5,906 research outputs found
Algebraic fidelity decay for local perturbations
From a reflection measurement in a rectangular microwave billiard with
randomly distributed scatterers the scattering and the ordinary fidelity was
studied. The position of one of the scatterers is the perturbation parameter.
Such perturbations can be considered as {\em local} since wave functions are
influenced only locally, in contrast to, e. g., the situation where the
fidelity decay is caused by the shift of one billiard wall. Using the
random-plane-wave conjecture, an analytic expression for the fidelity decay due
to the shift of one scatterer has been obtained, yielding an algebraic
decay for long times. A perfect agreement between experiment and theory has
been found, including a predicted scaling behavior concerning the dependence of
the fidelity decay on the shift distance. The only free parameter has been
determined independently from the variance of the level velocities.Comment: 4 pages, 5 figure
Distribution of the S-matrix in chaotic microwave cavities with direct processes and absorption
We quantify the presence of direct processes in the S-matrix of chaotic
microwave cavities with absorption in the one-channel case. To this end the
full distribution P_S(S) of the S-matrix, i.e. S=\sqrt{R}e^{i\theta}, is
studied in cavities with time-reversal symmetry for different antenna coupling
strengths T_a or direct processes. The experimental results are compared with
random-matrix calculations and with numerical simulations based on the
Heidelberg approach including absorption. The theoretical result is a
generalization of the Poisson kernel. The experimental and the numerical
distributions are in excellent agreement with random-matrix predictions for all
cases.Comment: 4 pages, 4 figure
Weyl asymptotics: From closed to open systems
We present microwave experiments on the symmetry reduced 5-disk billiard
studying the transition from a closed to an open system. The measured microwave
reflection signal is analyzed by means of the harmonic inversion and the
counting function of the resulting resonances is studied. For the closed system
this counting function shows the Weyl asymptotic with a leading exponent equal
to 2. By opening the system successively this exponent decreases smoothly to an
non-integer value. For the open systems the extraction of resonances by the
harmonic inversion becomes more challenging and the arising difficulties are
discussed. The results can be interpreted as a first experimental indication
for the fractal Weyl conjecture for resonances.Comment: 9 pages, 7 figure
Scanning Fourier Spectroscopy: A microwave analog study to image transmission paths in quantum dots
We use a microwave cavity to investigate the influence of a movable absorbing
center on the wave function of an open quantum dot. Our study shows that the
absorber acts as a position-selective probe, which may be used to suppress
those wave function states that exhibit an enhancement of their probability
density near the region where the impurity is located. For an experimental
probe of this wave function selection, we develop a technique that we refer to
as scanning Fourier spectroscopy, which allows us to identify, and map out, the
structure of the classical trajectories that are important for transmission
through the cavity.Comment: 4 pages, 5 figure
Signatures of Dynamical Tunneling in the Wave function of a Soft-Walled Open Microwave Billiard
Evidence for dynamical tunneling is observed in studies of the transmission,
and wave functions, of a soft-walled microwave cavity resonator. In contrast to
previous work, we identify the conditions for dynamical tunneling by monitoring
the evolution of the wave function phase as a function of energy, which allows
us to detect the tunneling process even under conditions where its expected
level splitting remains irresolvable.Comment: 5 pages, 5 figure
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Combustion of Shock-Dispersed Flake Aluminum - High-Speed Visualization
Charges of 0.5 g PETN were used to disperse 1 g of flake aluminum in a rectangular test chamber of 4 liter inner volume and inner dimensions of approximately 10 cm x 10 cm x 40 cm. The subsequent combustion of the flake aluminum with the ambient air in the chamber gave rise to a highly luminous flame. The evolution of the luminous region was studied by means of high-speed cinematography. The high-speed camera is responsive to a broad spectral range in the visible and near infra-red. For a number of tests this response range was narrowed down by means of a band-pass filter with a center wavelength of 488 nm and a half-width of 23 nm. The corresponding images were expected to have a stronger temperature dependence than images obtained without the filter, thus providing better capability to highlight hot-spots. Emission in the range of the pass-band of the filter can be due to continuous thermal radiation from hot Al and Al{sub 2}O{sub 3} particles or to molecular band emission from gaseous AlO. A time-resolving spectrometer was improvised to inspect this topic. The results suggest that AlO emission occurs, but that the continuous spectrum is the dominating effect in our experiments
Synthesis and investigation of the spectral-luminescence characteristics of powder based on zinc oxide
ZnO and ZnAlO composites were synthesized by thermal decomposition of a precursor salt, dried at 200 °C and annealed at 400 and 600 °C, respectively. It was shown that pH and temperature of synthesis has great influence on the spectral-luminescence properties of samples
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