262 research outputs found
Evolution of a black hole-inhabited brane close to reconnection
Last moments of a mini black hole escaping from a brane are studied. It is
argued that at the point of reconnection, where the piece of the brane attached
to the black hole separates from the rest, the worldsheet of the brane becomes
isotropic (light-like). The degenerate mode of evolution, with the worldsheet
isotropic everywhere, is investigated. In particular, it is shown that the
brane approaches the reconnection point from below if it reconnects within a
certain limit distance, and from above if it reconnects beyond that distance.
The rate of relaxation to the degenerate mode is established. If the dimension
of the brane is , the nondegeneracy, measured by the determinant of the
relevant part of the induced metric tensor, falls down as (latitudinal
angle).Comment: 20 pages, 4 figure
Multi-Particle Universal Processes
We generalize bipartite universal processes to the subclass of multi-particle universal processes from one to N particles. We show how the general statement for a multi-particle universal process can be constructed. The one-parameter family of processes generating totally anti-symmetric states has been generalized to a multi-particle regime and its entanglement properties have been studied. A view is given on the complete positivity and the possible physical realization of universal processes.
Simple models suffice for the single dot quantum shuttle
A quantum shuttle is an archetypical nanoelectromechanical device, where the
mechanical degree of freedom is quantized. Using a full-scale numerical
solution of the generalized master equation describing the shuttle, we have
recently shown [Novotn\'{y} {\it et al.}, Phys. Rev. Lett. {\bf 92}, 248302
(2004)] that for certain limits of the shuttle parameters one can distinguish
three distinct charge transport mechanisms: (i) an incoherent tunneling regime,
(ii) a shuttling regime, where the charge transport is synchronous with the
mechanical motion, and (iii) a coexistence regime, where the device switches
between the tunneling and shuttling regimes. While a study of the cross-over
between these three regimes requires the full numerics, we show here that by
identifying the appropriate time-scales it is possible to derive vastly simpler
equations for each of the three regimes. The simplified equations allow a clear
physical interpretation, are easily solved, and are in good agreement with the
full numerics in their respective domains of validity.Comment: 23 pages, 14 figures, invited paper for the Focus issue of the New
Journal of Physics on Nano-electromechanical system
Full counting statistics of nano-electromechanical systems
We develop a theory for the full counting statistics (FCS) for a class of
nanoelectromechanical systems (NEMS), describable by a Markovian generalized
master equation. The theory is applied to two specific examples of current
interest: vibrating C60 molecules and quantum shuttles. We report a numerical
evaluation of the first three cumulants for the C60-setup; for the quantum
shuttle we use the third cumulant to substantiate that the giant enhancement in
noise observed at the shuttling transition is due to a slow switching between
two competing conduction channels. Especially the last example illustrates the
power of the FCS.Comment: 7 pages, 3 figures; minor changes - final version as published in
Europhys. Let
The influence of charge detection on counting statistics
We consider the counting statistics of electron transport through a double
quantum dot with special emphasis on the dephasing induced by a nearby charge
detector. The double dot is embedded in a dissipative enviroment, and the
presence of electrons on the double dot is detected with a nearby quantum point
contact. Charge transport through the double dot is governed by a non-Markovian
generalized master equation. We describe how the cumulants of the current can
be obtained for such problems, and investigate the difference between the
dephasing mechanisms induced by the quantum point contact and the coupling to
the external heat bath. Finally, we consider various open questions of
relevance to future research.Comment: 15 pages, 2 figures, Contribution to 5-th International Conference on
Unsolved Problems on Noise, Lyon, France, June 2-6, 200
On the 3D steady flow of a second grade fluid past an obstacle
We study steady flow of a second grade fluid past an obstacle in three space
dimensions. We prove existence of solution in weighted Lebesgue spaces with
anisotropic weights and thus existence of the wake region behind the obstacle.
We use properties of the fundamental Oseen tensor together with results
achieved in \cite{Koch} and properties of solutions to steady transport
equation to get up to arbitrarily small \ep the same decay as the Oseen
fundamental solution
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