Quantum Device Lab

Circuit QED
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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

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.

Andreas Wallraff


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