Development of superconducting thin film travelling wave parametric amplifiers

Ultra low-noise amplification is crucial for various fundamental physics platforms, including microwave/mm/sub-mm astronomy, dark matter search experiments, neutrino mass experiments, and qubit readout. Superconducting kinetic inductance travelling-wave parametric amplifiers (KITWPAs) are a recent development in amplifier technology, which are able to achieve high gain over broad bandwidth by efficiently transferring power from a strong ‘pump’ wave to a detected weak ‘signal’ wave via the wave mixing mechanisms in a non-linear medium comprising a high kinetic inductance wire. They have been experimentally verified to achieve high gain over broad bandwidth and quantum-limited noise performance with negligible heat dissipation, making them a natural successor to the current generation of semiconductor-based high electron mobility transistor (HEMT) amplifiers, which are the current standard in low-noise amplification. The elimination of the resonant architecture associated with earlier parametric amplifiers removes the narrow-band restrictions on these KITWPAs, which combined with their low heat dissipation and power requirements makes them readily scalable to arrays for large pixel count applications, such as the readout of astronomical detector arrays or qubit arrays.
This thesis focuses on the development of microwave KITWPAs in the frequency range of 2-18 GHz, made from titanium nitride (TiN) superconducting transmission lines, a material chosen as it displays many of the desired characteristics for KITWPA operation, namely high resistivity, high kinetic inductance, and mechanical robustness, as well as being a commonly used material in the field of microwave kinetic inductance detectors (MKIDs). The choice in material and topology for a KITWPA device, however, is not typically discussed in the literature, hence to understand the design considerations for a KITWPA device, we commence an investigation into KITWPA material and topology choice. Based on this analysis, we present an optimised TiN KITWPA design, which was designed using a commercial 3-D electromagnetic simulator (HFSS) and a complementary python package (SuperTWPA).
Although measurements of our KITWPA devices revealed unexpected losses, we were able to achieve a peak averaged gain of 5 dB with a bandwidth of ∼ 3 − 13 GHz when operating in a three-wave mixing (3WM) mode, making this, to the best of our knowledge, the first broadband gain measurement of a TiN KITWPA reported in the literature. The behaviour of the TiN film additionally points to physics beyond standard BCS theory, which could form the basis of future analysis of the microphysics of the material. We conclude our experimental work with a number of design improvements, which we believe could ultimately lead to a high-gain TiN KITWPA device.
At time of writing this thesis, KITWPAs are yet to be widely used in large-scale experiments due to a number of operational obstacles. We, therefore, conclude this thesis with a number of design concepts that could provide solutions to these operational obstacles, beginning with a dual-pump KITWPA to provide wideband amplification at millimetre (mm) frequencies, before introducing a balanced KITWPA concept; a novel parallel TWPA architecture, which we demonstrate to be able solve the signal-idler contamination problem in KITWPAs and to simplify the pump injection and cancellation schemes, paving the way for the widespread operation of KITWPAs in ultra-sensitive experimental setups.

Advisor: Tan, B
Leek, P