150 research outputs found
A model of ideological struggle
A general model for opinion formation and competition, like in ideological
struggles is formulated. The underlying set is a closed one, like a country but
in which the population size is variable in time. Several ideologies compete to
increase their number of adepts. Such followers can be either converted from
one ideology to another or become followers of an ideology though being
previously ideologically-free. A reverse process is also allowed. We consider
two kinds of conversion: unitary conversion, e.g. by means of mass
communication tools, or binary conversion, e.g. by means of interactions
between people. It is found that the steady state,when it exists, depends on
the number of ideologies. Moreover when the number of ideologies increases some
tension arises between them. This tension can change in the course of time. We
propose to measure the ideology tensions through an appropriately defined scale
index.Comment: 10 pages, 3 figures, 46 references, working pape
Decoherence-free preparation of Dicke states of trapped ions by collective stimulated Raman adiabatic passage
We propose a simple technique for the generation of arbitrary-sized Dicke
states in a chain of trapped ions. The method uses global addressing of the
entire chain by two pairs of delayed but partially overlapping laser pulses to
engineer a collective adiabatic passage along a multi-ion dark state. Our
technique, which is a many-particle generalization of stimulated Raman
adiabatic passage (STIRAP), is decoherence-free with respect to spontaneous
emission and robust against moderate fluctuations in the experimental
parameters. Furthermore, because the process is very rapid, the effects of
heating are almost negligible under realistic experimental conditions. We
predict that the overall fidelity of synthesis of a Dicke state involving ten
ions sharing two excitations should approach 98% with currently achievable
experimental parameters.Comment: 14 pages, 8 figure
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