DEPARTMENT OF PHYSICS DISSERTATION DEFENSE: Elizabeth (Cady) van Assendelft

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Title:  Josephson-junction based frequency upconverters for DC-VHF electromagnetic sensing

Abstract:  Precision electromagnetic measurements below 300MHz have broad scientific applications, including sub-μeV axion searches using superconducting lumped-element resonators or polarized nuclear spin samples. To meet the high sensitivity and broad bandwidth required by these applications, I present a device architecture that implements cavity optomechanics-style measurement in a flux-to-voltage amplifier. The Radiofrequency Quantum Upconverter (RQU) consists of a three-branch Josephson-junction interferometer terminating a microwave resonator. The nonlinearity of the Josephson junctions implements a parametric interaction, where an incoming inductively coupled flux signal is upconverted to the microwave regime. In addition to standard phase-preserving measurement that can theoretically reach the Standard Quantum Limit (SQL), the RQU can also be used to implement quantum metrology techniques such as backaction-evasion. I present details of this device architecture and demonstrate results from first-generation RQU devices.