Coupled superconducting microwave resonators for studies of electro-mechanical interaction

Gunupudi, Bindu (2015). Coupled superconducting microwave resonators for studies of electro-mechanical interaction. University of Birmingham. Ph.D.

Preview

Gunupudi15PhD.pdf
PDF - Accepted Version
Download (16MB)

Abstract

The motivation behind the work described in this thesis is to study the coupling between a nanobar and a pair of identical, coupled, superconducting microwave resonators, where the splitting frequency at their avoided crossing is close to the nanobar resonant frequency.

The splitting frequency as a function of the coupling between the microwave resonators has been thoroughly investigated by theoretical simulations in COMSOL and AIM Spice, and experimentally verified by low temperature measurements. Deviations of the measured splitting from the theoretical values and reflection measurements showed that the resonators required to be tuned in order to reach the avoided crossing.

A novel tuning mechanism was devised and implemented in-situ in the experiments. Tuning of resonators was successfully achieved and there was excellent agreement of the measured splitting with the predicted values. A wide frequency tuning range of 50 MHz was obtained, more than required for our experiments, without degrading the high resonator quality factors (~10\(^5\)). This enabled the measurement of the inherent splitting of the coupled resonator frequencies at the avoided crossing, and more importantly, paves the way for studies of electro-mechanical interaction.

In the absence of nanobars, an analogous experiment that varied the resonator inductance instead of
its capacitance was devised. The resonant frequency of one of the resonators was perturbed using a small
amplitude magnetic field using a coil placed underneath the sample, a case that has not been previously
explored. The results obtained from these preliminary experiments have shown a good agreement with the
theoretical predictions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):