1,692 research outputs found
Symbolic dynamics I. Finite dispersive billiards
Orbits in different dispersive billiard systems, e.g. the 3 disk system, are
mapped into a topological well ordered symbol plane and it is showed that
forbidden and allowed orbits are separated by a monotone pruning front. The
pruning front can be approximated by a sequence of finite symbolic dynamics
grammars.Comment: CYCLER Paper 93Jan00
Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects
Bulk silicon carbide (SiC) is a very promising material system for
bio-applications and quantum sensing. However, its optical activity lies beyond
the near infrared spectral window for in-vivo imaging and fiber communications
due to a large forbidden energy gap. Here, we report the fabrication of SiC
nanocrystals and isolation of different nanocrystal fractions ranged from 600
nm down to 60 nm in size. The structural analysis reveals further fragmentation
of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline
quality, separated by amorphization areas. We use neutron irradiation to create
silicon vacancies, demonstrating near infrared photoluminescence. Finally, we
detect, for the first time, room-temperature spin resonances of these silicon
vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use
them not only as in-vivo luminescent markers, but also as magnetic field and
temperature sensors, allowing for monitoring various physical, chemical and
biological processes.Comment: 5 pages, 4 figure
Resonance-Assisted Tunneling
We present evidence that tunneling processes in near-integrable systems are
enhanced due to the manifestation of nonlinear resonances and their respective
island chains in phase space. A semiclassical description of this
"resonance-assisted" mechanism is given, which is based on a local perturbative
description of the dynamics in the vicinity of the resonances. As underlying
picture, we obtain that the quantum state is coupled, via a succession of
classically forbidden transitions across nonlinear resonances, to high
excitations within the well, from where tunneling occurs with a rather large
rate. The connection between this description and the complex classical
structure of the underlying integrable dynamics is furthermore studied, giving
ground to the general coherence of the description as well as guidelines for
the identification of the dominant tunneling paths. The validity of this
mechanism is demonstrated within the kicked Harper model, where good agreement
between quantum and semiclassical (resonance-assisted) tunneling rates is
found.Comment: 52 pages, 16 figures, submitted to Annals of Physic
Local structure of self-affine sets
The structure of a self-similar set with open set condition does not change
under magnification. For self-affine sets the situation is completely
different. We consider planar self-affine Cantor sets E of the type studied by
Bedford, McMullen, Gatzouras and Lalley, for which the projection onto the
horizontal axis is an interval. We show that within small square neighborhoods
of almost each point x in E, with respect to many product measures on address
space, E is well approximated by product sets of an interval and a Cantor set.
Even though E is totally disconnected, the limit sets have the product
structure with interval fibres, reminiscent to the view of attractors of
chaotic differentiable dynamical systems.Comment: 10 pages, 2 figure
Symmetries and collective excitations in large superconducting circuits
The intriguing appeal of circuits lies in their modularity and ease of
fabrication. Based on a toolbox of simple building blocks, circuits present a
powerful framework for achieving new functionality by combining circuit
elements into larger networks. It is an open question to what degree modularity
also holds for quantum circuits -- circuits made of superconducting material,
in which electric voltages and currents are governed by the laws of quantum
physics. If realizable, quantum coherence in larger circuit networks has great
potential for advances in quantum information processing including topological
protection from decoherence. Here, we present theory suitable for quantitative
modeling of such large circuits and discuss its application to the fluxonium
device. Our approach makes use of approximate symmetries exhibited by the
circuit, and enables us to obtain new predictions for the energy spectrum of
the fluxonium device which can be tested with current experimental technology
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