Fluctuations and energy relaxation in non-linear nano-electro-mechanical systems at low temperatures

LTL Quantum Physics Seminar (Nanotalo). Speaker: Dr. Olivier Maillet (Institut Néel, France).

Owing to tremendous progresses in nanofabrication over the last three decades, mechanical resonators have reached the nanometer scale. On the one hand, these nanomechanical systems can be thought of as very sensitive force/mass probes, while realizations of the quantum ground state of a macroscopic mechanical degree of freedom have highlighted their potential as model systems for fundamental physics. One feature of interest for both applied and fundamental purposes is their sensitivity to external perturbations:  sensing applications require a good stability with minimal losses and frequency fluctuations, the latter leading to pure dephasing. Yet, more fundamentally, many intrinsic mechanisms leading to mechanical energy dissipation and frequency fluctuations in these vibrating nanostructures are still poorly known.
We will introduce first an experimental study of beam-based nano-electro-mechanical systems (NEMS) at helium temperatures which aims at separating damping and (classical) pure dephasing processes. We will emphasize on a fundamental dephasing mechanism originating from transduction of the NEMS’ Brownian motion into a colored, non-Gaussian frequency noise mediated by the NEMS geometric non-linearities. Measurements agree well with a theoretical model that takes into account the competition between the response's phase diffusion and the decay of frequency noise correlations. Then we will present our recent attempts to experimentally address microscopic mechanical losses and frequency fluctuations mechanisms at millikelvin temperatures, which are thought to originate from interactions between phonons or conduction electrons and tunneling two-level-systems in the disordered matter constituting the NEMS.