1,646 research outputs found

    Simple Phase Bias for Superconducting Circuits

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    A phase-bias tool, based on a trapped fluxoid in a ring, is proposed and demonstrated. It can provide arbitrary phase values and is simple to fabricate. The phase bias has been realized in two superconducting quantum interference devices, where the critical current versus magnetic flux is shown to be shifted by a \pi/2 and \pi.Comment: 5 pages, including 4 figures. Submitted to AP

    A scalable architecture for quantum computation with molecular nanomagnets

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    A proposal for a magnetic quantum processor that consists of individual molecular spins coupled to superconducting coplanar resonators and transmission lines is carefully examined. We derive a simple magnetic quantum electrodynamics Hamiltonian to describe the underlying physics. It is shown that these hybrid devices can perform arbitrary operations on each spin qubit and induce tunable interactions between any pair of them. The combination of these two operations ensures that the processor can perform universal quantum computations. The feasibility of this proposal is critically discussed using the results of realistic calculations, based on parameters of existing devices and molecular qubits. These results show that the proposal is feasible, provided that molecules with sufficiently long coherence times can be developed and accurately integrated into specific areas of the device. This architecture has an enormous potential for scaling up quantum computation thanks to the microscopic nature of the individual constituents, the molecules, and the possibility of using their internal spin degrees of freedom.Comment: 27 pages, 6 figure

    Electron beam driven alkali metal atom source for loading a magneto-optical trap in a cryogenic environment

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    We present a versatile and compact electron beam driven source for alkali metal atoms, which can be implemented in cryostats. With a heat load of less than 10mW, the heat dissipation normalized to the atoms loaded into the magneto-optical Trap (MOT), is about a factor 1000 smaller than for a typical alkali metal dispenser. The measured linear scaling of the MOT loading rate with electron current observed in the experiments, indicates that electron stimulated desorption is the corresponding mechanism to release the atoms.Comment: 5 pages, 3 figure

    Ant litter fauna of forest, forest edges and adjacentgrassland in the Atlantic rain forest region of Bahia, Brazil

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    The litter ant fauna was sampled by Winkler sacks and pitfall traps along transects running through Atlantic rain forest into an adjacent grassland. Transects ran 65 m into the forest and 45 m into the field. Ninety-seven species of ants were sampled and scored, 85 were found in the forest, 48 were found in the field and 36 were common to both habitats. There was some evidence that species richness was lowest in the field and high at the deepest point within the forest. The composition of the ant community at the different distances into the forest and field was analysed by a number of hierarchical clustering procedures and also by ordinating the data in three-dimensional space. A two-way table of the ant assemblages derived from the clustering procedure versus the groupings of transect distances obtained by the same procedure indicated that certain ant species had preferences for the field or particular distances into the forest. It is concluded that although the ant fauna of Atlantic rain forest is severely affected by clearing, a forest-like ant fauna is able to persist right up to the interior edge of the forest

    Quantum state transfer in arrays of flux qubits

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    In this work, we describe a possible experimental realization of Bose's idea to use spin chains for short distance quantum communication [S. Bose, {\it Phys. Rev. Lett.} {\bf 91} 207901]. Josephson arrays have been proposed and analyzed as transmission channels for systems of superconducting charge qubits. Here, we consider a chain of persistent current qubits, that is appropriate for state transfer with high fidelity in systems containing flux qubits. We calculate the fidelity of state transfer for this system. In general, the Hamiltonian of this system is not of XXZ-type, and we analyze the magnitude and the effect of the terms that don't conserve the z-component of the total spin.Comment: 10 pages, 8 figure

    Computer Modelling as an Aid to Forest and Woodland Restoration

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    Reclamation of terrestrial ecosystems tends to be focussed on two main land uses, mining and degraded agricultural or forested lands. Modelling has great potential to assist in both situations. The aim of many restoration programs is to restore biodiversity and a self-sustaining, fully functional ecosystem, which is intimately linked with the return of the plants, the vertebrates and, particularly, the invertebrate fauna, whose presence plays a pivotal role in most ecosystem functions and processes. A thorough understanding of these plant-fauna associations is essential if restoration is to succeed. It could also equip us with the knowledge to decide how minimalistic our information needs can be when modelling progress with restoration, for instance: by quantifying certain biophysical parameters; these plus certain vegetation indices; or by both plus a range of faunal attributes. As well as streamlining the restoration monitoring process, this could lead to the enhancement of the conservation value of the restoration, and a clear understanding of the ecological links between flora and fauna would also help develop bioindicators as components of completion criteria schedules. Using Western Australian bauxite mining in the Jarrah (Eucalyptus marginata) forest as a case study, this paper reviews rehabilitation prescriptions and trends in development of plant assemblages, invertebrate colonization and litter decomposition, and applies a systems dynamic modelling approach model to test assumptions regarding the evolution of plant-fauna assemblages in time and assess whether it is feasible to predict temporal changes in the rehabilitation of this ecosystem. Secondly, in relation to efforts to purchase and rehabilitate land to reconnect remnant woodland vegetation close to the south coast of Western Australia, network analysis and multi-level simulations are applied in order to decide the best locations to acquire land and to restore it in order to optimise connectivity

    Diversity and richness of ant species in a lowland wet forest reserve in Sri Lanka

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    Sinharaja Forest Reserve (SFR) represents one of the largest remaining stands of mixed dipterocarp forest in southwestern Sri Lanka. It is characterised by high floral and faunal endemicity and is gazetted as a World Heritage Site. Research was undertaken to study the ground-dwelling ants in the SFR using pitfall traps and leaf litter extraction. The collection was carried out in disturbed and undisturbed primary forest, old selectively-logged forest (30 years old) and periphery forest (agricultural buffer zone) along a small elevation gradient (200 m – 700 m). A total of 173 species and morphospecies in 11 subfamilies and 54 genera were caught. Pheidole and Tetramorium were the most speciose genera, with 19 and 18 species respectively; Cerapachys followed with 12 species. These results demonstrate the high diversity of litter dwelling ant species in the SFR. There were no significant differences in species richness between sites within the forest. Future studies should analyse species assemblages in each forest type in relation to forest structure and environmental parameters to further understand the distribution of ant species across this unique and complex forest
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