Width and Magnetic Field Dependence of Transition Temperature in Ultranarrow Superconducting Wires

We calculate the transition temperature in ultranarrow superconducting wires as a function of wire width, resistance and applied magnetic field. We compare the results of first-order perturbation theory and the non-perturbative resummation technique developed by Oreg and Finkel'stein. The latter technique is found to be superior as it is valid even in the strong disorder limit. In both cases the predicted additional suppression of the transition temperature due to the reduced dimensionality is strongly dependent upon the boundary conditions used. When we use the correct (zero-gradient) boundary conditions, we find that theory and experiment are consistent, although more experimental data is required to verify this systematically. We calculate the magnetic field dependence of the transition temperature for different wire widths and resistances in the hope that this will be measured in future experiments. The predicted results have a rich structure - in particular we find a dimensional crossover which can be tuned by varying either the width of the wire or its resistance per square.Comment: 12 pages, 1 table, 7 figures. The changes made to the paper are ones of emphasis. The comparison between theory and experiment has been altered, and detailed comparisons of various approximations have been omitted, although the results are summarised in the paper. Much more emphasis has been placed on the new predictions of the effect of an applied magnetic field on transition temperature in wires (Figs. 5-7

Net Costs of Wildlife Damage on Private Lands

This study models net welfare impacts on producers who receive utility from on-farm wildlife populations that are not costlessly disposable. Wildlife damage levels where net benefits are zero indicate producers' maximum willingness to pay for on-farm wildlife. An empirical model is developed. Results for Ontario producers suggest the net welfare loss from damage is approximately half of the value of the yield loss for those with damage. In aggregate, however, on-farm wildlife generates net benefits to producers that outweigh costs by about 10-to-1. The distribution of net benefits is highly skewed across producers.random effects probit, tolerance thresholds, wildlife benefits, wildlife damage, Resource /Energy Economics and Policy,

Practical repeaters for ultra-long distance quantum communication

The problem of distributing a secret key by quantum channels is one of the preeminent problems in quantum information. To construct such a quantum channel, it is useful to use quantum repeaters, which shorten the distance over which individual photons need to be sent, and thus overcoming the problem of attenuation. Here, we present a method by which a quantum repeater network may be constructed using only existing technology. By taking advantage of the robustness of the processes of double-heralding and brokering, a thorough analysis of the system shows that this gives secret key rates on the order of kilohertz, even over distances of thousands of kilometres