dc SQUID Phase Qubit
| dc.contributor.advisor | Wellstood, Frederick C | en_US |
| dc.contributor.author | palomaki, tauno | en_US |
| dc.contributor.department | Physics | en_US |
| dc.contributor.publisher | Digital Repository at the University of Maryland | en_US |
| dc.contributor.publisher | University of Maryland (College Park, Md.) | en_US |
| dc.date.accessioned | 2008-10-11T05:51:52Z | |
| dc.date.available | 2008-10-11T05:51:52Z | |
| dc.date.issued | 2008-08-06 | en_US |
| dc.description.abstract | This thesis examines the behavior of dc SQUID phase qubits in terms of their proposed use in a quantum computer. In a phase qubit, the two lowest energy states (n=0 and n=1) of a current-biased Josephson junction form the qubit states, with the gauge invariant phase difference across the junction being relatively well defined. In a dc SQUID phase qubit, the Josephson junction is isolated from the environment using an inductive isolation network and Josephson junction, which are connected across the phase qubit junction to form a dc SQUID. Five dc SQUID phase qubits were examined at temperatures down to 25 mK. Three of the devices had qubit junctions that were Nb/AlOx/Nb junctions with critical currents of roughly 30 microamps. The other two had Al/AlOx/Al junctions with critical currents of roughly 1.3 microamps. The device that had the best performance was an Al/AlOx/Al device with a relaxation time of 30 ns and a coherence time of 24 ns. The devices were characterized using microwave spectroscopy, Rabi oscillations, relaxation and Ramsey fringe measurements. I was also able to see coupling between two Nb/AlOx/Nb dc SQUID phase qubits and perform Rabi oscillations with them. The Nb/AlOx/Nb devices had a relaxation time and coherence time that were half that of the Al/AlOx/Al device. One of the goals of this work was to understand the nature of parasitic quantum systems (TLSs) that interact with the qubit. Coupling between a TLS and a qubit causes an avoided level crossing in the transition spectrum of the qubit. In the Al/AlOx/Al devices unintentional avoided level crossings were visible with sizes up to 240 MHz, although most visible splittings were of order ~20 MHz. The measured spectra were compared to a model of the avoided level crossing based on the TLSs coupling to the junction, through either the critical current or the voltage across the junction. | en_US |
| dc.format.extent | 5640931 bytes | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | http://hdl.handle.net/1903/8575 | |
| dc.language.iso | en_US | |
| dc.subject.pqcontrolled | Physics, Condensed Matter | en_US |
| dc.subject.pquncontrolled | qubit | en_US |
| dc.subject.pquncontrolled | Josephson junction | en_US |
| dc.subject.pquncontrolled | quantum computation | en_US |
| dc.subject.pquncontrolled | superconductor | en_US |
| dc.subject.pquncontrolled | phase | en_US |
| dc.title | dc SQUID Phase Qubit | en_US |
| dc.type | Dissertation | en_US |
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