1,771 research outputs found
An approach toward an analysis of the pattern recognition involved in the stellar orientation of birds
A conditioning method was used to investigate the orientational responses of ducks as affected by manipulations of the stellar patterns in a planetarium. Under simulated natural skies it was possible to train a bird to a particular direction successively under all positions of the rotating sphere at a constant latitude. The responses were independent of the phase relationships between local time, season, and appearance of the sky provided the bird had been trained under the particular sector of the sphere some time before
Shot noise of a quantum dot measured with GHz stub impedance matching
The demand for a fast high-frequency read-out of high impedance devices, such
as quantum dots, necessitates impedance matching. Here we use a resonant
impedance matching circuit (a stub tuner) realized by on-chip superconducting
transmission lines to measure the electronic shot noise of a carbon nanotube
quantum dot at a frequency close to 3 GHz in an efficient way. As compared to
wide-band detection without impedance matching, the signal to noise ratio can
be enhanced by as much as a factor of 800 for a device with an impedance of 100
k. The advantage of the stub resonator concept is the ease with which
the response of the circuit can be predicted, designed and fabricated. We
further demonstrate that all relevant matching circuit parameters can reliably
be deduced from power reflectance measurements and then used to predict the
power transmission function from the device through the circuit. The shot noise
of the carbon nanotube quantum dot in the Coulomb blockade regime shows an
oscillating suppression below the Schottky value of , as well an
enhancement in specific regions.Comment: 6 pages, 4 figures, supplementar
Josephson junction qubit network with current-controlled interaction
We design and evaluate a scalable charge qubit chain network with
controllable current-current coupling of neighbouring qubit loops via local
dc-current gates. The network allows construction of general N-qubit gates. The
proposed design is in line with current main stream experiments.Comment: 4 pages, 4 figure
Reversing quantum trajectories with analog feedback
We demonstrate the active suppression of transmon qubit dephasing induced by
dispersive measurement, using parametric amplification and analog feedback. By
real-time processing of the homodyne record, the feedback controller reverts
the stochastic quantum phase kick imparted by the measurement on the qubit. The
feedback operation matches a model of quantum trajectories with measurement
efficiency , consistent with the result obtained by
postselection. We overcome the bandwidth limitations of the amplification chain
by numerically optimizing the signal processing in the feedback loop and
provide a theoretical model explaining the optimization result.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures
Whispering Vortices
Experiments indicating the excitation of whispering gallery type
electromagnetic modes by a vortex moving in an annular Josephson junction are
reported. At relativistic velocities the Josephson vortex interacts with the
modes of the superconducting stripline resonator giving rise to novel
resonances on the current-voltage characteristic of the junction. The
experimental data are in good agreement with analysis and numerical
calculations based on the two-dimensional sine--Gordon model.Comment: 5 pages, 5 figures, text shortened to fit 4 pages, correction of
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Optimization of sample-chip design for stub-matched radio-frequency reflectometry measurements
A radio-frequency (rf) matching circuit with an in situ tunable varactor
diode used for rf reflectometry measurements in semiconductor nanostructures is
investigated and used to optimize the sample-specific chip design. The samples
are integrated in a 2-4 GHz stub-matching circuit consisting of a waveguide
stub shunted to the terminated coplanar waveguide. Several quantum point
contacts fabricated on a GaAs/AlGaAs heterostructure with different chip
designs are compared. We show that the change of the reflection coefficient for
a fixed change in the quantum point contact conductance can be enhanced by a
factor of 3 compared to conventional designs by a suitable electrode geometry
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