4,467 research outputs found
Numerical Analysis of Boosting Scheme for Scalable NMR Quantum Computation
Among initialization schemes for ensemble quantum computation beginning at
thermal equilibrium, the scheme proposed by Schulman and Vazirani [L. J.
Schulman and U. V. Vazirani, in Proceedings of the 31st ACM Symposium on Theory
of Computing (STOC'99) (ACM Press, New York, 1999), pp. 322-329] is known for
the simple quantum circuit to redistribute the biases (polarizations) of qubits
and small time complexity. However, our numerical simulation shows that the
number of qubits initialized by the scheme is rather smaller than expected from
the von Neumann entropy because of an increase in the sum of the binary
entropies of individual qubits, which indicates a growth in the total classical
correlation. This result--namely, that there is such a significant growth in
the total binary entropy--disagrees with that of their analysis.Comment: 14 pages, 18 figures, RevTeX4, v2,v3: typos corrected, v4: minor
changes in PROGRAM 1, conforming it to the actual programs used in the
simulation, v5: correction of a typographical error in the inequality sign in
PROGRAM 1, v6: this version contains a new section on classical correlations,
v7: correction of a wrong use of terminology, v8: Appendix A has been added,
v9: published in PR
Entropic measures of individual mobility patterns
Understanding human mobility from a microscopic point of view may represent a
fundamental breakthrough for the development of a statistical physics for
cognitive systems and it can shed light on the applicability of macroscopic
statistical laws for social systems. Even if the complexity of individual
behaviors prevents a true microscopic approach, the introduction of mesoscopic
models allows the study of the dynamical properties for the non-stationary
states of the considered system. We propose to compute various entropy measures
of the individual mobility patterns obtained from GPS data that record the
movements of private vehicles in the Florence district, in order to point out
new features of human mobility related to the use of time and space and to
define the dynamical properties of a stochastic model that could generate
similar patterns. Moreover, we can relate the predictability properties of
human mobility to the distribution of time passed between two successive trips.
Our analysis suggests the existence of a hierarchical structure in the mobility
patterns which divides the performed activities into three different
categories, according to the time cost, with different information contents. We
show that a Markov process defined by using the individual mobility network is
not able to reproduce this hierarchy, which seems the consequence of different
strategies in the activity choice. Our results could contribute to the
development of governance policies for a sustainable mobility in modern cities
Expansion and evaporation of hot nuclei: Comparison between semi-classical and quantal mean-field approaches
We present a general discussion of the mean field dynamics of finite nuclei
prepared under extreme conditions of temperature and pressure. We compare the
prediction of semi-classical approximation with complete quantum simulations.
Many features of the dynamics are carefully studied such as the collective
expansion, the evaporation process, the different time-scale... This study
points out many quantitative differences between quantum and semi-classical
approaches. Part of the differences are related to numerical features inherent
in semi-classical simulations but most of them are a direct consequence of the
non treatment of nuclei as quantal objects. In particular, we show that because
of a too strong damping in semi-classical approaches the expansion of hot
nuclei is quenched and the speed of the collective motion reduced.Comment: 41 pages including 14 figure
Gamma-Ray Bursts via the Neutrino Emission from Heated Neutron Stars
A model is proposed for gamma-ray bursts based upon a neutrino burst of about
10^52 ergs lasting a few seconds above a heated collapsing neutron star. This
type of thermal neutrino burst is suggested by relativistic hydrodynamic
studies of the compression, heating, and collapse of close binary neutron stars
as they approach their last stable orbit, but may arise from other sources as
well. We present a hydrodynamic simulation of the formation and evolution of
the pair plasma associated with such a neutrino burst. This pair plasma leads
to the production of ~10^51 - 10^52 ergs in gamma-rays with spectral and
temporal properties consistent with observed gamma-ray bursts.Comment: Final version. 30 pages, 10 figures, 6 tables, accepted for
publication in The Astrophysical Journa
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