Superconducting flux transformers for the modulation of flux-tunable resonators

Abstract

Pushing the limits of quantum mechanics to larger objects is a goal of current research efforts. One approach to test the limits of quantum mechanics is to achieve quantum superposition with a macroscopic object on the order of micrometers. A possible experimental approach in this direction is given by coupling a magnetically levitated particle to a superconducting flux-tunable resonator. This system can allow us to sense the particle’s motion and the flux-tunable resonator will act as the quantum sensor and the readout for the particle. This system exploits flux coupling between the particle and the flux-tunable resonator. An approach of realizing this flux coupling is by implementing a flux transformer which is the main goal of this thesis. In this thesis we demonstrate a theoretical model to optimize the geometry of the flux transformer for maximum flux transfer efficiency. The theoretical analysis is verified with simulations on COMSOL Multiphysics. Then, a reliable fabrication recipe has been developed which had high yield of superconducting flux transformer and flip-chip devices. A novel flip-chip assembly technique was implemented with usage of Indium microspheres as superconducting interconnects. The thin-film of the materials used for the flux transformer and the flip-chip devices were characterized to demonstrate their superconductivity. Finally, a proof-of-principle for flip-chip based modulation of a flux-tunable resonator is demonstrated.