1,106 research outputs found
The social constitution of Information Technology policies in developing countries
The role of information, communication and knowledge in shaping socio-economic development has become a top concern for African countries. Information technology, however, does not only impose change on industry and market structures, but also changes the political and social structures of a country. Therefore, the development of information technology policies cannot ignore the practices of social agents within society. The user of the information and the information technology cannot be eliminated from the equation. If this is the case, the social agent becomes irrelevant. Current initiatives, however, with regard to the implementation of new information technologies in Africa, are mainly guided by techno-economical aspects, while the target groupâs socio-cultural context is hardly taken into account. This result in inappropriate technology, ignorance of the African user and a reinforcement of western elitism. It is the aim of this research to investigate IT policies within developing countries and to suggest a framework for the social constitution of such policies
Analysis of shot noise suppression in mesoscopic cavities in a magnetic field
We present a numerical investigation of shot noise suppression in mesoscopic
cavities and an intuitive semiclassical explanation of the behavior observed in
the presence of an orthogonal magnetic field. In particular, we conclude that
the decrease of shot noise for increasing magnetic field is the result of the
interplay between the diameter of classical cyclotron orbits and the width of
the apertures defining the cavity. Good agreement with published experimental
results is obtained, without the need of introducing fitting parameters.Comment: 5 pages, 3 figures, contents changed (final version
Positive Cross Correlations in a Normal-Conducting Fermionic Beam Splitter
We investigate a beam splitter experiment implemented in a normal conducting
fermionic electron gas in the quantum Hall regime. The cross-correlations
between the current fluctuations in the two exit leads of the three terminal
device are found to be negative, zero or even positive depending on the
scattering mechanism within the device. Reversal of the cross-correlations sign
occurs due to interaction between different edge-states and does not reflect
the statistics of the fermionic particles which `antibunch'.Comment: 4 pages, 4 figure
Dynamic generation of orbital quasiparticle entanglement in mesoscopic conductors
We propose a scheme for dynamically creating orbitally entangled
electron-hole pairs through a time-dependent variation of the electrical
potential in a mesoscopic conductor. The time-dependent potential generates a
superposition of electron-hole pairs in two different orbital regions of the
conductor, a Mach-Zehnder interferometer in the quantum Hall regime. The
orbital entanglement is detected via violation of a Bell inequality, formulated
in terms of zero-frequency current noise. Adiabatic cycling of the potential,
both in the weak and strong amplitude limit, is considered.Comment: 4 pages, 2 figures; references update
Full counting statistics of chaotic cavities with many open channels
Explicit formulas are obtained for all moments and for all cumulants of the
electric current through a quantum chaotic cavity attached to two ideal leads,
thus providing the full counting statistics for this type of system. The
approach is based on random matrix theory, and is valid in the limit when both
leads have many open channels. For an arbitrary number of open channels we
present the third cumulant and an example of non-linear statistics.Comment: 4 pages, no figures; v2-added references; typos correcte
Semiclassical structure of chaotic resonance eigenfunctions
We study the resonance (or Gamow) eigenstates of open chaotic systems in the
semiclassical limit, distinguishing between left and right eigenstates of the
non-unitary quantum propagator, and also between short-lived and long-lived
states. The long-lived left (right) eigenstates are shown to concentrate as
on the forward (backward) trapped set of the classical dynamics.
The limit of a sequence of eigenstates is found
to exhibit a remarkably rich structure in phase space that depends on the
corresponding limiting decay rate. These results are illustrated for the open
baker map, for which the probability density in position space is observed to
have self-similarity properties.Comment: 4 pages, 4 figures; some minor corrections, some changes in
presentatio
Shot noise of series quantum point contacts intercalating chaotic cavities
Shot noise of series quantum point contacts forming a sequence of cavities in
a two dimensional electron gas are studied theoretically and experimentally.
Noise in such a structure originates from local scattering at the point
contacts as well as from chaotic motion of the electrons in the cavities. We
found that the measured shot noise is in reasonable agreement with our
theoretical prediction taking the cavity noise into account.Comment: 4 pages, 5 figure
Quantum state tomography with quantum shotnoise
We propose a scheme for a complete reconstruction of one- and two-particle
orbital quantum states in mesoscopic conductors. The conductor in the transport
state continuously emits orbital quantum states. The orbital states are
manipulated by electronic beamsplitters and detected by measurements of average
currents and zero frequency current shotnoise correlators. We show how, by a
suitable complete set of measurements, the elements of the density matrices of
the one- and two-particle states can be directly expressed in terms of the
currents and current correlators.Comment: 4 pages, 2 figure
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