1,310 research outputs found
Sound for enhanced experiences in mobile applications
When visiting new places you want information about restaurants, shopping, places of historic in- terest etc. Smartphones are perfect tools for de- livering such location-based information, but the risk is that users get absorbed by texts, maps, videos etc. on the device screen and get a second- hand experience of the environment they are vis- iting rather than the sought-after first-hand expe- rience.
One problem is that the users’ eyes often are directed to the device screen, rather than to the surrounding environment. Another problem is that interpreting more or less abstract informa- tion on maps, texts, images etc. may take up sig- nificant shares of the users’ overall cognitive re- sources.
The work presented here tried to overcome these two problems by studying design for human-computer interaction based on the users’ everyday abilities such as directional hearing and point and sweep gestures. Today’s smartphones know where you are, in what direction you are pointing the device and they have systems for ren- dering spatial audio. These readily available tech- nologies hold the potential to make information more easy to interpret and use, demand less cog- nitive resources and free the users from having to look more or less constantly on a device screen
Negative-resistance models for parametrically flux-pumped superconducting quantum interference devices
A Superconducting QUantum Interference Device (SQUID) modulated by a fast
oscillating magnetic flux can be used as a parametric amplifier, providing gain
with very little added noise. Here, we develop linearized models to describe
the parametrically flux-pumped SQUID in terms of an impedance. An unpumped
SQUID acts as an inductance, the Josephson inductance, whereas a flux-pumped
SQUID develops an additional, parallel element which we have coined the
``pumpistor.'' Parametric gain can be understood as a result of a negative
resistance of the pumpistor. In the degenerate case, the gain is sensitive to
the relative phase between the pump and signal. In the nondegenerate case, gain
is independent of this phase.
We develop our models first for degenerate parametric pumping in the
three-wave and four-wave cases, where the pump frequency is either twice or
equal to the signal frequency, respectively. We then derive expressions for the
nondegenerate case where the pump frequency is not a multiple of the signal
frequency, where it becomes necessary to consider idler tones which develop.
For the nondegenerate three-wave case, we present an intuitive picture for a
parametric amplifier containing a flux-pumped SQUID where current at the signal
frequency depends upon the load impedance at an idler frequency. This
understanding provides insight and readily testable predictions of circuits
containing flux-pumped SQUIDs.Comment: 27 pages, 6 figures, 1 tabl
Direct observation of time correlated single-electron tunneling
We report a direct detection of time correlated single-electron tunneling
oscillations in a series array of small tunnel junctions. Here the current, I,
is made up of a lattice of charge solitons moving throughout the array by time
correlated tunneling with the frequency f=I/e, where e is the electron charge.
To detect the single charges, we have integrated the array with a
radio-frequency single-electron transistor (RF-SET) and employed two different
methods to couple the array to the SET input: by direct injection through a
tunnel junction, and by capacitive coupling. In this paper we report the
results from the latter type of charge input, where we have observed the
oscillations in the frequency domain and measured currents from 50 to 250 fA by
means of electron counting.Comment: 2 pages, 1 figure; submitted to the 10th International
Superconductive Electronics Conference (ISEC'05), the Netherlands, Sept. 200
Line Widths of Single-Electron Tunneling Oscillations: Experiment and Numerical Simulations
We present experimental and numerical results from a real-time detection of
time-correlated single-electron tunneling oscillations in a one-dimensional
series array of small tunnel junctions. The electrons tunnel with a frequency
f=I/e, where I is the current and e is the electron charge. Experimentally, we
have connected a single-electron transistor to the last array island, and in
this way measured currents from 5 fA to 1 pA by counting the single electrons.
We find that the line width of the oscillation is proportional to the frequency
f. The experimental data agrees well with numerical simulations.Comment: 2 pages, 1 figure. Submitted to the 24th International Conference on
Low Temperature Physics (LT24), Orlando, FL, USA, Aug. 2005; to be published
in the AIP Conference Proceedings serie
Designing frequency-dependent relaxation rates and Lamb shift for a giant artificial atom
In traditional quantum optics, where the interaction between atoms and light
at optical frequencies is studied, the atoms can be approximated as point-like
when compared to the wavelength of light. So far, this relation has also been
true for artificial atoms made out of superconducting circuits or quantum dots,
interacting with microwave radiation. However, recent and ongoing experiments
using surface acoustic waves show that a single artificial atom can be coupled
to a bosonic field at several points wavelengths apart. Here, we theoretically
study this type of system. We find that the multiple coupling points give rise
to a frequency dependence in the coupling strength between the atom and its
environment, and also in the Lamb shift of the atom. The frequency dependence
is given by the discrete Fourier transform of the coupling point coordinates
and can therefore be designed. We discuss a number of possible applications for
this phenomenon, including tunable coupling, single-atom lasing, and other
effects that can be achieved by designing the relative coupling strengths of
different transitions in a multi-level atom.Comment: 14 pages, 8 figure
Coulomb blockade thermometry using a two-dimensional array of tunnel junctions
We have measured current-voltage characteristics of two-dimensional arrays of
small tunnel junctions at temperatures from 1.5 K to 4.2 K. This corresponds to
thermal energies larger than the charging energy. We show that 2D-arrays can be
used as primary thermometers in the same way as 1D-arrays, and even have some
advantages over 1D-arrays. We have carried out Monte Carlo simulations, which
agree with our experimental results.Comment: 4 pages, 4 eps figures. Also available from Journal of Applied
Physics (http://link.aip.org/link/?jap/86/3844
A fast, primary Coulomb blockade thermometer
We have measured the third derivative of the current-voltage characteristics,
d^3I/dV^3, in a two-dimensional array of small tunnel junctions using a lock-in
amplifier. We show that this derivative is zero at a voltage which scales
linearly with the temperature and depends only on the temperature and natural
constants, thus providing a primary thermometer. We demonstrate a measurement
method which extracts the zero crossing voltage directly using a feedback
circuit. This method requires only one voltage measurement, which makes it
substantially faster than the original Coulomb blockade thermometry method.Comment: 3 pages, 4 figures. This article has been submitted to Applied
Physics Letters (http://ojps.aip.org/aplo
Bias and temperature dependence of the noise in a single electron transistor
A single electron transistor based on Al-AlO_x-Nb tunnel junctions was
fabricated by shadow evaporation and in situ barrier formation. Its output
current noise was measured, using a transimpedance amplifier setup, as a
function of bias voltage, gain, and temperature, in the frequency range 1...300
Hz. The spot noise at 10 Hz is dominated by a gain dependent component,
indicating that the main noise contribution comes from fluctuations at the
input of the transistor. Deviations from ideal input charge noise behaviour are
found in the form of a bias dependence of the differential charge equivalent
noise, i. e. the derivative of current noise with respect to gain. The
temperature dependence of this effect could indicate that heating is activating
the noise sources, and that they are located inside or in the near vicinity of
the junctions.Comment: 16 pages, 9 figures (EPS
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