A Proposal to Measure the Quasiparticle Poisoning Time of Majorana Bound States

We propose a method of measuring the fermion parity lifetime of Majorana fermion modes due to quasiparticle poisoning. We model quasiparticle poisoning by coupling the Majorana modes to electron reservoirs, explicitly breaking parity conservation in the system. This poisoning broadens and shortens the resonance peak associated with Majorana modes. In a two lead geometry, the poisoning decreases the correlation in current noise between the two leads from the maximal value characteristic of crossed Andreev reflection. The latter measurement allows for calculation of the poisoning rate even if temperature is much higher than the resonance width.Comment: 5 pages, 5 figure

Additional development of large diameter carbon monofilament

The chemical vapor process for preparing a large diameter carbon-base monofilament from a BCl3, Ch4 and H2 gas mixture with a carbon substrate fiber was studied. The effect of reactor geometry, total gas flows and deposition temperature on the tensile strength of the monofilament were investigated. It was noted that consistent results could only be obtained when the carbon substrate fiber was cleaned. The strength of the monofilament was found to depend on the highest temperature and the temperature profile of the monofilament in the reactor. The strength of monofilament produced in the dc and RF reactors were found to be similar and similar alloy compositions in the monofilament were attained when the same gas ratios were used. The tensile strength of the monofilament at 500 C was found to be 60 to 70% of the room temperature tensile strength. No degradation was noted after exposure to molten aluminum

The magneto-optical Faraday effect in spin liquid candidates

We propose an experiment to use the magneto-optical Faraday effect to probe the dynamic Hall conductivity of spin liquid candidates. Theory predicts that an external magnetic field will generate an internal gauge field. If the source of conductivity is in spinons with a Fermi surface, a finite Faraday rotation angle is expected. We predict the angle to scale as the square of the frequency rather than display the standard cyclotron resonance pattern. Furthermore, the Faraday effect should be able to distinguish the ground state of the spin liquid, as we predict no rotation for massless Dirac spinons. We give a semiquantitative estimate for the magnitude of the effect and find that it should be experimentally feasible to detect in both $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ and, if the spinons form a Fermi surface, Herbertsmithite. We also comment on the magneto-optical Kerr effect and show that the imaginary part of the Kerr angle may be measurable.Comment: 5 pages, 1 figur

A Portable, Low-Cost Wheelchair Ergometer Design Based on a Mathematical Model of Pediatric Wheelchair Dynamics

Evaluation and training of wheelchair propulsion improves efficiency and prevents orthopaedic injury in pediatric manual wheelchair users. Ergometers allow static propulsion and emulate typical conditions. Currently available ergometers have deficiencies that limit their use in motion analysis. A new ergometer is developed and evaluated based on a model of wheelchair inertial dynamics that eliminates these deficiencies. This makes integrated motion analysis of wheelchair propulsion in current community, home, and international outreach efforts possible

Realizable Hamiltonians for Universal Adiabatic Quantum Computers

It has been established that local lattice spin Hamiltonians can be used for universal adiabatic quantum computation. However, the 2-local model Hamiltonians used in these proofs are general and hence do not limit the types of interactions required between spins. To address this concern, the present paper provides two simple model Hamiltonians that are of practical interest to experimentalists working towards the realization of a universal adiabatic quantum computer. The model Hamiltonians presented are the simplest known QMA-complete 2-local Hamiltonians. The 2-local Ising model with 1-local transverse field which has been realized using an array of technologies, is perhaps the simplest quantum spin model but is unlikely to be universal for adiabatic quantum computation. We demonstrate that this model can be rendered universal and QMA-complete by adding a tunable 2-local transverse XX coupling. We also show the universality and QMA-completeness of spin models with only 1-local Z and X fields and 2-local ZX interactions.Comment: Paper revised and extended to improve clarity; to appear in Physical Review

A Deformable Model for Magnetic Vortex Pinning

A two-parameter analytical model of the magnetic vortex in a thin disk of soft magnetic material is constructed. The model is capable of describing the change in evolution of net vortex state magnetization and of core position when the vortex core interacts with a magnetic pinning site. The model employs a piecewise, physically continuous, magnetization distribution obtained by the merger of two extensively used one-parameter analytical models of the vortex state in a disk. Through comparison to numerical simulations of ideal disks with and without pinning sites, the model is found to accurately predict the magnetization, vortex position, hysteretic transitions, and 2-D displacement of the vortex in the presence of pinning sites. The model will be applicable to the quantitative determination of vortex pinning energies from measurements of magnetization.Comment: 27 pages, 7 figures, including supplementary information, ancillary files:3 supplementary movie

International Coordination of Economic Policies: Scope, Methods, and Effects

This paper discusses the scope, methods, the effects of international coordination of economic policies. In addressing the scope for and of coordination, the analysis covers the rationale for coordination, barriers to coordination, the range and specificity of policies to be coordinated, the frequency of coordination, and the size of the coordinating group. Turning to the methods of coordination, the emphasis is on the broad issues of rules versus discretion, single-indicator versus multi-indicator approaches, and hegemonic versus more symmetric systems. In an attempt to shed some light on the effects of alternative rule- based proposals for coordination, we present some simulations of a global macroeconomic model (MULTIMQD) developed in the International Monetary Fund. The simulations considered range from 'smoothing rules for monetary and fiscal policy that imply only minimal international coordination, to more activist "target-zone" proposals that place greater restrictions on national authorities in the conduct of monetary and/or fiscal policies. The simulation results are compared to the actual evolution of the world economy over the 1974-87 period. Our findings suggest that simple mechanistic rule-based proposals are unlikely to lead to improved performance.