Large amplitude driving of a persistent current qubit

Abstract

In this thesis, the persistent current qubit in the presence of large amplitude microwave radiation is studied. Three main results are presented in this work. A new coherent quasi classical regime has been observed, where coherent quantum dynamics persist even while transitions between energy levels are caused by many photon modes simultaneously. A new theoretical treatment of this regime has been developed, and remarkable agreement between theory and experiment is observed. Also presented is a novel application of strong driving, where unwanted excited state population is cooled to the ground state by utilizing a second avoided crossing. This method of cooling, via a third, ancillary qubit level, is analogous to atomic sideband cooling. Cooling from 400mK to 3mK has been achieved. Finally, a new type of spectroscopy is presented, where an entire manifold of quantum levels is characterized with a single driving frequency, by studying the amplitude dependence of the qubit's behavior. Characterization of energy level spacings reaching 120GHz is achieved with radiation on the order of 0.1GHz.