Parametric Amplification, Shockwave Formation and Quasiparticle Generation in Superconducting Metamaterials

Ó Peatáin, Searbhán and Pashkin, Yuri (2025) Parametric Amplification, Shockwave Formation and Quasiparticle Generation in Superconducting Metamaterials. PhD thesis, Lancaster University.

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Abstract

Superconducting parametric amplifiers are an already widespread technology, but as the requirements of measurement become more and more stringent in new experiments an evolution of the technology is required. This thesis covers the theory, characterisation and design of superconducting travelling wave parametric amplifiers (TWPAs). The basic theory for this type of device is not new, as amplification in travelling wave structures can be achieved simply by embedding a non-linear reactance into a transmission line. For our purposes, we achieve this by utilising either the Josephson inductance of an rf-SQUID or the kinetic inductance of thin superconducting films. This thesis covers in detail the theory of operation of these devices to achieve three wave mixing amplification at the quantum limit. We begin by discussing the basic theory of lumped element transmission lines and the nonlinearities of the superconducting elements. Simulation techniques are then introduced, validated and applied to the study of these devices and the detrimental effects of impedance mismatches, fabrication tolerances, parasitic reactances and losses on the TWPA performance. Two realised TWPA devices based on the nonlinearity of the rf-SQUID are investigated using transmission measurements, with the results compared to theory to improve our understanding. The effects and origins of losses in the devices are investigated thoroughly as this has been identified as key to the understanding and improvement of future devices. We finish this thesis with a set of proposals for TWPA devices that should overcome the problems discovered in previous proposals and realised devices that are discussed in this thesis. The results of this thesis should allow for the final steps towards achieving three wave mixing in a Josephson travelling wave parametric amplifier to be taken, with key considerations in terms of fabrication and design of a new generation of devices discussed throughout.