377,776 research outputs found
Dephasing of a superconducting flux qubit
In order to gain a better understanding of the origin of decoherence in
superconducting flux qubits, we have measured the magnetic field dependence of
the characteristic energy relaxation time () and echo phase relaxation
time () near the optimal operating point of a flux qubit. We
have measured by means of the phase cycling method. At the
optimal point, we found the relation . This means
that the echo decay time is {\it limited by the energy relaxation} (
process). Moving away from the optimal point, we observe a {\it linear}
increase of the phase relaxation rate () with the applied
external magnetic flux. This behavior can be well explained by the influence of
magnetic flux noise with a spectrum on the qubit
Dephasing of a superconducting flux qubit
In order to gain a better understanding of the origin of decoherence in
superconducting flux qubits, we have measured the magnetic field dependence of
the characteristic energy relaxation time () and echo phase relaxation
time () near the optimal operating point of a flux qubit. We
have measured by means of the phase cycling method. At the
optimal point, we found the relation . This means
that the echo decay time is {\it limited by the energy relaxation} (
process). Moving away from the optimal point, we observe a {\it linear}
increase of the phase relaxation rate () with the applied
external magnetic flux. This behavior can be well explained by the influence of
magnetic flux noise with a spectrum on the qubit
Delay Estimator and Improved Proportionate Multi-Delay Adaptive Filtering Algorithm
This paper pertains to speech and acoustic signal processing, and particularly to a determination of echo path delay and operation of echo cancellers. To cancel long echoes, the number of weights in a conventional adaptive filter must be large. The length of the adaptive filter will directly affect both the degree of accuracy and the convergence speed of the adaptation process. We present a new adaptive structure which is capable to deal with multiple dispersive echo paths. An adaptive filter according to the present invention includes means for storing an impulse response in a memory, the impulse response being indicative of the characteristics of a transmission line. It also includes a delay estimator for detecting ranges of samples within the impulse response having relatively large distribution of echo energy. These ranges of samples are being indicative of echoes on the transmission line. An adaptive filter has a plurality of weighted taps, each of the weighted taps having an associated tap weight value. A tap allocation/control circuit establishes the tap weight values in response to said detecting means so that only taps within the regions of relatively large distributions of echo energy are turned on. Thus, the convergence speed and the degree of estimation in the adaptation process can be improved
Neurophysiological analysis of echolocation in bats
An analysis of echolocation and signal processing in brown bats is presented. Data cover echo detection, echo ranging, echolocalization, and echo analysis. Efforts were also made to identify the part of the brain that carries out the most essential processing function for echolocation. Results indicate the inferior colliculus and the auditory nuclei function together to process this information
Echo spectroscopy of bulk Bogoliubov excitations in trapped Bose-Einstein condensates
We propose and demonstrate an echo method to reduce the inhomogeneous
linewidth of Bogoliubov excitations, in a harmonically-trapped Bose-Einstein
condensate. Our proposal includes the transfer of excitations with momentum +q
to -q using a double two photon Bragg process, in which a substantial reduction
of the inhomogeneous broadening is calculated. Furthermore, we predict an
enhancement in the method's efficiency for low momentum due to many-body
effects. The echo can also be implemented by using a four photon process, as is
demonstrated experimentally.Comment: 4 pages, 5 figure
Power cepstrum technique with application to model helicopter acoustic data
The application of the power cepstrum to measured helicopter-rotor acoustic data is investigated. A previously applied correction to the reconstructed spectrum is shown to be incorrect. For an exact echoed signal, the amplitude of the cepstrum echo spike at the delay time is linearly related to the echo relative amplitude in the time domain. If the measured spectrum is not entirely from the source signal, the cepstrum will not yield the desired echo characteristics and a cepstral aliasing may occur because of the effective sample rate in the frequency domain. The spectral analysis bandwidth must be less than one-half the echo ripple frequency or cepstral aliasing can occur. The power cepstrum editing technique is a useful tool for removing some of the contamination because of acoustic reflections from measured rotor acoustic spectra. The cepstrum editing yields an improved estimate of the free field spectrum, but the correction process is limited by the lack of accurate knowledge of the echo transfer function. An alternate procedure, which does not require cepstral editing, is proposed which allows the complete correction of a contaminated spectrum through use of both the transfer function and delay time of the echo process
Nuclear spin-spin coupling in La_{2-x}Sr_{x}CuO_{4} studied by stimulated echo decay
We have performed copper NQR experiments in high temperature superconductors
YBa_{2}Cu_{4}O_{8}, YBa_{2}Cu_{3}O_{7}, and La_{2-x}Sr_{x}CuO_{4} (x=0.12 and
0.15), using the stimulated echo technique. The stimulated echo intensity is
analyzed by a model that includes the spin-lattice relaxation process (T_ {1
}-process) and the fluctuating local field due to nuclear spin-spin coupling.
The model gives quantitative account of the experimental results in Y-based
compounds using the known values of 1/T_{1} and 1/T_{2G}, the gaussian decay
rate of the spin echo intensity. The same model applied to LSCO enables us to
extract the value of T_{2G}. Our results indicate that T_{1}T/T_{2G} is
independent of temperature, implying that the dynamic exponent is one in
La_{2-x}Sr_{x}CuO_{4}.Comment: 14 pages, 11 fugures, The bibliography field is correcte
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