2,160 research outputs found
Quantum Stirring in low dimensional devices
A circulating current can be induced in the Fermi sea by displacing a
scatterer, or more generally by integrating a quantum pump into a closed
circuit. The induced current may have either the same or the opposite sense
with respect to the "pushing" direction of the pump. We work out explicit
expressions for the associated geometric conductance using the Kubo-Dirac
monopoles picture, and illuminate the connection with the theory of adiabatic
passage in multiple path geometry.Comment: 6 pages, 5 figures, improved versio
Towards realistic implementations of a Majorana surface code
Surface codes have emerged as promising candidates for quantum information
processing. Building on the previous idea to realize the physical qubits of
such systems in terms of Majorana bound states supported by topological
semiconductor nanowires, we show that the basic code operations, namely
projective stabilizer measurements and qubit manipulations, can be implemented
by conventional tunnel conductance probes and charge pumping via
single-electron transistors, respectively. The simplicity of the access scheme
suggests that a functional code might be in close experimental reach.Comment: 5 pages, 1 p. suppl.mat, PRL in pres
The Averaged Periodogram Estimator for a Power Law in Coherency
We prove the consistency of the averaged periodogram estimator (APE) in
two new cases. First, we prove that the APE is consistent for negative
memory parameters, after suitable tapering. Second, we prove that the
APE is consistent for a power law in the cross-spectrum and therefore
for a power law in the coherency, provided that sufficiently many
frequencies are used in estimation. Simulation evidence suggests that
the lower bound on the number of frequencies is a necessary condition
for consistency. For a Taylor series approximation to the estimator of
the power law in the cross-spectrum, we consider the rate of
convergence, and obtain a central limit theorem under suitable
regularity conditions.J.P. Morgan Chase and Co. and New York UniversityStatistics Working Papers Serie
Computationally Efficient Gaussian Maximum Likelihood Methods for Vector ARFIMA Models
In this paper, we discuss two distinct multivariate time series models that extend the univariate ARFIMA model. We describe algorithms for computing the covariances of each model, for computing the quadratic form and approximating the determinant for maximum likelihood estimation, and for simulating from each model. We compare the speed and accuracy of each algorithm to existing methods and measure the performance of the maximum likelihood estimator compared to existing methods. We also fit models to data on unemployment and inflation in the United States, to data on goods and services inflation in the United States, and to data about precipitation in the Great Lakes.Statistics Working Papers Serie
Local Magnetization in the Boundary Ising Chain at Finite Temperature
We study the local magnetization in the 2-D Ising model at its critical
temperature on a semi-infinite cylinder geometry, and with a nonzero magnetic
field applied at the circular boundary of circumference . This model
is equivalent to the semi-infinite quantum critical 1-D transverse field Ising
model at temperature , with a symmetry-breaking field
applied at the point boundary. Using conformal field theory methods
we obtain the full scaling function for the local magnetization analytically in
the continuum limit, thereby refining the previous results of Leclair, Lesage
and Saleur in Ref. \onlinecite{Leclair}. The validity of our result as the
continuum limit of the 1-D lattice model is confirmed numerically, exploiting a
modified Jordan-Wigner representation. Applications of the result are
discussed.Comment: 9 pages, 3 figure
Electron Pair Resonance in the Coulomb Blockade
We study many-body corrections to the cotunneling current via a localized
state with energy at large bias voltages . We show that the
transfer of {\em electron pairs}, enabled by the Coulomb repulsion in the
localized level, results in ionization resonance peaks in the third derivative
of the current with respect to , centered at . Our
results predict the existence of previously unnoticed structure within
Coulomb-blockade diamonds.Comment: 5 pages, 4 figure
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