Nano-Electro-Mechanical Systems at Ultra Low Temperatures as Probes for Quantum Fluids With Superconducting Quantum Interference Device Transduction

This thesis describes experiments developing the use of Nanoelectromechanical systems as low temperature sensors, and for use as nanoscale probes in quantum fluids. The investigations revolve around the characterisation of these devices at low temperatures and their interaction with a DC Superconducting Quantum Interference Device (SQUID). The report begins with the background of NEMS research in the field of low temperature research and proceeds to discuss the important theoretical concepts around a doubly clamped beam resonator. The equivalent electrical circuit for a NEMS in the relevant transduction scheme is developed before a discussion of the experimental techniques used throughout the project. The first set of experiments involving vacuum measurements are described and the interaction between the NEMS and SQUID characterised with a qualitative model, demonstrating the ability to cool the first mode of the resonator with specific SQUID settings, and the ability to induce self-sustained oscillations. The process of designing and fabricating a new type of experimental cell for NEMS that is capable of better thermalisation is described, which enables further experiments in liquid helium. The important properties of helium with respect to immersed objects subject to excitations is discussed to enable examination of the preliminary results obtained from the new cell, before conclusions are drawn and further work discussed.