160,834 research outputs found
Process tomography via sequential measurements on a single quantum system
We utilize a discrete (sequential) measurement protocol to investigate
quantum process tomography of a single two-level quantum system, with an
unknown initial state, undergoing Rabi oscillations. The ignorance of the
dynamical parameters is encoded into a continuous-variable classical system
which is coupled to the two-level quantum system via a generalized Hamiltonian.
This combined estimate of the quantum state and dynamical parameters is updated
by using the information obtained from sequential measurements on the quantum
system and, after a sufficient waiting period, faithful state monitoring and
parameter determination is obtained. Numerical evidence is used to demonstrate
the convergence of the state estimate to the true state of the hybrid system.Comment: 7 pages, 2 figure
Nonlinear State-Space Models for Microeconometric Panel Data
In applied microeconometric panel data analyses, time-constant random effects and first-order Markov chains are the most prevalent structures to account for intertemporal correlations in limited dependent variable models. An example from health economics shows that the addition of a simple autoregressive error terms leads to a more plausible and parsimonious model which also captures the dynamic features better. The computational problems encountered in the estimation of such models - and a broader class formulated in the framework of nonlinear state space models - hampers their widespread use. This paper discusses the application of different nonlinear filtering approaches developed in the time-series literature to these models and suggests that a straightforward algorithm based on sequential Gaussian quadrature can be expected to perform well in this setting. This conjecture is impressively confirmed by an extensive analysis of the example application
Nonparametric estimation of the fragmentation kernel based on a PDE stationary distribution approximation
We consider a stochastic individual-based model in continuous time to
describe a size-structured population for cell divisions. This model is
motivated by the detection of cellular aging in biology. We address here the
problem of nonparametric estimation of the kernel ruling the divisions based on
the eigenvalue problem related to the asymptotic behavior in large population.
This inverse problem involves a multiplicative deconvolution operator. Using
Fourier technics we derive a nonparametric estimator whose consistency is
studied. The main difficulty comes from the non-standard equations connecting
the Fourier transforms of the kernel and the parameters of the model. A
numerical study is carried out and we pay special attention to the derivation
of bandwidths by using resampling
Measurability of kinetic temperature from metal absorption-line spectra formed in chaotic media
We present a new method for recovering the kinetic temperature of the
intervening diffuse gas to an accuracy of 10%. The method is based on the
comparison of unsaturated absorption-line profiles of two species with
different atomic weights. The species are assumed to have the same temperature
and bulk motion within the absorbing region. The computational technique
involves the Fourier transform of the absorption profiles and the consequent
Entropy-Regularized chi^2-Minimization [ERM] to estimate the model parameters.
The procedure is tested using synthetic spectra of CII, SiII and FeII ions. The
comparison with the standard Voigt fitting analysis is performed and it is
shown that the Voigt deconvolution of the complex absorption-line profiles may
result in estimated temperatures which are not physical. We also successfully
analyze Keck telescope spectra of CII1334 and SiII1260 lines observed at the
redshift z = 3.572 toward the quasar Q1937--1009 by Tytler {\it et al.}.Comment: 25 pages, 6 Postscript figures, aaspp4.sty file, submit. Ap
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