Noise and high frequency
Noise and high frequency measurement techniques
The dominating noise mechanism in mesoscopic samples at low temperatures is shot noise. In some cases, it is the limiting factor for the measurement sensitivity, but shot noise itself may be the actual quantity of interest as it, contrary to the thermal noise, contains information about the sample, complement to that of the average current.
Many of the interesting predictions for noise have been obtained for nonlinear elements (with voltage-dependent response) whose resistance is typically in the range of kΩ or more. However, measurement of shot noise in such samples is not always straightforward as the excess noise added by the amplifiers depends on the sample impedance, and thus on the applied voltage.
We are presently interested in shot noise experiments as well as measurements of the third moment of current fluctuations in a variety of mesoscopic systems. To access these these quantities in samples with large impedance requires matching circuits and extra measures in order to preserve the information within the accessible band width. In addition, we are working on the noise optimization of read-out electronics for qubits. One candidate for fast read-out purposes is the RF-SET, an amplitude modulated single electron transistor (SET) that is the fastest and the most sensitive electrometer known today.