Probing quantum and classical noise in nano circuits

Doktorsavhandling, 2014

This thesis presents measurements of classical and quantum noise in nano circuits. The first part of the thesis, covers extensive measurements on charge noise sources. Low-frequency charge noise with the power spectrum close to 1/ f (where f is the frequency) has been observed in a variety of systems. Despite the large theoretical and experimental efforts during the past three decades, the origin of this noise is still unknown. One of the best platforms to study this noise is the single electron transistor (SET) which is extremely sensitive to charge. We have exploited this unique charge sensitivity to probe the charge noise sources. We have measured the temperature and the bias dependence of the charge noise and concluded that the two-level fluctuators (TLFs) which cause the charge noise have a temperature which is closer to the temperature of the electrons on the SET rather than to the temperature of the phonos underneath the SET. This suggests that most probably the charge noise sources are in the vicinity of the SET and can ther- malize with SET electrons through quantum tunneling which limits their distribution to within a few nanometers around the SET. In another set of measurements, we have probed the TLFs when they are pushed out of equilibrium by an external electric field. The relaxation process of the TLFs causes a charge drift which we have measured using a SET over four decades of time. We found that this drift is logarithmic in time and by comparing it to theory we could extract the density of TLFs. Studying how the drift depends on temperature and electric field, we can also conclude that the switching of the TLFs is due to quantum tunneling and not due to thermal activation. The second part of the thesis covers experiments related to vacuum fluctuations. Vacuum fluctuations are one of the most interesting predictions of the quantum me- chanics. We have demonstrated the first observation of the dynamical Casimir effect, which is generation of real photons out of the vacuum by modulation of a mirror at relativistic speeds. We show broad band generation of photons and demonstrate two-mode squeezing of this radiation. In another experiment, we have measured the strength of these vacuum fluctuations by using an artificial atom in front of a mirror as our quantum probe. In the last part of the thesis, we present preliminary results for characterization of the system consisting of two artificial atoms in front of a mirror, a system which can potentially exploited for studying the interaction of artificial atoms through exchange of photons.