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Title: Studies of phenomena arising from the non-linearity of the Josephson junction
Author: Long, George
ISNI:       0000 0004 8500 6945
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2019
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Non-linear quantum devices employing superconducting resonators have drawn much attention since the realisation of quantum information processing. I outline the design, fabrication and behaviour of several devices in which niobium half-wavelength coplanar waveguide (CPW) superconducting resonators are modified with the inclusion of Josephson elements. The configuration of the Josephson elements (single junction and RF SQUIDs) and their position in the cavity are varied to explore and exploit both odd and even orders of the non-linear Josephson inductance. The Josephson elements were produced in two distinct ways. The primary focus was the development of shadow evaporated aluminium Josephson junctions deposited within an etched gap in the central conductor of a niobium CPW resonator. The samples were intended to be operated as amplitude bifurcation detectors for low power input signals however unexpected phenomena arose with the observation of well-defined, power-dependent modes appearing in the spectra. The nature and behaviours of these modes are explored and characterised. A secondary objective was the development of samples based on weak-link constrictions (nanobridges) patterned into the niobium resonators central conductor via electron beam lithography and reactive ion etching. These devices focus around a RF SQUID geometry, modifying the current-phase relation of the constriction to take advantage of an even order non-linearity and three-wave mixing. The phenomena arising in these circuits are explored.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Josephson effect ; Superconducting circuits ; Josephson junction ; Nanobridge ; Superconducting resonators