Energy Down-Conversion Between Classical Electromagnetic Modes via a Quantum Mechanical RF-SQUID

This thesis examines the interaction between an RF SQUID ring coupled to two high Q resonant circuit measurement systems, operating at 24 MHz and 1 GHz at 4.2K. Energy is coupled to the system via a microwave source and is used to modulate the screening current of the ring and also to excite transitions between the underlying eigenenergy bands of the ring via non-adiabatic interaction. We study the current literature on such systems, used as qubits and as the building blocks for quantum computing and information processing elements. We discuss the relevance ofour system to those reviewed and suggest useful future direction for this work. We show that the point contact RF-SQUID coupled to multiple resonant circuits can be used as a model for studying the interaction between flux qubits and electromagnetic modes and provides insight in designing future practical qubit systems. In this work a new method of data acquisition is introduced, providing a much improved visualisation of the phase space. A 1 GHz measurement system is used to provide evidence of energy down-conversion from the input electromagnetic mode for a range of frequencies, via the SQUID ring. Previous work has focused on high ratio down conversion of up to 18,806: 1. Our data now shows a ratio of 1.67:1 and allows our fully quantum· mechanical theoretical model to be more usefully applied to give further insight about the system. As well as the 1 GHz measurement system, we also consider measurements from 24 MHz readout for a range of point contact weak links. We conclude the experimental results by showing down conversion taking place to both tank circuits simultaneously from the input mode, operating at 3.9 GHz. Finally we present simulations using the fully quantum model ofthe system, discuss the limitations and draw useful conclusions about the quantum nature of the down-conversion mechanism.EThOS - Electronic Theses Online ServiceGBUnited Kingdo