SPECTROSCOPY OF TWO LEVEL DEFECTS & QUASIPARTICLES IN SUPERCONDUCTING RESONATORS

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dc.contributor.advisorOsborn, Kevin Den_US
dc.contributor.advisorAnlage, Stevenen_US
dc.contributor.authorKohler, Timothyen_US
dc.contributor.departmentElectrical Engineeringen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2021-07-14T05:32:41Z
dc.date.available2021-07-14T05:32:41Z
dc.date.issued2021en_US
dc.description.abstractSuperconducting films are inherently limited by losses due to two-level system (TLS) defects within the amorphous oxide layers surrounding them and from quasiparticles in the film. In this thesis I will discuss novel theoretical and experimental methods toward understanding superconducting resonator loss from deleterious surface TLS defects as well as a loss transition from non-equilibrium quasiparticles in granular TiN. I will show using finite element solver software that a resonator with submicron linewidth and linespacing can be used to better characterize and simulate surface TLS as part of a circuit QED system. I have observed individual surface TLS and found coupling values in the range of g/2π =50 kHz -280 kHz with a maximum dipole moment pz-max = 4.5 Debye (.93 eÅ). I have found in in simulation of experiment that over 80% of the strongly coupled TLS reside within 50 nm of the corner between the Metal-Substrate (MS) and Substrate-Air (SA) interface. Additionally I have studied a loss transition from non-equilibrium quasiparticles in TiN films. These films exhibit an anomalous loss dependence on substrate treatment and film thickness. The films of interest are ones grown thin on oxidized substrates, which exhibit an order of magnitude decrease in internal quality factor (Qi) relative to either thicker ˝films or films grown without the oxidized substrate. These films additionally exhibit a grain size on average of 7.5 nm, a higher inhomogeneous gap, a transition to lower stress and a preference for the [111] crystal growth. The temperature dependence of the conductivity is fit and a factor of two difference in quasiparticle lifetime is found between the two films where the thinner film has a shorter lifetime. A two gap quasiparticle trapping model is fit to the temperature dependent loss data. The data is consistent with a model where non-equilibrium quasi-particles are trapped in low gapped grains on the inside of the films. From these works and others presented in my thesis the understanding of TLSs on surfaces and non-equilibrium quasiparticles in TiN has improved. This will help illuminate some of the most important absorption mechanisms plaguing superconducting qubits and resonators.en_US
dc.identifierhttps://doi.org/10.13016/trei-78bx
dc.identifier.urihttp://hdl.handle.net/1903/27436
dc.language.isoenen_US
dc.subject.pqcontrolledCondensed matter physicsen_US
dc.subject.pqcontrolledQuantum physicsen_US
dc.subject.pquncontrolledlossen_US
dc.subject.pquncontrolledResonatoren_US
dc.subject.pquncontrolledSpectroscopyen_US
dc.subject.pquncontrolledSuperconductingen_US
dc.subject.pquncontrolledTiNen_US
dc.subject.pquncontrolledTLSen_US
dc.titleSPECTROSCOPY OF TWO LEVEL DEFECTS & QUASIPARTICLES IN SUPERCONDUCTING RESONATORSen_US
dc.typeDissertationen_US

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