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Physics at GHz frequencies ...
... fast and sensitive measurement techniques in solid state physics (and in other fields)
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Microwave Techniques for Experiments with Mesoscopic
Devices
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Research on mesoscopic devices, such as quantum dots, nanotubes,
nanowires, micro or nano mechnical systems etc. does benefit
enormously from the use of RF and microwave measurement
techniques. Probing ac-properties of such systems, the measurement
bandwidth is increased drastically, enabling experiments on
shorter time scales with larger signal to noise ratios than in
traditional dc- or low frequency transport measurements. Coupling
sub-micron or nano-scale devices, that typically have high
impedances and large wiring stray capacitances limiting the
measurement bandwidth, to a high frequency resonant circuit, such
as a cavity or a lumped LC circuit, allows one to probe the
conductance, capacitance or inductance of the device at microwave
frequencies. For example, the ground state properties and the
excitation spectrum of quantum dots or nanotubes can be inferred
from a susceptibility measurement instead of residing to dc
transport measurements. These measurements have the additional
advantage that capacitive or inductive coupling of the device
under test can be realized in a less perturbing way than by
attaching dc contacts to the device under test. We have
demonstrated the benefits of this technique in our circuit QED
experiments (A. Wallraff et al.) at frequencies in the GHz-range. In
recent years, similar techniques have been demonstrated at lower
frequencies (e.g. the radio frequency single electron trsnsistor)
and are currently implemented in
some of the highest sensitivity measurements performed with
mesoscopic devices (e.g. in nano mechanical resonators).
These techniques also benefit
from the available low-noise cryogenic amplifier technologies,
which have very well characterized noise performance. In our lab,
use of such techniques will bring novel mesoscopic experiments on
short time scales at large signal to noise ratios into range.
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Andreas Wallraff
andreas.wallraff@phys.ethz.ch
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