Comment: 12 pages, 7 figures, RevTex

Experiences in porting mini-applications to OpenACC and OpenMP on heterogeneous systems

This article studies mini-applications—Minisweep, GenASiS, GPP, and FF—that use computational methods commonly encountered in HPC. We have ported these applications to develop OpenACC and OpenMP versions, and evaluated their performance on Titan (Cray XK7 with K20x GPUs), Cori (Cray XC40 with Intel KNL), Summit (IBM AC922 with Volta GPUs), and Cori-GPU (Cray CS-Storm 500NX with Intel Skylake and Volta GPUs). Our goals are for these new ports to be useful to both application and compiler developers, to document and describe the lessons learned and the methodology to create optimized OpenMP and OpenACC versions, and to provide a description of possible migration paths between the two specifications. Cases where specific directives or code patterns result in improved performance for a given architecture are highlighted. We also include discussions of the functionality and maturity of the latest compilers available on the above platforms with respect to OpenACC or OpenMP implementations

British science fiction and the Cold War, 1945-1969

This thesis examines British Science Fiction between 1945 and 1969 and considers its response to the Cold War. It investigates the generic progression of British SF in the post-war years, assessing the legacy of the pre-war style of scientific romance in selected works from the late 1940s, before exploring its re-engagement with the tradition of disaster fiction in works by John Wyndham and John Christopher in the 1950s. The thesis then moves on to contemplate the writings of the British New Wave and the experimentations with form in the fiction of J.G. Ballard and Brian Aldiss as well as the stories and articles incorporated within New Worlds magazine during Michael Moorcock’s period as editor. Following on from this is a consideration of the emergence of SF film and television in Britain, marking out its convergence with literary works as well as its own distinctive reactions to the changing contexts of the Cold War. This thesis therefore diverges from existing literary histories of post-war British writing, which have largely focused on the numerous crises affecting the literary novel. Such examinations have tended to represent the Cold War as an ancillary theme – despite Britain being the third nation to acquire nuclear weapons – and have generally overlooked Science Fiction as a suitable mode for engaging with the major transformations taking place in post-war British society. Reacting to such assumptions, this thesis argues that British SF was not only a form that responded to the vast technological changes facilitated by the Cold War, but equally, that cultural life during the Cold War presented considerable challenges to Science Fiction itself – with visions of nuclear war and authoritarianism no longer the exclusive property of the speculative imagination but part of everyday life. Additionally, by concentrating on overtly British responses to the Cold War this thesis aims to further illuminate an area of cultural history that has otherwise received limited attention

Novelty Search for Deep Reinforcement Learning Policy Network Weights by Action Sequence Edit Metric Distance

Reinforcement learning (RL) problems often feature deceptive local optima, and learning methods that optimize purely for reward signal often fail to learn strategies for overcoming them. Deep neuroevolution and novelty search have been proposed as effective alternatives to gradient-based methods for learning RL policies directly from pixels. In this paper, we introduce and evaluate the use of novelty search over agent action sequences by string edit metric distance as a means for promoting innovation. We also introduce a method for stagnation detection and population resampling inspired by recent developments in the RL community that uses the same mechanisms as novelty search to promote and develop innovative policies. Our methods extend a state-of-the-art method for deep neuroevolution using a simple-yet-effective genetic algorithm (GA) designed to efficiently learn deep RL policy network weights. Experiments using four games from the Atari 2600 benchmark were conducted. Results provide further evidence that GAs are competitive with gradient-based algorithms for deep RL. Results also demonstrate that novelty search over action sequences is an effective source of selection pressure that can be integrated into existing evolutionary algorithms for deep RL.Comment: Submitted to GECCO 201

Caryosyntrips : a radiodontan from the Cambrian of Spain, USA and Canada

Caryosyntrips appendages have previously been reported from the Burgess Shale (Cambrian, Stage 5), British Columbia, Canada. New specimens of the genus are here reported from the Wheeler Formation (Cambrian, Drumian) and Langston Formation, Spence Shale Member (Cambrian, Stage 5), Utah, USA. The original Burgess Shale specimens are re-examined alongside the new specimens. Caryosyntrips is shown to have paired ventral spines on each podomere. Three species of Caryosyntrips are recognised: C. serratus Daley and Budd, C. camurus nov. sp. and C. durus nov. sp., differentiated by the overall shape of their appendages and arrangement of dorsal and ventral spines. These differences have potential implications for the feeding methods employed by different species of Caryosyntrips. A specimen collected from the upper Valdemiedes Formation of Spain (Cambrian, Stage 4), previously described as the lobopodian Mureropodia apae Gámez Vintaned et al., is reinterpreted as a Caryosyntrips appendage. This identification is supported by the overall shape of the fossil, and the presence, orientation, and height:width ratio, of ventral spines. However the dorsal surface of the appendage is not well preserved, and the appendage and its ventral spines are larger than other known Caryosyntrips. Therefore it is left in open nomenclature as C. cf. camurus. These new finds increase the temporal range of Caryosyntrips (Cambrian Series 2, Stage 4 to Series 3, Drumian) and the geographic range to a new continent, Gondwana