55 research outputs found
Probing Localization in Absorbing Systems via Loschmidt Echos
We measure Anderson localization in quasi-one-dimensional waveguides in the
presence of absorption by analyzing the echo dynamics due to small
perturbations. We specifically show that the inverse participation number of
localized modes dictates the decay of the Loschmidt echo, differing from the
Gaussian decay expected for diffusive or chaotic systems. Our theory, based on
a random matrix modeling, agrees perfectly with scattering echo measurements on
a quasi one-dimensional microwave cavity filled with randomly distributed
scatterers.Comment: cross-reference with nonlin.CD-Chaotic Dynamic
Experimental Observation of Resonance-Assisted Tunneling
We present the first experimental observation of resonance-assisted
tunneling, a wave phenomenon, where regular-to-chaotic tunneling is strongly
enhanced by the presence of a classical nonlinear resonance chain. For this we
use a microwave cavity made of oxygen free copper with the shape of a
desymmetrized cosine billiard designed with a large nonlinear resonance chain
in the regular region. It is opened in a region, where only chaotic dynamics
takes place, such that the tunneling rate of a regular mode to the chaotic
region increases the line width of the mode. Resonance-assisted tunneling is
demonstrated by (i) a parametric variation and (ii) the characteristic plateau
and peak structure towards the semiclassical limit.Comment: 5 pages, 2 figure
Fidelity decay for local perturbations: microwave evidence for oscillating decay exponents
We study fidelity decay in classically chaotic microwave billiards for a local, piston-like boundary perturbation. We experimentally verify a predicted non-monotonic cross-over from the Fermi Golden Rule to the escape-rate regime of the Loschmidt echo decay with increasing local boundary perturbation. In particular, we observe pronounced oscillations of the decay rate as a function of the piston position which quantitatively agree with corresponding theoretical results based on a refined semiclassical approach for local boundary perturbations
Microwave experiments simulating quantum search and directed transport in artificial graphene
A series of quantum search algorithms have been proposed recently providing an algebraic speedup compared to classical search algorithms from N to \sqrt{N}, where N is the number of items in the search space. In particular, devising searches on regular lattices has become popular in extending Grover’s original algorithm to spatial searching. Working in a tight-binding setup, it could be demonstrated, theoretically, that a search is possible in the physically relevant dimensions 2 and 3 if the lattice spectrum possesses Dirac points. We present here a proof of principle experiment implementing wave search algorithms and directed wave transport in a graphene lattice arrangement. The idea is based on bringing localized search states into resonance with an extended lattice state in an energy region of low spectral density—namely, at or near the Dirac point. The experiment is implemented using classical waves in a microwave setup containing weakly coupled dielectric resonators placed in a honeycomb arrangement, i.e., artificial graphene. Furthermore, we investigate the scaling behavior experimentally using linear chains
Fano resonances and decoherence in transport through quantum dots
A tunable microwave scattering device is presented which allows the
controlled variation of Fano line shape parameters in transmission through
quantum billiards. We observe a non-monotonic evolution of resonance parameters
that is explained in terms of interacting resonances. The dissipation of
radiation in the cavity walls leads to decoherence and thus to a modification
of the Fano profile. We show that the imaginary part of the complex Fano
q-parameter allows to determine the absorption constant of the cavity. Our
theoretical results demonstrate further that the two decohering mechanisms,
dephasing and dissipation, are equivalent in terms of their effect on the
evolution of Fano resonance lineshapes.Comment: 9 pages, 7 figures, submitted to Physica E (conference proceedings
Синтез β-SiC из органо-неорганического комплекса (-СН₃)-(SiO₂)n-C в процессе службы периклазоуглеродистых огнеупоров на модифицированной кремнийорганикой фенолформальдегидной смоле
Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank
9 páginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved:
the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded
signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other
chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and
Conselleria de Pesca de la Xunta de GaliciaPeer reviewe
Microwave studies of the spectral statistics in chaotic systems
International audienceAn overview over the microwave studies of chaotic systems is presented, performed by the authors and their co-workers in Marburg and Nice. In an historical overview the impact of Fritz Haake in particular in the beginning of the experiments is recognized. In the following sections two subjects are presented he was particularly interested in. One of them is the Bohigas–Giannoni–Schmit conjecture stating that the universal features of the spectra of chaotic systems are well described by random matrix theory. Microwave realizations of seven of the ten universal ensembles have been achieved, starting with the Gaussian orthogonal ensemble in the very first experiment, and ending with the chiral ensembles in a recent work. To do the measurements the systems have to be opened by attaching antennas to excite the microwaves. Antennas are theoretically taken into account in terms of a non-Hermitian effective Hamiltonian with an imaginary part taking care of the coupling to the environment. Results on level spacing and widths distribution in open systems are presented as well as on resonance trapping observed when changing the coupling to the environment
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